FORM10-Q ýQuarterly Report Pursuant to Section13 or 15(d)of the Securities Exchange Act of 1934For the Quarterly Period EndedJune30, 2025 Transition Report Pursuant to Section13 or 15(d)of the Securities Exchange Act of 1934 Exactnameofregistrantasspecifiedinitscharter,addressofprincipalexecutiveoffices,telephonenumbersandstatesorotherjurisdictionsofincorporationororganizationNew Mountain Finance Corporation I.R.S.EmployerIdentificationNumber 27-2978010 1633 Broadway, 48thFloorNew York,New York10019Telephone: (212)720-0300State of Incorporation:Delaware Indicate by check mark whether the registrant (1)has filed all reports required to be filed by Section13 or 15(d)of the Securities ExchangeAct of 1934 (the "Exchange Act") during the preceding 12 months (or for such shorter period that the registrant was required to file suchreports), and (2)has been subject to such filing requirements for the past 90 days.YesýNoo Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant toRule405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant wasrequired to submit such files).YesýNoo Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reportingcompany,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. If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complyingwith any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.o Indicate by check mark whether the registrant is a shell company (as defined in Rule12b-2 of the Exchange Act). YesoNoý Indicate the number of shares outstanding of each of the issuer’s classes of common stock, as of the latest practicable date. FORM10-Q FOR THE QUARTER ENDED JUNE30, 2025TABLE OF CONTENTS PARTI.FINANCIAL INFORMATION New Mountain Finance CorporationConsolidated Statements of Assets and Liabilities as ofJune30, 2025 (unaudited) and December 31,20243Consolidated Statements of Operations for the three and six months ended June 30, 2025 (unaudited) and June30, 2024 (unaudited)4Consolidated Statements of Changes in Net Assets forthe three and six months ended June 30, 2025(unaudited) and June 30, 2024 (unaudited)5Consolidated Statements of Cash Flows for the six months ended June 30, 2025 (unaudited) and June 30, 2024(unaudited)6Consolidated Schedule of Investments as ofJune 30, 2025 (unaudited)7Consolidated Schedule of Investments as of December31, 202438Notes to the Consolidated Financial Statements of New Mountain Finance Corporation (unaudited)67Report of Independent Registered Public Accounting Firm118 Item2.Management’s Discussion and Analysis of Financial Condition and Results of Operations119Item3.Quantitative and Qualitative Disclosures About Market Risk139Item4.Controls and Procedures140 PARTII.OTHER INFORMATION141 Item1.Legal Proceedings141Item1A.Risk Factors141Item2.Unregistered Sales of Equity Securities and Use of Proceeds142Item3.Defaults Upon Senior Securities142Item4.Mine Safety Disclosures143Item5.Other Information143Item6.Exhibits144Signatures145 PARTI. FINANCIAL INFORMATION New Mountain Finance CorporationConsolidated Statements of Assets and Liabilities(in thousands, except shares and per share data)(unaudited) New Mountain Finance Corporation Consolidated Statements of Operations(in thousands, except shares and per share data)(unaudited) New Mountain Finance Corporation Consolidated Statements of Changes in Net Assets(in thousands, except shares and per share data)(unaudited) New Mountain Finance CorporationConsolidated Statements of Cash Flows(in thousands)(unaudited) Consolidated Schedule of InvestmentsJune 30, 2025(in thousands, except shares)(unaudited) The accompanying notes are an integral part of these consolidated financial statements.7 New Mountain Finance Corporation Consolidated Schedule of Investments (Continued)June 30, 2025(in thousands, except shares)(unaudited) New Mountain Finance Corporation Consolidated Schedule of Investments (Continued)June 30, 2025(in thousands, except shares)(unaudited) New Mountain Finance Corporation Consolidated Schedule of Investments (Continued)June 30, 2025(in thousands, except shares)(unaudited) The accompanying notes are an integral part of these consolidated financial statements.10 New Mountain Finance Corporation Consolidated Schedule of Investments (Continued)June 30, 2025(in thousands, except shares)(unaudited) New Mountain Finance Corporation Consolidated Schedule of Investments (Continued)June 30, 2025(in thousands, except shares)(unaudited) New Mountain Finance Corporation Consolidated