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): March 19, 2021

CAPSTONE TURBINE CORPORATION

(Exact name of registrant as specified in its charter)

(818) 734-5300

(Registrant’s telephone number, including area code)

Former name or former address, if changed since last report: N/A

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:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

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 March 19, 2021, Capstone Turbine Corporation (the “Company”) entered into the second amendment (the “Amendment”) to the At The Market Offering Agreement (the “Agreement”), dated June 7, 2018, between the Company and H.C. Wainwright & Co., LLC (“Wainwright”). The Amendment modifies the Agreement to, among other things, reflect the Company’s filing of a new Registration Statement on Form S-3 (the “Shelf Registration Statement”) with the Securities and Exchange Commission on or about March 22, 2021 and set the maximum amount of shares of the Company’s common stock, par value $0.001 per share (“Common Stock”), that the Company may offer and sell through or to Wainwright from time to time under the Company’s at-the-market equity program following the effective date of the Shelf Registration Statement at $50,000,000, subject to certain limitations set forth in the Amendment.

This report shall not constitute an offer to sell or the solicitation of an offer to buy nor shall there be any sale of shares of Common Stock in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.

The foregoing description of the Amendment does not purport to be complete and is subject to, and qualified in its entirety by, the full text of the Amendment, which is filed herewith as Exhibit 10.1 to this Current Report and is incorporated by reference herein.

(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.