Filed pursuant to Rule 497
Registration Statement No. 333-225447

PROSPECTUS SUPPLEMENT

(To Prospectus Dated July 13, 2018)

Up to $35,000,000

Common Stock

We are an externally managed, closed-end, non-diversified management investment company that has elected to be treated as a business development company (“BDC”) under the Investment Company Act of 1940, as amended (the “1940 Act”). For federal income tax purposes, we have elected to be treated as a regulated investment company (“RIC”) under Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”). Generally, our investment objectives are to: (i) achieve and grow current income by investing in debt securities of established businesses that we believe will provide stable earnings and cash flow to pay expenses, make principal and interest payments on our outstanding indebtedness and make distributions to stockholders that grow over time; and (ii) provide our stockholders with long-term capital appreciation in the value of our assets by investing in equity securities, generally in combination with the aforementioned debt securities, of established businesses that we believe can grow over time to permit us to sell our equity investments for capital gains.

We previously entered into separate sales agreements, each dated February 22, 2018, each a “Sales Agreement” and collectively the “Sales Agreements,” with Cantor Fitzgerald & Co., Ladenburg Thalmann & Co. Inc. and Wedbush Securities Inc. (each a “Sales Agent” and collectively the “Sales Agents”), relating to the shares of our common stock, par value $0.001 per share, offered pursuant to this prospectus supplement and the accompanying prospectus. The Sales Agreements provide that we may offer and sell up to an aggregate offering price of $35,000,000 of our common stock from time to time through the Sales Agents. As of the date of this prospectus supplement, we have sold 296,236 shares of our common stock under the Sales Agreements and have the ability to sell an aggregate offering price of up to $31.8 million of our common stock under the Sales Agreements. Subject to the terms of the Sales Agreements, the Sales Agents are not required to sell any specific number or dollar amounts of securities but will act as our sales agents using commercially reasonable efforts consistent with their normal trading and sales practices, on mutually agreed terms between the Sales Agents and us.

The Sales Agents will be entitled to compensation under the terms of the Sales Agreements at a commission of up to 2.0% of the gross sales price per share of common stock sold pursuant to the Sales Agreements. In connection with the sale of our common stock on our behalf, the Sales Agents will be deemed to be “underwriters” within the meaning of the Securities Act of 1933, as amended (the “Securities Act”), and the compensation of the Sales Agents will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification and contribution to the Sales Agents against certain civil liabilities, including liabilities under the Securities Act.

Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be made by transactions that are deemed to be part of an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act, by means of ordinary brokers’ transactions that qualify for delivery of a prospectus to the Nasdaq Global Select Market (“Nasdaq”), in accordance with Rule 153 under the Securities Act, or such other sales as may be agreed by us and the Sales Agents, at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices. The offering of shares of common stock pursuant to the Sales Agreements will terminate upon the earlier of (1) the sale of shares of common stock having an aggregate offering price of $35,000,000, (2) the termination of the Sales Agreements by us or the Sales Agents, or (3) the date six years from the date of the Sales Agreements. See “Plan of Distribution” beginning on page S-44 of this prospectus supplement.

Our common stock is traded on Nasdaq under the symbol “GAIN.” On August 28, 2018 the last reported sale price of our common stock on Nasdaq was $12.00 per share. The net asset value (“NAV”), per share of our common stock on June 30, 2018 (the last date prior to the date of this prospectus supplement as of which we determined NAV) was $11.57. You are urged to obtain current market quotations of our common stock.

Shares of closed-end investment companies, including BDCs, frequently trade at a discount to their NAV. If our shares trade at a discount to our NAV, it will likely increase the risk of loss for purchasers in this offering. On August 9, 2018, our stockholders voted to allow us to issue common stock at a price below NAV per share for the period ending on the one year anniversary of the date of our 2018 Annual Meeting of Stockholders. Our stockholders did not specify a maximum discount below NAV at which we are able to issue our common stock, although the number of shares sold in each offering may not exceed 25% of our outstanding common stock immediately prior to such sale. In addition, we cannot issue shares of our common stock below NAV unless our board of directors (“Board of Directors”) determines that it would be in our and our stockholders’ best interests to do so. Sales of common stock at prices below NAV per share dilute the interests of existing stockholders, have the effect of reducing our NAV per share and may reduce our market price per share. In addition, continuous sales of common stock below NAV may have a negative impact on total returns and could have a negative impact on the market price of our shares of common stock. See “Sales of Common Stock Below Net Asset Value” in this prospectus supplement and in the accompanying prospectus.

The securities in which we invest generally would be rated below investment grade if they were rated by rating agencies. Below investment grade securities, which are often referred to as “junk,” have predominantly speculative characteristics with respect to the issuer’s capacity to pay interest and repay principal. They may also be difficult to value and are illiquid.

Investing in shares of our common stock involves a high degree of risk. Before investing, you should read the material risks described in the “Risk Factors” section beginning on page S-13 of this prospectus supplement and beginning on page 13 of the accompanying prospectus.

This prospectus supplement and the accompanying prospectus contain important information you should know before investing in our common stock, including information about risks. Please read it before you invest and retain it for future reference. Additional information about us, including our annual, quarterly and current reports, has been filed with the Securities and Exchange Commission (the “SEC”), and can be accessed at its website at www.sec.gov. This information is also available free of charge by calling us collect at (703) 287-5893 or on the investor relations section of our corporate website located at www.gladstoneinvestment.com. You may also call us collect at this number to request other information or to make a shareholder inquiry. See “Where You Can Find More Information” on page S-46 of this prospectus supplement. The SEC has not approved or disapproved these securities or passed upon the adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is August 29, 2018 

ABOUT THIS PROSPECTUS SUPPLEMENT

This document is presented in two parts. The first part is comprised of this prospectus supplement, which describes the specific terms of this common stock at-the-market offering and certain other matters relating to us. The second part, the accompanying prospectus, contains a description of our common stock and provides more general information, some of which does not apply to this offering, regarding securities that we may offer from time to time. To the extent that the information contained in this prospectus supplement differs or varies from the information contained in the accompanying prospectus, the information in this prospectus supplement will supersede such information.

This prospectus supplement is part of a registration statement on Form N-2 (Registration No. 333-225447) that we have filed with the SEC relating to the securities offered hereby. This prospectus supplement does not contain all of the information that we have included in the registration statement and the accompanying exhibits and schedules thereto in accordance with the rules and regulations of the SEC, and we refer you to such omitted information. It is important for you to read and consider all of the information contained in this prospectus supplement and the accompanying prospectus before making your investment decision. You should also read and consider the additional information incorporated by reference into this prospectus supplement and the accompanying prospectus. See “Where You Can Find More Information” in this prospectus supplement.

The distribution of this prospectus supplement and the accompanying prospectus and this offering of the securities may be restricted by law in certain jurisdictions. This prospectus supplement and the accompanying prospectus are not an offer to sell or a solicitation of an offer to buy shares of our common stock in any jurisdiction where such offer or any sale would be unlawful. Persons who come into possession of this prospectus supplement and the accompanying prospectus should inform themselves of and observe any such restrictions.

You should rely only on the information contained in this prospectus supplement and the accompanying prospectus in making an investment decision. We have not, and the Sales Agents have not, authorized any other person to provide you with information that is different or additional. If anyone provides you with different or additional information, you should not rely on it. We do not, and the Sales Agents and their affiliates do not, take any responsibility for, and can provide no assurances as to, the reliability of any information that others may provide to you. You should not assume that the information in this prospectus supplement or the accompanying prospectus is accurate as of any date other than their respective dates, regardless of the time of delivery of this prospectus supplement, the accompanying prospectus or any sales of our common stock. Our business, financial condition, liquidity, results of operations, funds from operations and prospects may have changed since those dates. To the extent required by law, we will amend or supplement the information contained in this prospectus supplement and the accompanying prospectus.

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TABLE OF CONTENTS

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FEES AND EXPENSES

The following table is intended to assist you in understanding the costs and expenses that an investor in this offering will bear directly or indirectly. We caution you that some of the percentages indicated in the table below are estimates and may vary. Except where the context suggests otherwise, whenever this prospectus supplement contains a reference to fees or expenses paid by “us” or “Gladstone Investment,” or that “we” will pay fees or expenses, stockholders will indirectly bear such fees or expenses as investors in Gladstone Investment. The following annualized percentages were calculated based on actual expenses incurred in the quarter ended June 30, 2018 and average net assets for the quarter ended June 30, 2018 and do not include events occurring subsequent thereto. The table and examples below include all fees and expenses of our consolidated subsidiaries.

