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Table of Contents ý UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 Commission File Number 814-00832 Annual Report Pursuant to Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 For the fiscal year ended December 31 , 2020 0 Transition Report Pursuant to Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 FORM 10 - K Exact name of registrant as specified in its charter , addresses of principal executive offices , telephone numbers and states or other jurisdictions of incorporation or organization New Mountain Finance Corporation 787 Seventh Avenue , 48th Floor New York , New York 10019 Telephone : ( 212 ) 720-0300 State of Incorporation : Delaware Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) NMFC NMFCL Title of each class Common stock , par value $ 0.01 per share 5.75 % Notes due 2023 Securities registered pursuant to Section 12 ( g ) of the Act : Title of each class None I.R.S. Employer Identification Number Name of each exchange on which registered The NASDAQ Global Select Market The NASDAQ Global Select Market 27-2978010 Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes ý No o Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes o No ý Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes ý No o Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( § 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes O No O Accelerated filer o Smaller reporting company o Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company or an emerging growth company . See definitions of " large accelerated filer " , " accelerated filer " , " smaller reporting company " and " emerging growth company " in Rule 12b - 2 of the Exchange Act : Large accelerated filer ý Non - accelerated filer o Emerging growth company o 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 . O