8-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event Reported): May 6, 2026

Gladstone Capital Corporation

(Exact Name of Registrant as Specified in Charter)

(703) 287-5800

(Registrant’s telephone number, including area code)

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR §230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2). Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

On May 6, 2026, Gladstone Capital Corporation issued a press release announcing its financial results for the fiscal quarter ended March 31, 2026. The text of the press release is included as an exhibit to this Current Report on Form 8-K. The information in this Current Report on Form 8-K, including Exhibit 99.1 attached hereto, is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, regardless of any general incorporation language in such filing.

(d) Exhibits.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EX-99.1

Exhibit 99.1

Gladstone Capital Corporation Reports Financial Results for its

Second Quarter Ended March 31, 2026

McLean, VA, May 6, 2026: Gladstone Capital Corporation (Nasdaq: GLAD) (the “Company”) today announced earnings for its second quarter ended March 31, 2026. Please read the Company’s Quarterly Report on Form 10-Q, filed today with the U.S. Securities and Exchange Commission (the “SEC”), which is available on the SEC’s website at www.sec.gov and the Investors section of the Company’s website at www.GladstoneCapital.com.

Summary Information (dollars in thousands, except per share data) (unaudited):

NM – not meaningful

Second Fiscal Quarter 2026 Highlights:

-1-

Second Fiscal Quarter 2026 Results:

Total investment income increased by $1.5 million, or 6.0%, for the quarter ended March 31, 2026, compared to the prior quarter ended December 31, 2025, driven primarily by a $2.2 million increase in other income, quarter over quarter, partially offset by a $0.7 million decrease in interest income, quarter over quarter. The decrease in interest income was driven mainly by a decrease in the weighted average yield to 11.8% during the quarter ended March 31, 2026, as compared to 12.2% during the quarter ended December 31, 2025 (due primarily to a decrease in average SOFR). This decreasing factor was offset by an increase in the weighted average principal balance of our interest-bearing investment portfolio to $794.0 million during the quarter ended March 31, 2026, as compared to $772.3 million during the quarter ended December 31, 2025, an increase of $21.7 million, or 2.8%. Other income increased by $2.2 million, or 354.6%, quarter over quarter primarily due to increases in dividend income and prepayment fee income, quarter over quarter.

Total expenses increased by $0.9 million, or 6.8%, quarter over quarter, primarily due to a $0.8 million increase in the net base management fee, driven by higher assets used to calculate the base management fee and lower deal origination fees which are credited to the base management fee.

Net investment income for the quarter ended March 31, 2026 was $11.8 million, or $0.52 per share.

The net increase in net assets resulting from operations was $15.5 million, or $0.68 per share, for the quarter ended March 31, 2026, compared to $5.5 million, or $0.24 per share, for the quarter ended December 31, 2025. The current quarter increase in net assets resulting from operations was primarily driven by $11.8 million of net investment income and $4.8 million of net unrealized appreciation, partially offset by $0.6 million of net realized loss recognized during the quarter.

Subsequent Events: Subsequent to March 31, 2026, the following significant events occurred:

-2-

Comments from Gladstone Capital’s CEO and President, Bob Marcotte: “The strength of our performance this quarter emanated from our lower middle market focus which supported the timely recycling of our invested capital while generating prepayment fees, as well as delivering equity distributions and appreciation from the organic growth and maturity of our modest equity exposure. Based on the current outlook for floating rates and prevailing spreads, we feel well positioned to sustain our distributions and deliver strong economic returns for our shareholders over the balance of 2026.”

Conference Call for Stockholders: The Company will hold its earnings release conference call on Thursday, May 7, 2026, at 8:30 a.m. Eastern Time. Please call (866) 424-3437 to enter the conference call. An operator will monitor the call and set a queue for any questions. A replay of the conference call will be available through May 14, 2026. To hear the replay, please dial (877) 660-6853 and use playback conference number 13759085. The replay of the conference call will be available beginning approximately one hour after the call concludes. The live audio broadcast of the Company’s quarterly conference call will also be available online at www.GladstoneCapital.com. The event will be archived and available for replay on the investors section of the Company’s website.

About Gladstone Capital Corporation: Gladstone Capital Corporation is a publicly-traded business development company that invests in debt and equity securities, consisting primarily of secured first and second lien term loans to lower middle market businesses in the United States. Information on the business activities of Gladstone Capital and the other publicly-traded Gladstone funds can be found at www.GladstoneCompanies.com.

To obtain a paper copy of the Company’s most recent Form 10-Q, please contact the Company at 1521 Westbranch Drive, Suite 100, McLean, VA 22102, ATTN: Investor Relations. The financial information above is not comprehensive and is without notes, so readers should obtain and carefully review the Company’s Form 10-Q for the quarter ended March 31, 2026, including the notes to the consolidated financial statements contained therein.

Investor Relations Inquiries: Please visit www.gladstonecompanies.com or (703) 287-5893.

Forward-looking Statements:

The statements inthis press release about future growth and shareholder returns are “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of1934, as amended. These forward-looking statements inherently involve certain risks and uncertainties in predicting future results and conditions. Although these statements are based on our current plans that are believed to be reasonable as ofthe date of this press release, a number of factors could cause actual results and conditions to differ materially from these forward-looking statements, including those factors described from time to time in our filings with the U.S. Securities andExchange Commission. The Company undertakes no obligation to publicly release the result of any revisions to these forward-looking statements that may be made to reflect any future events or otherwise, except as required by law.

-3-