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Pursuant to the requirements of the 1940 Act, the Adviser makes available significant managerial assistance to our portfolio companies. The Adviser may also provide other services to our portfolio companies under certain agreements and may receive fees for services other than managerial assistance. Such services may include, but are not limited to: (i) assistance obtaining, sourcing or structuring credit facilities, long term loans or additional equity from unaffiliated third parties; (ii) negotiating important contractual financial relationships; (iii) consulting services regarding restructuring of the portfolio company and financial modeling as it relates to raising additional debt and equity capital from unaffiliated third parties; and (iv) primary role in interviewing, vetting and negotiating employment contracts with candidates in connection with adding and retaining key portfolio company management team members. The Adviser non-contractually, unconditionally, and irrevocably credits 100% of these fees against the base management fee that we would otherwise be required to pay to the Adviser; however, pursuant to the terms of the Advisory Agreement, a small percentage of certain of such fees, is retained by the Adviser in the form of reimbursement, at cost, for tasks completed by personnel of the Adviser and primarily for the valuation of portfolio companies. For the quarter ended June 30, 2018, $1.0 million of these fees were non-contractually, unconditionally and irrevocably credited against the base management fee. See “Business —Transactions with Related Parties—Investment Advisory and Management Agreement” and “Management—Certain Transactions—Investment Advisor and Administrator” in the accompanying prospectus.

The capital gains-based incentive fee equals 20% of our net realized capital gains in excess of unrealized depreciation since our inception, if any, computed as all realized capital gains net of all realized capital losses and unrealized capital depreciation since our inception, less any prior payments, and is payable at the end of each fiscal year. During the three months ended June 30, 2018, we recorded a capital gains-based incentive fee of $6.5 million in accordance with the provisions of U.S. generally accepted accounting principles (“GAAP”), which is not contractually due under the terms of the Advisory Agreement. All capital gains-based incentive fees which are not contractually due under the terms of the Advisory Agreement were excluded for purposes of calculating the incentive fees included in the Fees and Expenses table above.

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No credits were applied to the incentive fee for the three months ended June 30, 2018; however, the Adviser may credit such fee in the future.

Examples of how the incentive fee would be calculated are as follows:

= 100.0% × (2.00% - 1.75%)

= 0.25%

= (100.0% × (“catch-up”: 2.1875% - 1.75%)) + (20.0% × (2.30% - 2.1875%))

= (100.0% × 0.4375%) + (20.0% × 0.1125%)

= 0.4375% + 0.0225%

= 0.46%

= 20.0% × (6.0% - 1.0%)

= 20.0% × 5.0%

= 1.0%

For a more detailed discussion of the calculation of the two-part incentive fee, including the capital gains-based incentive fee calculation under GAAP, see “Business—Transactions with Related Parties—Investment Advisory and Management Agreement” in the accompanying prospectus.

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Example

The following example demonstrates the projected dollar amount of total cumulative expenses that would be incurred over various periods with respect to a hypothetical investment in our common stock. In calculating the following expense amounts, we have assumed that our annual operating expenses would remain at the levels set forth in the table above. The example below and the expenses in the table above should not be considered a representation of our future expenses, and actual expenses may be greater or less than those shown. While the example assumes, as required by the SEC, a 5.00% annual return, our performance will vary and may result in a return greater or less than 5.00%.

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RISK FACTORS

You should carefully consider the risks described below and all other information contained in this prospectus supplement and the accompanying prospectus before making a decision to purchase our shares. The risks and uncertainties described below are not the only ones facing us. Additional risks and uncertainties not presently known to us, or not presently deemed material by us, may also impair our operations and performance.

If any of the following risks actually occur, our business, financial condition or results of operations could be materially adversely affected. If that happens, the trading price of our securities and NAV of our common stock could decline, and you may lose all or part of your investment.

Our management will have broad discretion in the use of the net proceeds from this offering and may allocate the net proceeds from this offering in ways that you and other stockholders may not approve of.

Our management will have broad discretion in the use of the net proceeds, including for any of the purposes described in the section entitled “Use of Proceeds,” and you will not have the opportunity as part of your investment decision to assess whether the net proceeds are being used in ways with which you may not agree or may not otherwise be considered appropriate. Because of the number and variability of factors that will determine our use of the net proceeds from this offering, their ultimate use may vary substantially from their currently intended use. The failure of our management to use these funds effectively could harm our business. Pending their use, we may invest the net proceeds from this offering in short-term, investment grade, interest-bearing securities. These investments may not yield a favorable return to our stockholders.

We may be unable to invest a significant portion of the net proceeds of this offering on acceptable terms.

Delays in investing the net proceeds raised in an offering or from exiting an investment, prepayment of an investment or other capital source may cause our performance to be worse than that of other fully invested BDCs or other lenders or investors pursuing comparable investment strategies. We cannot assure you that we will be able to identify any investments that meet our investment objective or that any investment that we make will produce a positive return. We may be unable to invest the net proceeds from any offering, from exiting an investment, prepayment of an investment or other capital source on acceptable terms within the time period that we anticipate or at all, which could harm our financial condition and operating results.

Market interest rates may have an effect on the value of our common stock.

One of the factors that will influence the price of our common stock will be the distribution yield on our common stock (as a percentage of the price of our common stock) relative to market interest rates. An increase in market interest rates, which, while currently at low levels relative to historical rates, although they have recently experienced gradual increases, may lead prospective purchasers of our common stock to expect a higher distribution yield and higher interest rates would likely increase our borrowing costs and potentially decrease funds available for distribution. Thus, higher market interest rates could cause the market price of our common stock to decrease.

Our most recent NAV was calculated on June 30, 2018 and our NAV when calculated as of September 30, 2018 and subsequent periods may be higher or lower.

As of June 30, 2018, our NAV per share was $11.57, which was based on the fair value our investments that were reviewed and approved by our Board of Directors (and the valuation committee thereof). NAV per share as of September 30, 2018, and following quarters, may be higher or lower than $11.57 based on potential changes in valuations, issuances of securities, or distributions paid and earnings for the quarter then ended. Our Board of Directors determines the fair value of our portfolio investments on a quarterly basis, and if our September 30, 2018 fair value is less than the June 30, 2018 fair value, we will record an unrealized loss on our investment

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portfolio. If the fair value is greater, we will record an unrealized gain on our investment portfolio. Upon publication of our next quarterly NAV per share determination (generally in our next Quarterly Report on Form 10-Q), the market price of our common stock may fluctuate materially.

Shares of closed-end investment companies, including BDCs, frequently trade at a discount to their NAV per share, which may restrict our ability to grow and adversely impact our ability to increase or maintain our distributions.

Shares of closed-end investment companies, including BDCs, frequently trade at a discount from NAV per share. This characteristic of shares of closed-end investment companies is separate and distinct from the risk that our NAV per share will decline. As with any stock, the price of our shares will fluctuate with market conditions and other factors. If shares are sold, the price received may be more or less than the original investment. Whether investors will realize gains or losses upon the sale of our shares will not depend directly upon our NAV, but will depend upon the market price of the shares at the time of sale. Since the market price of our shares will be affected by such factors as the relative demand for and supply of the shares in the market, general market and economic conditions and other factors beyond our control, we cannot predict whether the shares will trade at, below or above our NAV per share.

Under the 1940 Act, we are generally not able to issue additional shares of our common stock at a price below NAV per share to purchasers other than our existing common stockholders through a rights offering without first obtaining the approval of our stockholders, our directors who have no financial interest in the transaction, and our independent directors. Additionally, at times when our common stock is trading below its NAV per share, our dividend yield may exceed the weighted average returns that we would expect to realize on new investments that would be made with the proceeds from the sale of such stock, making it unlikely that we would determine to issue additional common shares in such circumstances. Thus, for as long as our common stock may trade below NAV per share we will be subject to significant constraints on our ability to raise capital through the issuance of common stock. Additionally, an extended period of time in which we are unable to raise capital may restrict our ability to grow and adversely impact our ability to increase or maintain our distributions.

If we sell shares of our common stock at a discount to our NAV per share, stockholders who do not participate in such sale will experience immediate dilution in an amount that may be material.

At our 2018 Annual Meeting of Stockholders our stockholders approved our ability, subject to the condition that the maximum number of shares salable below NAV pursuant to this authority in any particular offering that could result in such dilution is limited to 25% of our then outstanding common stock immediately prior to each such offering, to sell shares of our common stock at any level of discount from NAV per share for a period of 12 months. It should be noted that, theoretically, we may offer up to 25% of our then outstanding common stock each day. The issuance or sale by us of shares of our common stock at a discount to NAV poses a risk of dilution to our stockholders. In particular, stockholders who do not purchase additional shares of common stock at or below the discounted price in proportion to their current ownership will experience an immediate decrease in NAV per share (as well as in the aggregate NAV of their shares of common stock if they do not participate at all). These stockholders will also experience a disproportionately greater decrease in their participation in our earnings and assets and their voting power than the increase we experience in our assets, potential earning power and voting interests from such issuance or sale. In addition, such sales may adversely affect the price at which our common stock trades. For additional information about possible sales below NAV per share, see “Sales of Common Stock Below Net Asset Value” in this prospectus supplement and in the accompanying prospectus.

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We may not be permitted to declare a dividend or make any distribution to stockholders or repurchase shares until such time as we satisfy the asset coverage tests under the provisions of the 1940 Act that apply to BDCs. As a BDC, we have the ability to issue senior securities only in amounts such that our asset coverage, as defined in the 1940 Act, equals at least 200% (currently) (or 150%, effective April 10, 2019, unless earlier approved by our stockholders) after each issuance of senior securities. If the value of our assets declines, we may be unable to satisfy this test. If that happens, we may be required to sell a portion of our investments and, depending on the nature of our leverage, repay a portion of our debt at a time when such sales and/or repayments may be disadvantageous.

