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): July 11, 2012

New Mountain Finance Corporation

(Exact name of registrant as specified in its charter)

787 7^th Avenue, 48^th Floor, New York, NY 10019

(Address of principal executive offices)

Registrant’s telephone number, including area code (212) 730-0300

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:

Set forth below are certain preliminary estimates of our financial condition and results of operations for the three months ended June 30, 2012. These estimates are subject to the completion of financial closing procedures and are not a comprehensive statement of our financial results for the three months ended June 30, 2012. We advise you that our actual results may differ materially from these estimates as a result of the completion of our financial closing procedures, final adjustments and other developments which may arise between now and the time that our financial results for the three months ended June 30, 2012 are finalized. This information is inherently uncertain.

Our net adjusted investment income per share for the three months ended June 30, 2012 is estimated to be between $0.34 and $0.35. Our net asset value per share as of June 30, 2012 is estimated to be between $13.80 and $13.85.

We currently expect to file our quarterly report on Form 10-Q on or about August 8, 2012 after the close of the financial markets. The preliminary financial estimates provided herein have been prepared by, and are the responsibility of, management. Deloitte & Touche LLP, our independent registered public accounting firm, has not audited, reviewed, compiled, or performed any procedures with respect to the accompanying preliminary financial data. Accordingly, Deloitte & Touche LLP does not express an opinion or any form of assurance with respect thereto.

The information disclosed under this Item 2.02 is being furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 and shall not be deemed incorporated by reference into any filing made under the Securities Act of 1933, except as expressly set forth by specific reference in such filing.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this Current Report on Form 8-K to be signed on its behalf by the undersigned hereunto duly authorized.