Regulations governing our operation as a BDC and RIC will affect our ability to raise, and the way in which we raise, additional capital or borrow for investment purposes, which may have a negative effect on our growth. As a result of the annual distribution requirement to qualify as a RIC, we may need to periodically access the capital markets to raise cash to fund new investments. We may issue senior securities representing indebtedness, including borrowing money from banks or other financial institutions, or senior securities that are stock, such as our outstanding Term Preferred Stock, only in amounts such that our asset coverage, as defined in the 1940 Act, equals at least 200% (currently) or 150% (effective April 10, 2019, unless earlier approved by the Company’s stockholders) after each such incurrence or issuance. See “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Overview—Recent Developments—Small Business Credit Availability Act.” Further, we may not be permitted to declare a dividend or make any distribution to our outstanding stockholders or repurchase shares until such time as we satisfy this test. Our ability to issue different types of securities is also limited. Compliance with these requirements may unfavorably limit our investment opportunities and reduce our ability in comparison to other companies to profit from favorable spreads between the rates at which we can borrow and the rates at which we can lend. As a BDC, therefore, we intend to continuously issue equity at a rate more frequent than our privately owned competitors, which may lead to greater stockholder dilution. We have incurred leverage to generate capital to make additional investments. If the value of our assets declines, we may be unable to satisfy the asset coverage test under the 1940 Act, which could prohibit us from paying distributions and could prevent us from qualifying as a RIC. If we cannot satisfy the asset coverage test, we may be required to sell a portion of our investments and, depending on the nature of our debt financing, repay a portion of our indebtedness at a time when such sales and repayments may be disadvantageous.

Recently-enacted legislation allows us to incur additional leverage under the 1940 Act, distinct from certain of our obligations under our Credit Facility and our Term Preferred Stock.

Historically, as a BDC, under the 1940 Act, we are generally required to maintain asset coverage of 200% for senior securities representing indebtedness (i.e., debt) or stock (i.e., preferred stock). On March 23, 2018, President Trump signed into legislation the Consolidated Appropriations Act of 2018, also known as the “omnibus spending package.” Included in Title VIII therein is the Small Business Credit Availability Act that includes certain regulations under the federal securities laws impacting BDCs. Among other items, the Small Business Credit Availability Act allows a BDC to increase the amount of debt it may incur or senior securities that are stock it may issue by modifying the asset coverage percentage from 200% to 150% (subject to specific approval and disclosure requirements).

On April 10, 2018, our Board of Directors, including a “required majority” (as such term is defined in Section 57(o) of the 1940 Act) thereof, approved the modified asset coverage requirements set forth in Section 61(a)(2) of the 1940 Act, as amended by the Small Business Credit Availability Act. As a result, the Company’s asset coverage requirements for senior securities will be changed from 200% to 150%, effective one year after the date of the Board of Director’s approval, on April 10, 2019, unless earlier approved by the Company’s stockholders. Under the current 200% asset coverage standard, we may borrow debt or issue senior securities in the amount of $1.00 for every $1.00 of equity in the Company. Starting from April 10, 2019, unless earlier approved by the Company’s stockholders, under the 150% asset coverage standard, we may borrow debt or issue senior securities in the amount of $2.00 for every $1.00 of equity in the Company. This reduction in the

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asset coverage ratio will allow us to double the amount of debt that we may incur and, therefore, your risk of an investment in us may increase. In addition, our base management fee is based on our average gross assets, which include investments made with proceeds of borrowings, and, as a result, if we were to incur additional leverage, base management fees paid to the Adviser would increase.

Notwithstanding the modified asset coverage leverage ratio under the 1940 Act described above, we currently remain subject to a minimum asset coverage requirement of 200% with respect to certain provisions of our Credit Facility and our outstanding Term Preferred Stock. If we drop below the 200% minimum asset coverage requirement, we may under certain circumstances be required to repay all outstanding indebtedness under our Credit Facility and redeem our then-outstanding Term Preferred Stock. In addition, in the event we fall below the 200% minimum asset coverage requirement, we may need to renegotiate our Credit Facility and issue additional series of term preferred stock with a lower asset coverage requirement. Such events, if they were to occur, could have a significant adverse effect on our business, financial condition, results of operations and cash flows.

If we fail to pay dividends on our Term Preferred Stock for two years, the holders of our Term Preferred Stock will be entitled to elect a majority of our directors.

The terms of our series of Term Preferred Stock provide for annual dividends of $1.6875, $1.6250, $1.5625 and $1.5938 per outstanding share of our Series B Term Preferred Stock, Series C Term Preferred Stock, Series D Term Preferred Stock and Series E Term Preferred Stock, respectively. In accordance with the terms of both of our series of Term Preferred Stock, if dividends thereon are unpaid in an amount equal to at least two years of dividends, the holders of such series of stock will be entitled to elect a majority of our Board of Directors.

Holders of our preferred stock and future holders of any securities ranking senior to our common stock have dividend, distribution and liquidation rights that are senior to the rights of the holders of our common stock.

The shares of our series of Term Preferred Stock have dividend, distribution and liquidation rights that are senior to the rights of the holders of our common stock. Further, in the future, we may attempt to increase our capital resources by making additional offerings of preferred equity securities or issuing debt securities. Upon liquidation, holders of our Term Preferred Stock, holders of our debt securities, if any, and lenders with respect to other borrowings, including the Credit Facility, would receive a distribution of our available assets in full prior to the holders of our common stock. Because our decision to issue securities in any future offering will depend on market conditions and other factors beyond our control, we cannot predict or estimate the amount, timing or nature of our future offerings. Thus, our common stockholders bear the risk of our future offerings reducing the per share trading price of our common stock and diluting their interest in us.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

All statements contained in this prospectus supplement or the accompanying prospectus, other than historical facts, may constitute “forward-looking statements.” These statements may relate to, among other things, future events or our future operating results, our business prospects and the prospects of our portfolio companies, actual and potential conflicts of interest with the Adviser and its affiliates, the use of borrowed money to finance our investments, the adequacy of our financing sources and working capital, and our ability to co-invest, among other factors. In some cases, you can identify forward-looking statements by terminology such as “estimate,” “may,” “might,” “believe,” “will,” “provided,” “anticipate,” “future,” “could,” “growth,” “plan,” “project,” “intend,” “expect,” “should,” “would,” “if,” “seek,” “possible,” “potential,” “likely” or the negative or other variations of such terms or comparable terminology. These forward-looking statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from any future results, levels of activity, performance or achievements expressed or implied by such forward-looking statements. Such factors include but are not limited to:

We caution readers not to place undue reliance on any such forward-looking statements, which speak only as of the date made. Actual results could differ materially from those anticipated in our forward-looking statements and future results could differ materially from historical performance. We have based forward-looking statements on information available to us on the date of this prospectus supplement. We undertake no obligation to publicly update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, after the date of this prospectus supplement or the accompanying prospectus, except as otherwise required by applicable law. The forward-looking statements contained in this prospectus supplement and the accompanying prospectus are excluded from the safe harbor protection provided by the Private Securities Litigation Reform Act of 1995 and Section 27A of the Securities Act.

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USE OF PROCEEDS

Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be by transactions that are deemed to be part of an “at the market offering” as defined in Rule 415(a)(4) under the Securities Act, by means of ordinary brokers’ transactions that qualify for delivery of a prospectus to Nasdaq in accordance with Rule 153 under the Securities Act or such other sales as may be agreed by us and the Sales Agents, at market prices prevailing at the time of sale, at prices related to prevailing market prices or at other negotiated prices. There is no guarantee that there will be any sales of our common stock pursuant to this prospectus supplement and the accompanying prospectus. Actual sales, if any, of our common stock under this prospectus supplement and the accompanying prospectus may be less than as set forth in this paragraph depending on, among other things, the market price of our common stock at the time of any such sale. As a result, the actual net proceeds we receive may be more or less than the amount of net proceeds estimated in this prospectus supplement. However, assuming the sale of all of the $35.0 million of common stock offered under this prospectus supplement and the accompanying prospectus, we anticipate that our net proceeds from this offering will be approximately $34.1 million, after deducting the maximum estimated sales commission payable to the Sales Agents and our estimated offering expenses of $0.2 million. As of the date of this prospectus supplement, we have sold 296,236 shares of common stock and have $31.8 million remaining availability under the Sales Agreements.

We intend to use the net proceeds from this offering first to pay down outstanding debt (which may include borrowings under the Credit Facility), if any, then to make investments in accordance with our investment objectives and strategy, with any remaining proceeds to be used for other general corporate purposes. As of the date of this prospectus supplement, we had $116.0 million outstanding under the Credit Facility, as amended in August 2018, and advances under the Credit Facility generally bear interest at 30-day LIBOR plus 2.85% per annum until August 22, 2021, with the margin then increasing to 3.10% for the period from August 23, 2021 to August 22, 2022, and increasing further to 3.35% thereafter through maturity. If not renewed or extended by August 22, 2021, all principal and interest will be due and payable on or before August 22, 2023. We intend to re-borrow under our Credit Facility to make investments in portfolio companies in accordance with our investment objectives depending on the availability of appropriate investment opportunities consistent with our investment objectives and market conditions.

We anticipate that substantially all of the net proceeds of this offering will be utilized in the manner described above within three months of receiving proceeds from this offering. Pending such utilization, we intend to invest the net proceeds of this offering primarily in cash, cash equivalents, U.S. government securities, and other high-quality debt investments that mature in one year or less from the date of investment, consistent with the requirements for continued qualification as a RIC for federal income tax purposes. These temporary investments may have lower yields than our other investments and, accordingly, may result in lower distributions, if any, during such period. Our ability to achieve our investment objective may be limited to the extent that the net proceeds from an offering, pending full investment, are held in lower yielding interest-bearing deposits or other short-term instruments.

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PRICE RANGE OF COMMON STOCK AND DISTRIBUTIONS

We currently intend to distribute in the form of cash distributions, up to 100% of our Investment Company Taxable Income, if any, to our stockholders in the form of monthly distributions. We may retain net long-term capital gains in excess of net short-term capital losses, retain and treat them as deemed distributions for tax purposes, or may distribute such amounts as supplemental distributions. The tax characteristics of distributions are reported annually to each stockholder on IRS Form 1099-DIV. There is no assurance that we will achieve investment results or maintain a tax status that will permit any specified level of cash distributions or year-to-year increases in cash distributions. At the option of a holder of record of common stock, all cash distributions with respect to shares of our common stock can be reinvested automatically under the dividend reinvestment plan. A stockholder whose shares of our common stock are held in the name of a broker or other nominee should contact the broker or nominee regarding participation in the dividend reinvestment plan on the stockholder’s behalf. See “Risk Factors—Risks Related to Our Regulation and Structure—We will be subject to corporate-level tax if we are unable to satisfy Code requirements for RIC qualification”; “Dividend Reinvestment Plan”; and “Material U.S. Federal Income Tax Considerations” in the accompanying prospectus.

Common shares of closed-end investment companies, including BDCs, frequently trade at a discount to their NAV per share. The possibility that our common shares may trade at such discount to our NAV per share is separate and distinct from the risk that our NAV per share may decline. We cannot predict whether our common shares will trade at prices above, at or below our NAV per share, although during the past two years, our common stock has frequently traded, and at times significantly, below NAV.

COMMON SHARE PRICE DATA

Our common stock is traded on Nasdaq under the symbol “GAIN.” The following table reflects, by quarter, the high and low intra-day sales prices per share of our common stock on Nasdaq, the intra-day sales prices as a percentage of NAV per share and distributions declared per share of our common stock for each fiscal quarter during the last two completed fiscal years and the current fiscal year through August 28, 2018.

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As of August 24, 2018, there were 22 record owners of our common stock.

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CONSOLIDATED SELECTED FINANCIAL DATA

The following consolidated selected financial data as of and for the fiscal years ended March 31, 2018, 2017, 2016, 2015 and 2014 are derived from our consolidated financial statements that have been audited by PricewaterhouseCoopers, LLP, an independent registered public accounting firm. The consolidated selected financial data for the three months ended June 30, 2018 and 2017 are derived from our unaudited consolidated financial statements included in this prospectus supplement. The “other unaudited data” included following the table below is also unaudited. The data should be read in conjunction with our consolidated financial statements and notes thereto and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included elsewhere in this prospectus supplement and the accompanying prospectus.

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SELECTED QUARTERLY FINANCIAL DATA

(UNAUDITED)

The following tables set forth certain quarterly financial data for each of the eight quarters in the two years ended March 31, 2018 and the first quarter of the fiscal year ending March 31, 2019. The data was derived from our unaudited consolidated financial statements. Results for any quarter are not necessarily indicative of results for the past fiscal year or for any future quarter.

(DOLLAR AMOUNTS IN THOUSANDS, EXCEPT PER SHARE DATA)

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MANAGEMENT’S DISCUSSION AND ANALYSIS OF

FINANCIAL CONDITION AND RESULTS OF OPERATIONS

The following analysis of our financial condition and results of operations should be read in conjunction with our Consolidated Financial Statements and the notes thereto contained elsewhere in this prospectus supplement and the accompanying prospectus. Historical financial condition and results of operations and percentage relationships among any amounts in the financial statements are not necessarily indicative of financial condition or results of operations for any future periods. Except per share amounts or unless otherwise indicated, dollar amounts in the tables included herein are in thousands.

OVERVIEW

General

We were incorporated under the General Corporation Laws of the State of Delaware on February 18, 2005. On June 22, 2005, we completed our initial public offering and commenced operations. We operate as an externally managed, closed-end, non-diversified management investment company and have elected to be treated as a BDC under the 1940 Act. For federal income tax purposes, we have elected to be treated as a RIC under Subchapter M of the Code. To continue to qualify as a RIC for federal income tax purposes and obtain favorable RIC tax treatment, we must meet certain requirements, including certain minimum distribution requirements. From our initial public offering in 2005 through June 30, 2018, we have made 156 consecutive monthly distributions to common stockholders.

We are externally managed by the Adviser, an affiliate of ours and an SEC registered investment adviser, pursuant to the Advisory Agreement. We have also entered into the Administration Agreement with the Administrator, an affiliate of ours and the Adviser. Each of the Adviser and the Administrator are privately-held companies that are indirectly owned and controlled by David Gladstone, our chairman and chief executive officer.

Additionally, Gladstone Securities, LLC (“Gladstone Securities”), a privately-held broker-dealer registered with the Financial Industry Regulatory Authority and insured by the Securities Investor Protection Corporation, which is indirectly owned and controlled by Mr. Gladstone, our chairman and chief executive officer, has provided other services, such as investment banking and due diligence services, to certain of our portfolio companies, for which Gladstone Securities receives a fee. Any such fees paid by portfolio companies to Gladstone Securities do not impact the fees we pay to the Adviser or the non-contractual, unconditional, and irrevocable credits against the base management fee. For additional information refer to Note 4—Related Party Transactions in the accompanying Notes to Consolidated Financial Statements.

We were established for the purpose of investing in debt and equity securities of established private businesses operating in the United States (“U.S.”). Our investment objectives are to: (i) achieve and grow current income by investing in debt securities of established businesses that we believe will provide stable earnings and cash flow to pay expenses, make principal and interest payments on our outstanding indebtedness, and make distributions to our stockholders that grow over time; and (ii) provide our stockholders with long-term capital appreciation in the value of our assets by investing in equity securities, generally in combination with the aforementioned debt securities, of established businesses that we believe can grow over time to permit us to sell our equity investments for capital gains. To achieve our objectives, our investment strategy is to invest in several categories of debt and equity securities, with individual investments generally totaling up to $30 million, although investment size may vary depending upon our total assets or available capital at the time of investment. We intend that our investment portfolio over time will consist of approximately 75% in debt securities and 25% in equity securities, at cost. As of June 30, 2018, our investment portfolio was made up of 74.2% in debt securities and 25.8% in equity securities, at cost.

We focus on investing in Lower Middle Market private businesses (which we generally define as companies with annual EBITDA of $3 million to $20 million) in the U.S. that meet certain criteria, including, but not limited to,

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the following: the sustainability of the business’ free cash flow and its ability to grow it over time, adequate assets for loan collateral, experienced management teams with a significant ownership interest in the portfolio company, reasonable capitalization of the portfolio company, including an ample equity contribution or cushion based on prevailing enterprise valuation multiples, and the potential to realize appreciation and gain liquidity in our equity position, if any. We anticipate that liquidity in our equity position will be achieved through a merger or acquisition of the portfolio company, a public offering of the portfolio company’s stock, or, to a lesser extent, by exercising our right to require the portfolio company to repurchase our warrants, though there can be no assurance that we will always have these rights. We invest in portfolio companies that need funds for growth capital or to finance acquisitions or recapitalize or, to a lesser extent, refinance their existing debt facilities. We seek to avoid investing in high-risk, early-stage enterprises.

We invest by ourselves or jointly with other funds and/or management of the portfolio company, depending on the opportunity. In July 2012, the SEC granted us the Co-Investment Order that expanded our ability to co-invest, under certain circumstances, with certain of our affiliates, including Gladstone Capital and any future business development company or closed-end management investment company that is advised (or sub-advised if it controls the fund) by the Adviser, or any combination of the foregoing, subject to the conditions in the Co-Investment Order. Since 2012, we have opportunistically made several co-investments with Gladstone Capital pursuant to the Co-Investment Order. We believe the Co-Investment Order has enhanced and will continue to enhance our ability to further our investment objectives and strategies. If we are participating in an investment with one or more co-investors, whether or not an affiliate of ours, our investment is likely to be smaller than if we were investing alone.

Our shares of common stock, Series B Term Preferred Stock, Series C Term Preferred Stock, Series D Term Preferred Stock and Series E Term Preferred Stock are traded on Nasdaq under the trading symbols “GAIN,” “GAINO,” “GAINN” “GAINM” and “GAINL,” respectively.

Business

Portfolio Activity

While the business environment remains competitive, we continue to see new investment opportunities consistent with our investment strategy of providing a combination of debt and equity in support of management and independent sponsor-led buyouts of Lower Middle Market companies in the U.S. During the three months ended June 30, 2018, we exited one portfolio company with a fair value prior to its sale of $28.1 million and invested $29.2 million in one new portfolio company, resulting in no net change in the number of companies in our portfolio, which was comprised of 33 companies as of June 30, 2018. From our initial public offering in June 2005 through June 30, 2018, we have made investments in 48 companies, excluding investments in syndicated loans, for a total of approximately $1 billion, before giving effect to principal repayments and divestitures.

The majority of the debt securities in our portfolio have a success fee component, which enhances the yield on our debt investments. Unlike PIK income, we generally do not recognize success fees as income until payment has been received. Due to the contingent nature of success fees, there are no guarantees that we will be able to collect any or all of these success fees or know the timing of any such collections. As a result, as of June 30, 2018, we had unrecognized, contractual success fees of $29.3 million, or $0.89 per common share. Consistent with GAAP, we generally have not recognized success fee receivables and related income in our Consolidated Financial Statements until earned.

From inception through June 30, 2018, we have completed 13 sales of portfolio companies that we acquired under our buyout strategy (which excludes investments in syndicated loans). In the aggregate, these sales have generated $99.8 million in net realized gains and $22.1 million in other income upon exit, for a total increase to our net assets of $121.9 million. We believe each of these transactions was an equity-oriented investment success and exemplifies our investment strategy of striving to achieve returns through current income on the debt portion

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of our investments and capital gains from the equity portion. The 13 liquidity events have offset any realized losses since inception, which were primarily incurred during the recession in connection with the sale of performing syndicated loans at a realized loss to pay off a former lender. These successful exits, in part, enabled us to increase the monthly distribution by 67.5% from March 2011 through June 30, 2018, and allowed us to declare and pay a $0.03 per common share supplemental distribution in fiscal year 2012, a $0.05 per common share supplemental distribution in November 2013, a $0.05 per common share supplemental distribution in December 2014, and a $0.06 per common share supplemental distribution in each of June 2017, December 2017, and June 2018.

Capital Raising Efforts

We have been able to meet our capital needs through extensions of and increases to the Credit Facility, and by accessing the capital markets in the form of public offerings of common and preferred stock. We have successfully extended the Credit Facility’s revolving period multiple times, most recently to November 2019, and currently have a total commitment amount of $165.0 million (with a potential total commitment of $250.0 million through additional commitments of new or existing lenders). During the three months ended June 30, 2018, we sold 168,824 shares of our common stock under our at-the-market program for gross proceeds of approximately $1.9 million. During the year ended March 31, 2018, we sold 127,412 shares of our common stock under our at-the-market program for gross proceeds of approximately $1.3 million. Additionally, we issued approximately 2.3 million shares of common stock for gross proceeds of $21.2 million in May 2017, inclusive of the June 2017 over-allotment. Refer to “Liquidity and Capital Resources—Revolving Line of Credit” for further discussion of the Credit Facility, “Liquidity and Capital Resources—Equity—Common Stock” and “Liquidity and Capital Resources—Equity—Term Preferred Stock” for further discussion of our common stock and mandatorily redeemable preferred stock. See “Prospectus Supplement Summary—Recent Developments” of this prospectus supplement for a discussion of our recent capital raising activities completed subsequent to the quarter ended June 30, 2018.

Although we have been able to access the capital markets historically, market conditions may continue to affect the trading price of our common stock and thus our ability to finance new investments through the issuance of common equity. On July 31, 2018, the closing market price of our common stock was $11.30 per share, representing a 2.3% discount to our NAV of $11.57 per share as of June 30, 2018. When our common stock trades below NAV, our ability to issue additional equity is constrained by provisions of the 1940 Act, which generally prohibits the issuance and sale of our common stock at an issuance price below the then-current NAV per share without stockholder approval, other than through sales to our then-existing stockholders pursuant to a rights offering.

At our 2017 Annual Meeting of Stockholders held on August 24, 2017, our stockholders approved a proposal authorizing us to issue and sell shares of our common stock at a price below our then-current NAV per share, subject to certain limitations, including that the number of common shares issued and sold pursuant to such authority does not exceed 25.0% of our then-outstanding common stock immediately prior to each such sale, provided that our board of directors (“Board of Directors”) makes certain determinations prior to any such sale. At our 2018 Annual Meeting of Stockholders held on August 2, 2018, our stockholders voted to approve a similar proposal, which is effective for one year from such date of approval. We sought and obtained stockholder approval concerning similar proposals at each Annual Meeting of Stockholders since 2008, and with our Board of Directors’ subsequent approval, we issued shares of our common stock in three offerings at a price below the then-current NAV per share, once in May 2017, once in March 2015, and once in October 2012. Certain sales of common stock under the at-the-market program in March and April 2018 were also below the then-current estimated NAV per share. The resulting proceeds, in part, have allowed us to (i) grow our portfolio by making new investments, (ii) generate additional income through these new investments, (iii) ensure continued compliance with regulatory tests and (iv) increase our debt capital while still complying with our applicable debt-to-equity ratios. Refer to “Liquidity and Capital Resources—Equity—Common Stock” for further discussion of our common stock.

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Regulatory Compliance

Our ability to seek external debt financing, to the extent that it is available under current market conditions, is further subject to the asset coverage limitations of the 1940 Act, which require us to have asset coverage (as defined in Sections 18 and 61 of the 1940 Act, as amended), of at least 200% (currently) (or 150.0%, effective April 10, 2019, unless earlier approved by our stockholders) on each of our senior securities representing indebtedness and our senior securities that are stock (such as our Term Preferred Stock).

On April 10, 2018, our Board of Directors, including a “required majority” (as such term is defined in Section 57(o) of the 1940 Act) thereof, approved the modified asset coverage requirements set forth in Section 61(a)(2) of the 1940 Act, as amended by the Small Business Credit Availability Act. As a result, the Company’s asset coverage requirements for senior securities will be changed from 200% to 150%, effective one year after the date of the Board of Directors’ approval, or April 10, 2019. Under the current 200% asset coverage standard, we may borrow debt or issue senior securities that are stock in the amount of $1.00 for every $1.00 of equity in the Company. Starting from April 10, 2019, under the 150% asset coverage standard, we may borrow debt or issue senior securities that are stock in the amount of $2.00 for every $1.00 of equity in the Company. Notwithstanding the modified asset coverage requirement under the 1940 Act, as amended, described above, we are separately subject to a minimum asset coverage requirement of 200% with respect to certain provisions of our Credit Facility and our outstanding Term Preferred Stock.

As of June 30, 2018, our asset coverage on our senior securities representing indebtedness was 566.8% and our asset coverage on our senior securities that are stock was 250.2%.

Investment Highlights

During the three months ended June 30, 2018, and inclusive of non-cash transactions, we invested $29.2 million in one new portfolio company, received $32.1 million in proceeds from repayments and sales, and extended $0.9 million of follow-on investments to existing portfolio companies through revolver draws and term loans.

Investment Activity

During the three months ended June 30, 2018, the following significant transactions occurred:

The following significant investment activity occurred subsequent to June 30, 2018. Also refer to Note 13—Subsequent Events in the accompanying Notes to Consolidated Financial Statements included elsewhere in this prospectus supplement.

Recent Developments

Registration Statement

On June 5, 2018, we filed a registration statement on Form N-2 (File No. 333-225447), which the SEC declared effective on July 13, 2018. The registration statement permits us to issue, through one or more transactions, up to

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an aggregate of $300.0 million in securities, consisting of common stock, preferred stock, subscription rights, debt securities, and warrants to purchase common stock, preferred stock, or debt securities, including through concurrent, separate offerings of such securities. As of July 31, 2018, we had the ability to issue up to $300.0 million in securities under the registration statement.

At-the-Market Program

In February 2018, we entered into sales agreements (commonly referred to as “at-the-market” (“ATM”) programs) with Cantor Fitzgerald & Co. (“Cantor”), Ladenburg Thalmann & Co., Inc., and Wedbush Securities Inc. (each a “Sales Agent”), under which we have the ability to issue and sell shares of our common stock, from time to time, through the Sales Agents, up to an aggregate offering price of $35.0 million. Pursuant to our prior registration statement on Form N-2 (File No. 333-204996), during the three months ended June 30, 2018, we sold 168,824 shares of our common stock under the ATM program with Cantor at a weighted-average gross price of $11.09 per share and raised approximately $1.9 million of gross proceeds. The weighted-average net price per share, after deducting commissions and offering costs borne by us, was $10.87 and resulted in total net proceeds of approximately $1.8 million. Certain of these sales were below our then-current estimated NAV per share during the sales period, with a discount of $0.002 per share, when comparing the sales price per share, after deducting commissions, to the then-current estimated NAV per share; however, the net dilutive effect (after commissions and offering costs borne by us) of these sales was $0.00 per common share as a result of the small number of shares sold at a slight discount to NAV per share and resulting rounding. In aggregate, the sales during the three months ended June 30, 2018 were above our then-current estimated NAV per share. As of June 30, 2018, we had remaining capacity to sell up to $31.8 million of common stock under the ATM program pursuant to this prospectus supplement and the accompanying prospectus.

Distributions and Dividends

In July 2018, our Board of Directors declared the following monthly distributions to common stockholders and monthly dividends to holders of our Series B Term Preferred Stock, Series C Term Preferred Stock and Series D Term Preferred Stock:

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RESULTS OF OPERATIONS

Comparison of the Three Months Ended June 30, 2018 to the Three Months Ended June 30, 2017

NM = Not Meaningful

Investment Income

Total investment income increased by 13.8% for the three months ended June 30, 2018, as compared to the prior year period. This increase was primarily due to an increase in interest income, partially offset by a decline in dividend, success fee, and other income, for the three months ended June 30, 2018, as compared to the prior year period.

Interest income from our investments in debt securities increased 23.9% for the three months ended June 30, 2018, as compared to the prior year period. Generally, the level of interest income from investments is directly related to the principal balance of our interest-bearing investment portfolio outstanding during the period multiplied by the weighted-average yield. The weighted-average principal balance of our interest-bearing investment portfolio during the three months ended June 30, 2018 was $409.9 million, compared to $340.5 million for the prior year period. This increase was primarily due to $71.4 million in new debt investments and

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$59.4 million in follow-on debt investments to existing portfolio companies originated after June 30, 2017 and $25.2 million of loans placed back on accrual status, partially offset by the pay-off or restructure of $57.7 million of debt investments and $55.1 million of loans placed on non-accrual status, and their respective impact on the weighted-average principal balance when considering timing of new investments, pay-offs, restructures, and non-accruals, as applicable. The weighted-average yield on our interest-bearing investments, excluding cash and cash equivalents and receipts recorded as dividend, success fee, and other income, was 13.0% for the three months ended June 30, 2018, compared to 12.6% for the prior year period. The weighted-average yield may vary from period to period, based on the current stated interest rate on interest-bearing investments.

At June 30, 2018, certain of our loans to three portfolio companies, B-Dry, LLC, The Mountain Corporation, and PSI Molded Plastics, Inc., were on non-accrual status, with an aggregate debt cost basis of $55.1 million. At June 30, 2017, certain of our loans to three portfolio companies, Alloy Die Casting Co., Precision Southeast, Inc., and Tread Corporation, were on non-accrual status, with an aggregate debt cost basis of $25.2 million.

Dividend, success fee, and other income for the three months ended June 30, 2018 decreased 23.8% from the prior year period. During the three months ended June 30, 2018, dividend, success fee, and other income primarily consisted of $2.1 million of success fee income and $0.1 million of dividend income. During the three months ended June 30, 2017, dividend, success fee, and other income primarily consisted of $2.0 million of success fee income and $0.9 million of dividend income.

The following table lists the investment income for our five largest portfolio company investments, at fair value, during the respective periods:

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Expenses

Total expenses, net of any non-contractual, unconditional, and irrevocable credits from the Adviser, increased 88.7% during the three months ended June 30, 2018, as compared to the prior year period, primarily as a result of an increase in the capital gains-based incentive fee, interest expense, and the base management fee, partially offset by an increase in non-contractual, unconditional, and irrevocable credits from the Adviser.

In accordance with GAAP, we recorded a capital gains-based incentive fee of $6.5 million during the three months ended June 30, 2018, which is not yet contractually due. There was no capital gains-based incentive fee during the prior year period.

The base management fee increased for the three months ended June 30, 2018, as compared to the prior year period, as average total assets increased over the respective periods as a result of an increase in investments.

The base management fee, loan servicing fee, incentive fee, and their related non-contractual, unconditional, and irrevocable credits are computed quarterly, as described under “Transactions with the Adviser” in Note 4—Related Party Transactions in the accompanying Notes to Consolidated Financial Statements and are summarized in the following table:

Interest and dividend expense increased 34.0% during the three months ended June 30, 2018, as compared to the prior year period, due to a higher weighted-average balance outstanding on the Credit Facility, partially offset by a lower effective interest rate. The weighted-average balance outstanding on the Credit Facility during the three

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months ended June 30, 2018 was $123.3 million, as compared to $42.1 million in the prior year period. The effective interest rate on the Credit Facility, excluding the impact of deferred financing costs, during the three months ended June 30, 2018 was 5.4%, as compared to 6.1% in the prior year period.

Realized and Unrealized Gain (Loss)

Net Realized Gain on Investments

During the three months ended June 30, 2018, we recorded net realized gains on investments of $14.1 million, primarily related to a $13.8 million realized gain from the exit of Drew Foam, as compared to net realized gains on investments of $1.2 million during the prior year period, primarily related to a $1.0 million realized gain from the exit of Mitchell Rubber Products, Inc.

Net Unrealized Appreciation (Depreciation) of Investments

During the three months ended June 30, 2018, we recorded net unrealized appreciation of investments of $18.1 million. The realized gains (losses) and unrealized appreciation (depreciation) across our investments for the three months ended June 30, 2018, were as follows:

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The primary drivers of net unrealized appreciation of $18.1 million for the three months ended June 30, 2018, were increased performance of certain of our portfolio companies and an increase in comparable multiples used to estimate the fair value of certain of our portfolio companies, which were partially offset by the reversal of previously recorded unrealized appreciation upon the exit of our investment in Drew Foam and a decline in performance of certain of our other portfolio companies.

During the three months ended June 30, 2017, we recorded net unrealized appreciation of investments of $1.5 million. The realized gains (losses) and unrealized appreciation (depreciation) across our investments for the three months ended June 30, 2017, were as follows:

The primary drivers of net unrealized appreciation of $1.5 million for the three months ended June 30, 2017, were increased performance of certain of our portfolio companies and an increase in comparable multiples used to estimate the fair value of certain of our portfolio companies, which were partially offset by a decline in performance of certain of our other portfolio companies.

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Across our entire investment portfolio, we recorded $0.5 million of net unrealized depreciation on our debt positions and $18.6 million of net unrealized appreciation on our equity positions for the three months ended June 30, 2018. At June 30, 2018, the fair value of our investment portfolio was greater than our cost basis by $32.4 million, as compared to $14.3 million at March 31, 2018, representing net unrealized appreciation of $18.1 million for the three months ended June 30, 2018. Our entire portfolio had a fair value of 105.4% of cost as of June 30, 2018.

Net Unrealized Depreciation on Other

During the three months ended June 30, 2018, we recorded net unrealized depreciation of other of $0.1 million related to the Credit Facility recorded at fair value. There was no unrealized appreciation or depreciation on other during the three months ended June 30, 2017.

LIQUIDITY AND CAPITAL RESOURCES

Operating Activities

Net cash provided by operating activities for the three months ended June 30, 2018 was $10.7 million, as compared to $26.3 million for the three months ended June 30, 2017. This change was primarily due to an increase in the purchase of investments, partially offset by higher repayments and net proceeds from the sale of investments period over period.

Purchases of investments were $30.1 million during the three months ended June 30, 2018, compared to $2.1 million during the three months ended June 30, 2017. Repayments and net proceeds from the sale of investments totaled $32.1 million during the three months ended June 30, 2018, compared to $19.5 million during the three months ended June 30, 2017.

As of June 30, 2018, we had equity investments in or loans to 33 portfolio companies with an aggregate cost basis of $596.9 million. As of June 30, 2017, we had equity investments in or loans to 33 portfolio companies with an aggregate cost basis of $508.8 million. The following table summarizes our total portfolio investment activity during the three months ended June 30, 2018 and 2017:

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The following table summarizes the contractual principal repayment and maturity of our investment portfolio by fiscal year, assuming no voluntary prepayments, as of June 30, 2018:

Financing Activities

Net cash used in financing activities for the three months ended June 30, 2018 was $11.3 million, which consisted primarily of $4.5 million of net repayments on the Credit Facility and $8.6 million in distributions to common stockholders, partially offset by $1.8 million of net proceeds from the issuance of common stock under the ATM program.

Net cash used in financing activities for the three months ended June 30, 2017 was $23.7 million, which consisted primarily of $35.7 million of net repayments on the Credit Facility and $8.0 million in distributions to common stockholders, partially offset by $20.1 million of net proceeds from the issuance of common stock in May 2017, including the partial exercise of the underwriters’ over-allotment option in June 2017.

Distributions and Dividends to Stockholders

Common Stock Distributions

To qualify to be taxed as a RIC and thus avoid corporate level federal income tax on the income we distribute to our stockholders, we are required to distribute to our stockholders on an annual basis at least 90% of our taxable ordinary income plus the excess of our net short-term capital gains over net long-term capital losses (“Investment Company Taxable Income”). Additionally, the Credit Facility generally restricts the amount of distributions to stockholders that we can pay out to be no greater than the sum of certain amounts, including, but not limited to, our net investment income, plus net capital gains, plus amounts elected by the Company to be considered as having been paid during the prior fiscal year in accordance with Section 855(a) of the Code. In accordance with these requirements, our Board of Directors declared, and we paid, monthly cash distributions of $0.067 per common share for each of the three months from April through June 2018 and a supplemental distribution of $0.06 per common share for June 2018.

The federal income tax characteristics of distributions paid to our common stockholders is generally reported to stockholders on Internal Revenue Service Form 1099 after the end of the calendar year based on tax information for the full fiscal year. Any characterization made on an interim, quarterly basis may not be representative of the actual tax characterization for the full year.

For the year ended March 31, 2018, distributions to common stockholders totaled $28.9 million and were less than our taxable income for the same year, after also taking into account spillover amounts under Section 855(a) of the Code with respect to the prior year. At March 31, 2018, we elected to treat $8.4 million of the first

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distributions paid after fiscal year-end as having been paid in the prior fiscal year, in accordance with Section 855(a) of the Code. In addition, for the year ended March 31, 2018, we recorded $1.6 million of net estimated adjustments for permanent book-tax differences to reflect tax character, which decreased Capital in excess of par value and Accumulated net realized gain in excess of distributions and increased Net investment income in excess of distributions on our accompanying Consolidated Statements of Assets and Liabilities. For the three months ended June 30, 2018, we recorded $0.7 million of net estimated adjustments for permanent book-tax differences to reflect tax character, which decreased Capital in excess of par value and Accumulated net realized gain in excess of distributions and increased Overdistributed net investment income on our accompanying Consolidated Statements of Assets and Liabilities.

Preferred Stock Dividends

Our Board of Directors declared and we paid monthly cash dividends of (i) $0.140625 per share to holders of our Series B Term Preferred Stock, (ii) $0.135417 per share to holders of our Series C Term Preferred Stock, and (iii) $0.13020833 per share to holders of our Series D Term Preferred Stock for each of the three months from April through June 2018. In accordance with GAAP, we treat these monthly dividends as an operating expense. The federal income tax characteristics of dividends paid to our preferred stockholders generally constitute ordinary income or capital gains to the extent of our current and accumulated earnings and profits and is reported after the end of the calendar year based on tax information for the full fiscal year. Such a characterization made on an interim, quarterly basis may not be representative of the actual tax characterization for the full year.

Dividend Reinvestment Plan

Our common stockholders who hold their shares through our transfer agent, Computershare, Inc. (“Computershare”), have the option to participate in a dividend reinvestment plan offered by Computershare, as the plan agent. This is an “opt in” dividend reinvestment plan, meaning that common stockholders may elect to have their cash distributions automatically reinvested in additional shares of our common stock. Common stockholders who do not make such election will receive their distributions in cash. Common stockholders who receive distributions in the form of stock will be subject to the same federal, state and local tax consequences as stockholders who elect to receive their distributions in cash. The common stockholder will have an adjusted basis in the additional common shares purchased through the plan equal to the amount of the reinvested distribution. The additional shares will have a new holding period commencing on the day following the date on which the shares are credited to the common stockholder’s account. Computershare purchases shares in the open market in connection with the obligations under the plan. The Computershare dividend reinvestment plan is not open to holders of our preferred stock.

Equity

Registration Statement

On June 5, 2018, we filed a registration statement on Form N-2 (File No. 333-225447), which the SEC declared effective on July 13, 2018. The registration statement permits us to issue, through one or more transactions, up to an aggregate of $300.0 million in securities, consisting of common stock, preferred stock, subscription rights, debt securities, and warrants to purchase common stock, preferred stock, or debt securities, including through concurrent, separate offerings of such securities. As of July 31, 2018, we had the ability to issue up to $300.0 million in securities under the registration statement.

Common Stock

In February 2018, we entered into equity distribution agreements with Sales Agents, under which we have the ability to issue and sell shares of our common stock, from time to time, through the Sales Agents, up to an aggregate offering price of $35.0 million. Pursuant to our prior registration statement on Form N-2 (File No. 333-204996), during the three months ended June 30, 2018, we sold 168,824 shares of our common

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stock under the ATM program with Cantor at a weighted-average gross price of $11.09 per share and raised approximately $1.9 million of gross proceeds. The weighted-average net price per share, after deducting commissions and offering costs borne by us, was $10.87 and resulted in total net proceeds of approximately $1.8 million. Certain of these sales were below our then-current estimated NAV per share during the sales period, with a discount of $0.002 per share, when comparing the sales price per share, after deducting commissions, to the then-current estimated NAV per share; however, the net dilutive effect (after commissions and offering costs borne by us) of these sales was $0.00 per common share as a result of the small number of shares sold at a slight discount to NAV per share and resulting rounding. In aggregate, the sales during the three months ended June 30, 2018 were above our then-current estimated NAV per share. As of July 31, 2018, we had remaining capacity to sell up to $31.8 million of common stock under the ATM program.

Pursuant to our prior registration statement on Form N-2 (File No. 333-204996), in March 2018, we sold 127,412 shares of our common stock under the ATM program with Cantor at a weighted-average gross price of $10.45 per share and raised approximately $1.3 million of gross proceeds. The weighted-average net price per share, after deducting commissions and offering costs borne by us, was $10.24 and resulted in total net proceeds of approximately $1.3 million. These sales were below our then-current estimated NAV per share during the sales period, with such discounts ranging from $0.01 per share to $0.07 per share, when comparing the sales price per share, after deducting commissions, to the then-current estimated NAV per share; however, the net dilutive effect (after commissions and offering costs borne by us) of these sales was $0.00 per common share as a result of the small number of shares sold at a slight discount to NAV per share and resulting rounding.

Also pursuant to our prior registration statement on Form N-2 (File No. 333-204996), in May 2017, we completed a public offering of 2.1 million shares of our common stock at a public offering price of $9.38 per share, which was below our then-current NAV of $9.95 per share. Gross proceeds totaled $19.7 million and net proceeds, after deducting underwriting discounts and commissions and offering costs borne by us, were $18.7 million, which were used to repay borrowings under the Credit Facility and for other general corporate purposes. In June 2017, the underwriters partially exercised their over-allotment option and purchased an additional 155,265 shares at the public offering price of $9.38 per share and on the same terms and conditions solely to cover over-allotments, which resulted in gross proceeds of $1.5 million and net proceeds, after deducting underwriting discounts and commissions and offering costs borne by us, of $1.4 million.

We anticipate issuing equity securities to obtain additional capital in the future. However, we cannot determine the timing or terms of any future equity issuances or whether we will be able to issue equity on terms favorable to us, or at all. When our common stock is trading at a price below NAV per share, the 1940 Act places regulatory constraints on our ability to obtain additional capital by issuing common stock. Generally, the 1940 Act provides that we may not issue and sell our common stock at a price below our NAV per common share, other than to our then-existing common stockholders pursuant to a rights offering, without first obtaining approval from our stockholders and our independent directors and meeting other stated requirements. On July 31, 2018, the closing market price of our common stock was $11.30 per share, representing a 2.3% discount to our NAV per share of $11.57 as of June 30, 2018. At our 2017 Annual Meeting of Stockholders held on August 24, 2017, our stockholders approved a proposal authorizing us to issue and sell shares of our common stock at a price below our then-current NAV per common share for a period of one year from the date of such approval, provided that our Board of Directors makes certain determinations prior to any such sale. At our 2018 Annual Meeting of Stockholders held on August 2, 2018, our stockholders voted to approve a similar proposal, which is effective for one year from such date of approval.

Term Preferred Stock

Pursuant to an earlier registration statement on Form N-2 (Registration No. 333-181879), in November 2014, we completed a public offering of 1,656,000 shares of our Series B Term Preferred Stock at a public offering price of $25.00 per share. Gross proceeds totaled $41.4 million and net proceeds, after deducting underwriting

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discounts and offering costs borne by us, were $39.7 million. Total underwriting discounts and offering costs related to this offering were $1.7 million, which have been recorded as discounts to the liquidation value on our accompanying Consolidated Statements of Assets and Liabilities and are being amortized over the period ending December 31, 2021, the mandatory redemption date.

Our Series B Term Preferred Stock is not convertible into our common stock or any other security. Our Series B Term Preferred Stock provides for a fixed dividend equal to 6.75% per year, payable monthly (which equates to $2.8 million per year). We are required to redeem all shares of our outstanding Series B Term Preferred Stock on December 31, 2021, for cash at a redemption price equal to $25.00 per share, plus an amount equal to accumulated but unpaid dividends, if any, to, but excluding, the date of redemption. In addition, two other potential mandatory redemption triggers are as follows: (1) upon the occurrence of certain events that would constitute a change in control of us, we would be required to redeem all of our outstanding Series B Term Preferred Stock, and (2) if we fail to maintain asset coverage of at least 200%, we are required to redeem a portion of our outstanding Series B Term Preferred Stock or otherwise cure the asset coverage redemption trigger (and we may also redeem additional securities to cause the asset coverage to be 215%). We may also voluntarily redeem all or a portion of our Series B Term Preferred Stock at our sole option at the redemption price at any time.

Also, pursuant to an earlier registration statement on Form N-2 (Registration No. 333-181879), in May 2015, we completed a public offering of 1,610,000 shares of our Series C Term Preferred Stock at a public offering price of $25.00 per share. Gross proceeds totaled $40.3 million and net proceeds, after deducting underwriting discounts and offering costs borne by us, were $38.6 million. Total underwriting discounts and offering costs related to this offering were $1.6 million, which have been recorded as discounts to the liquidation value on our accompanying Consolidated Statements of Assets and Liabilities and are being amortized over the period ending May 31, 2022, the mandatory redemption date.

Our Series C Term Preferred Stock is not convertible into our common stock or any other security. Our Series C Term Preferred Stock provides for a fixed dividend equal to 6.50% per year, payable monthly (which equates to $2.6 million per year). We are required to redeem all shares of our outstanding Series C Term Preferred Stock on May 31, 2022, for cash at a redemption price equal to $25.00 per share, plus an amount equal to accumulated but unpaid dividends, if any, to, but excluding, the date of redemption. In addition, two other potential mandatory redemption triggers are as follows: (1) upon the occurrence of certain events that would constitute a change in control of us, we would be required to redeem all of our outstanding Series C Term Preferred Stock, and (2) if we fail to maintain asset coverage of at least 200%, we are required to redeem a portion of our outstanding Series C Term Preferred Stock or otherwise cure the asset coverage redemption trigger (and we may also redeem additional securities to cause the asset coverage to be 215%). We may also voluntarily redeem all or a portion of our Series C Term Preferred Stock at our sole option at the redemption price at any time.

Pursuant to our prior registration statement on Form N-2 (Registration No. 333-204996), in September 2016, we completed a public offering of 2,300,000 shares of our Series D Term Preferred Stock at a public offering price of $25.00 per share. Gross proceeds totaled $57.5 million and net proceeds, after deducting underwriting discounts and offering costs borne by us, were $55.4 million. Total underwriting discounts and offering costs related to this offering were $2.1 million, which have been recorded as discounts to the liquidation value on our accompanying Consolidated Statements of Assets and Liabilities and are being amortized over the period ending September 30, 2023, the mandatory redemption date.

Our Series D Term Preferred Stock is not convertible into our common stock or any other security. Our Series D Term Preferred Stock provides for a fixed dividend equal to 6.25% per year, payable monthly (which equates to $3.6 million per year). We are required to redeem all shares of our outstanding Series D Term Preferred Stock on September 30, 2023, for cash at a redemption price equal to $25.00 per share, plus an amount equal to accumulated but unpaid dividends, if any, to, but excluding, the date of redemption. In addition, two other potential mandatory redemption triggers are as follows: (1) upon the occurrence of certain events that would

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constitute a change in control of us, we would be required to redeem all of our outstanding Series D Term Preferred Stock, and (2) if we fail to maintain asset coverage of at least 200% and are unable to correct such failure within a specific amount of time, we are required to redeem a portion of our outstanding Series D Term Preferred Stock or otherwise cure the asset coverage redemption trigger (and we may also redeem additional securities to cause the asset coverage to be 240%). We may also voluntarily redeem all or a portion of our Series D Term Preferred Stock at our sole option at the redemption price at any time on or after September 30, 2018.

Each series of our mandatorily redeemable preferred stock has a preference over our common stock with respect to dividends, whereby no distributions are payable on our common stock unless the stated dividends, including any accrued and unpaid dividends, on the mandatorily redeemable preferred stock have been paid in full. The Series B Term Preferred Stock, Series C Term Preferred Stock, and Series D Term Preferred Stock are considered liabilities in accordance with GAAP and, as such, affect our asset coverage, exposing us to additional leverage risks. The asset coverage on our senior securities that are stock (our Series B Term Preferred Stock, Series C Term Preferred Stock, and Series D Term Preferred Stock) as of June 30, 2018 was 250.2%, calculated pursuant to Sections 18 and 61 of the 1940 Act. See “Prospectus Supplement Summary—Recent Developments” of this prospectus supplement for a discussion of our recent capital raising activities completed subsequent to the quarter ended June 30, 2018.

Revolving Line of Credit

On November 16, 2016, we, through our wholly-owned subsidiary, Business Investment, entered into Amendment No. 2 to the Fifth Amended and Restated Credit Agreement, originally entered into on April 30, 2013 and as previously amended on June 26, 2014, with KeyBank, as administrative agent, lead arranger, managing agent and lender, the Adviser, as servicer, and certain other lenders party thereto. The revolving period was extended to November 15, 2019, and if not renewed or extended by such date, all principal and interest will be due and payable on or before November 15, 2021 (two years after the revolving period end date). The amended Credit Facility provides a one-year extension option that may be exercised on or before the second anniversary of the November 16, 2016 amendment date, subject to approval by all lenders. Additionally, the Credit Facility commitment amount was changed from $185.0 million to $165.0 million and, subject to certain terms and conditions, can be expanded to a total facility amount of $250.0 million through additional commitments of existing or new lenders. Advances under the Credit Facility generally bear interest at 30-day LIBOR plus 3.15% per annum until November 15, 2019, with the margin then increasing to 3.40% for the period from November 15, 2019 to November 15, 2020, and increasing further to 3.65% thereafter. The Credit Facility has an unused commitment fee of 0.50% per annum on the portion of the total unused commitment amount that is less than or equal to 45.0% of the total commitment amount and 0.80% per annum on the total unused commitment amount that is greater than 45.0%. We incurred fees of approximately $1.4 million in connection with this amendment.

On January 20, 2017, we entered into Amendment No. 3 to the Credit Facility, which clarified a definition in the Company’s performance guaranty under the Credit Facility. See “Prospectus Supplement Summary—Recent Developments” of this prospectus supplement for a discussion of the latest amendment to the Credit Facility entered into subsequent to the quarter ended June 30, 2018.

Interest is payable monthly during the term of the Credit Facility. Available borrowings are subject to various constraints and applicable advance rates, which are generally based on the size, characteristics, and quality of the collateral pledged by Business Investment. The Credit Facility also requires that any interest and principal payments on pledged loans be remitted directly by the borrower into a lockbox account with KeyBank. KeyBank is also the trustee of the account and generally remits the collected funds to us once a month.

Among other things, the Credit Facility contains covenants that require Business Investment to maintain its status as a separate legal entity, prohibit certain significant corporate transactions (such as mergers, consolidations, liquidations or dissolutions) and restrict certain material changes to our credit and collection policies without the

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lenders’ consent. The Credit Facility also generally seeks to restrict distributions to stockholders to the sum of (i) our net investment income, (ii) net capital gains, and (iii) amounts deemed by the Company to be considered as having been paid during the prior fiscal year in accordance with Section 855(a) of the Code. Loans eligible to be pledged as collateral are subject to certain limitations, including, among other things, restrictions on geographic concentrations, industry concentrations, loan size, payment frequency and status, average life, portfolio company leverage, and lien property. The Credit Facility also requires Business Investment to comply with other financial and operational covenants, which obligate Business Investment to, among other things, maintain certain financial ratios, including asset and interest coverage and a minimum number of obligors required in the borrowing base. Additionally, the Credit Facility contains a performance guaranty that requires the Company to maintain (i) a minimum net worth (defined in the Credit Facility to include our mandatory redeemable term preferred stock) of the greater of $210.0 million or $210.0 million plus 50% of all equity and subordinated debt raised minus 50% of any equity or subordinated debt redeemed or retired after November 16, 2016, which equated to $222.2 million as of June 30, 2018, (ii) asset coverage with respect to senior securities representing indebtedness of at least 200% (or such higher percentage as may be set forth in Section 61 of the 1940 Act), and (iii) our status as a BDC under the 1940 Act and as a RIC under the Code. As of June 30, 2018, and as defined in the performance guaranty of the Credit Facility, we had a net worth of $514.7 million, asset coverage on our senior securities representing indebtedness of 566.8%, calculated in compliance with the requirements of Sections 18 and 61 of the 1940 Act, and an active status as a BDC and RIC. As of June 30, 2018, we had availability, after adjustments for various constraints based on collateral quality, of $59.5 million under the Credit Facility and were in compliance with all covenants under the Credit Facility. As of July 31, 2018, we had availability, before adjustments for various constraints based on collateral quality, of $62.0 million under the Credit Facility.

OFF-BALANCE SHEET ARRANGEMENTS

Unlike PIK income, we generally do not recognize success fees as income until payment has been received. Due to the contingent nature of success fees, there are no guarantees that we will be able to collect any or all of these success fees or know the timing of any such collections. As a result, as of June 30, 2018 and March 31, 2018, we had unrecognized, contractual off-balance sheet success fee receivables of $29.3 million and $28.3 million (or approximately $0.89 and $0.87 per common share), respectively, on our debt investments. Consistent with GAAP, we generally have not recognized success fee receivables and related income in our Consolidated Financial Statements until earned.

CONTRACTUAL OBLIGATIONS

We have line of credit and delayed draw term loan commitments to certain of our portfolio companies that have not been fully drawn. Since these line of credit and delayed draw term loan commitments have expiration dates and we expect many will never be fully drawn, the total line of credit and delayed draw term loan commitment amounts do not necessarily represent future cash requirements. We estimate the fair value of the combined unused line of credit and delayed draw term loan commitments as of June 30, 2018 to be immaterial.

We have also extended a guaranty on behalf of one of our portfolio companies, whereby we have guaranteed $2.0 million of obligations of Country Club Enterprises, LLC. The guaranty expires in February 2019, unless renewed. As of June 30, 2018, we have not been required to make payments on this or any previous guaranties, and we consider the credit risks to be remote and the fair value of this guaranty to be immaterial.

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The following table shows our contractual obligations as of June 30, 2018, at cost: