(1)

New Mountain Finance Advisers BDC, L.L.C. (the "Investment Adviser") has agreed to bear an additional $             or $             per share, of sales load in connection with this offering, which is not reflected in the above table. All other expenses of the offering, including the sales load not being borne by the Investment Adviser, will be borne by the Operating Company. The Operating Company will incur approximately $246,580 of estimated expenses, excluding the sales load, in connection with this offering. Existing stockholders of NMFC will, and purchasers in this offering would, indirectly bear such expenses, including the sales load not being borne by the Investment Adviser, through NMFC's ownership of common membership units of the Operating Company.

(2)

To the extent that the underwriters sell more than 3,500,000 shares of NMFC's common stock, the underwriters have the option to purchase up to an additional 525,000 shares of NMFC's common stock at the public offering price, less the sales load, within 30 days of the date of this prospectus supplement. If the underwriters exercise this option in full, the total public offering price, sales load and proceeds to us will be $             , $             , and $             , respectively. If the underwriters exercise their option to purchase additional shares of NMFC's common stock, NMFC will use the proceeds from the exercise of this option to purchase additional common membership units of the Operating Company. See "Underwriting".

(3)

See "Underwriting" for details of compensation to be received by the underwriters.

PROSPECTUS SUPPLEMENT SUMMARY

          This summary highlights some of the information in this prospectus supplement and the accompanying prospectus. It is not complete and may not contain all of the information that you may want to consider. You should read carefully the more detailed information set forth under "Risk Factors" and the other information included in this prospectus supplement and the accompanying prospectus.

          In this prospectus supplement, unless the context otherwise requires, references to:

•

"NMFC" refers to New Mountain Finance Corporation, a Delaware corporation, which was incorporated on June 29, 2010;



•

"NMF SLF" refers to New Mountain Finance SPV Funding, L.L.C.;



•

"Operating Company" refers to New Mountain Finance Holdings, L.L.C., a Delaware limited liability company, which is the operating company for our business. References to the Operating Company include New Mountain Finance Holdings, L.L.C.'s wholly-owned subsidiary, NMF SLF, unless the context otherwise requires. References to the Operating Company exclude NMF SLF when referencing the Operating Company's common membership units, board of directors, and credit facility or leverage;



•

"Guardian AIV" refers to New Mountain Guardian AIV, L.P.;



•

"AIV Holdings" refers to New Mountain Finance AIV Holdings Corporation, a Delaware corporation which was incorporated on March 11, 2011, of which Guardian AIV is the sole stockholder;



•

"New Mountain Finance Entities", "we", "us" and "our" refer to NMFC, the Operating Company and AIV Holdings, collectively; except for references to the registration statement of which this prospectus forms a part and the offering of securities thereunder, in which case references to "we", "us" and "our" refer to NMFC and the Operating Company only.



•

"Investment Adviser" refers to New Mountain Finance Advisers BDC, L.L.C., the Operating Company's investment adviser;



•

"Administrator" refers to the New Mountain Finance Entities' administrator, New Mountain Finance Administration, L.L.C.;



•

"New Mountain Capital" refers to New Mountain Capital Group, L.L.C. and its affiliates;



•

"Predecessor Entities" refers to New Mountain Guardian (Leveraged), L.L.C. and New Mountain Guardian Partners, L.P., together with their respective direct and indirect wholly-owned subsidiaries prior to the initial public offering;



•

"Holdings Credit Facility" refers to the Operating Company's Amended and Restated Loan and Security Agreement with Wells Fargo Bank, National Association, dated May 19, 2011, as amended;



•

"SLF Credit Facility" refers to NMF SLF's Loan and Security Agreement with Wells Fargo Bank, National Association, dated October 27, 2010, as amended; and



•

"Credit Facilities" refers to the Holding Credit Facility and the SLF Credit Facility, collectively.

Overview

          The Operating Company is a Delaware limited liability company. The Operating Company is externally managed and has elected to be treated as a business development company ("BDC") under the Investment Company Act of 1940, as amended (the "1940 Act"). As such, the Operating Company is obligated to comply with certain regulatory requirements. The Operating Company was treated as a partnership for federal income tax purposes for so long as it had at least two members. With the completion of the underwritten secondary offering on February 3, 2014, the Operating Company's existence as a partnership for U.S. federal income tax purposes terminated and the Operating Company became an entity that is disregarded as a separate entity from its owner for U.S. federal tax purposes. See below section on Additional Material Federal Income Tax Considerations.

          The Operating Company is externally managed by the Investment Adviser. The Administrator provides the administrative services necessary for operations. The Investment Adviser and Administrator are wholly-owned subsidiaries of New Mountain Capital. New Mountain Capital is a firm with a track record of investing in the middle market and with assets under management (which includes amounts committed, not all of which have been drawn down and invested to date) totaling more than $12.0 billion as of December 31, 2013, which includes total assets held by the Operating Company. New Mountain Capital focuses on investing in defensive growth companies across its private equity, public equity, and credit investment vehicles. The Operating Company, formerly known as New Mountain Guardian (Leveraged), L.L.C., was originally formed as a subsidiary of Guardian AIV by New Mountain Capital in October 2008. Guardian AIV was formed through an allocation of approximately $300.0 million of the $5.1 billion of commitments supporting New Mountain Partners III, L.P., a private equity fund managed by New Mountain Capital. In February 2009, New Mountain Capital formed a co-investment vehicle, New Mountain Guardian Partners, L.P., comprising $20.4 million of commitments.

          NMFC is a Delaware corporation that was originally incorporated on June 29, 2010. NMFC is a closed-end, non-diversified management investment company that has elected to be treated as a BDC under the 1940 Act. As such, NMFC is obligated to comply with certain regulatory requirements. NMFC has elected to be treated, and intends to comply with the requirements to continue to qualify annually, as a regulated investment company ("RIC") under Subchapter M of the Internal Revenue Code of 1986, as amended, (the "Code").

          AIV Holdings is a Delaware corporation that was originally incorporated on March 11, 2011. Guardian AIV, a Delaware limited partnership, is AIV Holdings' sole stockholder. AIV Holdings is a closed-end, non-diversified management investment company that has elected to be treated as a BDC under the 1940 Act. As such, AIV Holdings is obligated to comply with certain regulatory requirements. AIV Holdings has elected to be treated, and intends to comply with the requirements to continue to qualify annually, as a RIC under the Code.

          On May 19, 2011, NMFC priced its initial public offering (the "IPO") of 7,272,727 shares of common stock at a public offering price of $13.75 per share. Concurrently with the closing of the IPO and at the public offering price of $13.75 per share, NMFC sold an additional 2,172,000 shares of its common stock to certain executives and employees of, and other individuals affiliated with, New Mountain Capital in a concurrent private placement (the "Concurrent Private Placement"). Additionally, 1,252,964 shares were issued to the partners of New Mountain Guardian Partners, L.P. at that time for their ownership interest in the Predecessor Entities. In connection with NMFC's IPO and through a series of transactions, the Operating Company owns all of the operations of the Predecessor Entities, including all of the assets and liabilities related to such operations.

          NMFC and AIV Holdings are holding companies with no direct operations of their own, and their sole asset is their ownership in the Operating Company. NMFC and AIV Holdings each entered

into a joinder agreement with respect to the Limited Liability Company Agreement, as amended and restated, of the Operating Company, pursuant to which NMFC and AIV Holdings were admitted as members of the Operating Company. NMFC acquired from the Operating Company, with the gross proceeds of the IPO and the Concurrent Private Placement, common membership units ("units") of the Operating Company (the number of units are equal to the number of shares of NMFC's common stock sold in the IPO and the Concurrent Private Placement). Additionally, NMFC received units of the Operating Company equal to the number of shares of common stock of NMFC issued to the partners of New Mountain Guardian Partners, L.P. Guardian AIV was the parent of the Operating Company prior to the IPO and, as a result of the transactions completed in connection with the IPO, obtained units in the Operating Company. Guardian AIV contributed its units in the Operating Company to its newly formed subsidiary, AIV Holdings, in exchange for common stock of AIV Holdings. AIV Holdings has the right to exchange all or any portion of its units in the Operating Company for shares of NMFC's common stock on a one-for-one basis at any time.

          The original structure was designed to generally prevent NMFC and its stockholders from being allocated taxable income with respect to unrecognized gains that existed at the time of the IPO in the Predecessor Entities' assets, and rather such amounts would be allocated generally to AIV Holdings and its stockholders. The result is that any distributions made to NMFC's stockholders that were attributable to such gains generally were not treated as taxable dividends but rather as return of capital. See "Material Federal Income Tax Considerations" included in the accompanying prospectus.

          Since the IPO through February 3, 2014, NMFC completed five underwritten secondary offerings of its common stock on behalf of AIV Holdings as the selling stockholder. In connection with these five secondary offerings, AIV Holdings tendered an aggregate of 20,221,938 units of the Operating Company held by AIV Holdings to NMFC in exchange for the net proceeds (after deducting underwriting discounts and commissions) of these five secondary offerings and NMFC issued an aggregate of 20,221,938 shares of its common stock directly to the underwriters for these five secondary offerings. AIV Holdings distributed all of the net proceeds from these five secondary offerings to its sole stockholder, Guardian AIV. With the completion of the final secondary offering on February 3, 2014, NMFC now owns 100.0% of the units of the Operating Company, which is now a wholly-owned subsidiary of NMFC.

          As a BDC, AIV Holdings has been subject to the 1940 Act, including certain provisions applicable only to BDCs. Accordingly, and after careful consideration of the 1940 Act requirements applicable to BDCs, the cost of 1940 Act compliance and a thorough assessment of AIV Holdings' current business model, AIV Holdings' board of directors has determined that continuation as a BDC is not in the best interests of AIV Holdings and Guardian AIV at the present time. Specifically, given that AIV Holdings was formed for the sole purpose of holding units of the Operating Company and AIV Holdings has disposed of all of the units of the Operating Company that it was holding as of February 3, 2014, the board of directors of AIV Holdings approved and declared advisable at an in-person meeting held on March 25, 2014 the withdrawal of AIV Holdings' election to be treated as a BDC under the 1940 Act. In addition, the board of directors of AIV Holdings approved and declared advisable for AIV Holdings to terminate its registration under Section 12(g) of the Exchange Act and to dissolve AIV Holdings under the laws of the State of Delaware.

          Upon receiving the necessary stockholder consent to authorize the board of directors of AIV Holdings to withdraw AIV Holdings' election to be regulated as a BDC, the withdrawal will become effective upon receipt by the Securities and Exchange Commission ("SEC") of AIV Holdings' notification of withdrawal on Form N-54C. The board of directors of AIV Holdings believes that AIV Holdings meets the requirements for filing the notification to withdraw its election to be regulated as a BDC, upon the receipt of the necessary stockholder consent. AIV Holdings anticipates filing the Form N-54C with the SEC as soon as practicable after receipt of the necessary stockholder

consent. After the application for withdrawal of AIV Holdings' BDC election is filed with the SEC, AIV Holdings will no longer be subject to the regulatory provisions of the 1940 Act applicable to BDCs generally, including regulations related to insurance, custody, composition of its board of directors, affiliated transactions and any compensation arrangements.

          After AIV Holdings files the Form N-54C with the SEC, AIV Holdings will then file a Form 15 with the SEC to terminate AIV Holdings' registration under Section 12(g) of the 1934 Act. After these SEC filings and any other federal or state regulatory or tax filings are made, AIV Holdings will proceed to dissolve under Delaware law by filing a certificate of dissolution in Delaware.

          Similarly, as a BDC, the Operating Company has been subject to the 1940 Act, including certain provisions applicable only to BDCs. Accordingly, and after careful consideration of the 1940 Act requirements applicable to BDCs, the cost of 1940 Act compliance and a thorough assessment of the Operating Company's current business model, the Operating Company's board of directors has determined that continuation as a BDC is not in the best interests of the Operating Company at the present time.

          At the 2014 joint annual meeting of the stockholders of NMFC and the sole unit holder of the Operating Company, which is expected to be held on May 6, 2014, the stockholders of NMFC and the sole unit holder of the Operating Company will be asked to vote on a proposal which would authorize the board of directors of the Operating Company to withdraw the Operating Company's election to be treated as a BDC. Additionally, the stockholders of NMFC will be asked to approve an investment advisory and management agreement between NMFC and the Investment Adviser. Upon receipt of the necessary stockholder/unit holder approval, the Operating Company's board of directors intends to withdraw the Operating Company's election to be treated as a BDC under the 1940 Act and amend its Limited Liability Company Agreement, as amended and restated (the "Operating Agreement") such that the Operating Company will remain a wholly-owned subsidiary of NMFC with the sole purpose of serving as a special purpose vehicle for the Operating Company's existing credit facilities, and NMFC will assume, with the necessary stockholder approval, all other operating activities previously undertaken by the Operating Company under the management of the Investment Adviser (the "Proposed Restructuring"). All of the current entities that will remain underneath NMFC after the Proposed Restructuring will be wholly-owned subsidiaries of NMFC and are expected to be consolidated with NMFC for both 1940 Act and financial statement reporting purposes, subject to any financial statement adjustments required in accordance with U.S. generally accepted accounting principles. In addition, the board of directors has approved and declared advisable the termination of the Operating Company's registration under Section 12(g) of the Exchange Act.

          Upon receiving the necessary stockholder approvals, the Operating Company will then amend its Operating Agreement such that the board of directors of the Operating Company will be dissolved, and the Operating Company remains a wholly-owned subsidiary of NMFC with the sole purpose of serving as a special purpose vehicle for the Operating Company's existing credit facilities. As a special purpose entity, the Operating Company will be bankruptcy-remote and non-recourse to NMFC. In addition, the assets that the Operating Company will hold will continue to be used to secure the Operating Company's current credit facilities.

          The diagram below depicts the New Mountain Finance Entities' organizational structure as of April 8, 2014.

*

Includes partners of New Mountain Guardian Partners, L.P.

          The Operating Company's investment objective is to generate current income and capital appreciation through the sourcing and origination of debt securities at all levels of the capital structure, including first and second lien debt, notes, bonds and mezzanine securities. In some cases, the Operating Company's investments may also include equity interests. The primary focus is in the debt of defensive growth companies, which are defined as generally exhibiting the following characteristics: (i) sustainable secular growth drivers, (ii) high barriers to competitive entry, (iii) high free cash flow after capital expenditure and working capital needs, (iv) high returns on assets and (v) niche market dominance.

          As of December 31, 2013, the Operating Company's net asset value was $688.5 million and its portfolio had a fair value of approximately $1,115.7 million in 59 portfolio companies, with a weighted average yield to maturity of approximately 10.6%. This yield to maturity calculation assumes that all investments not on non-accrual are purchased at fair value on December 31, 2013 and held until their respective maturities with no prepayments or losses and exited at par at

maturity. The actual yield to maturity may be higher or lower due to the future selection of the London Interbank Offered Rate ("LIBOR") contracts by the individual companies in the Operating Company's portfolio or other factors.

Additional Material Federal Income Tax Considerations

          The following discussion supplements the discussion in the prospectus under the heading "Material Federal Income Tax Considerations," which you are encouraged to review.

          As a result of the Operating Company becoming a wholly-owned subsidiary of NMFC from the completion of the underwritten secondary public offering on February 3, 2014, the Operating Company's existence as a partnership for U.S. federal income tax purposes terminated and the Operating Company became an entity that is disregarded as a separate entity from its owner for U.S. federal tax purposes. Based on preliminary analysis, NMFC does not believe that it recognized any gains or losses as a result of this transaction for tax purposes. This change in tax classification of the Operating Company from a partnership to a disregarded entity will not affect the ability of NMFC to qualify as a regulated investment company. Since the Operating Company is classified as a disregarded entity, for U.S. federal tax purposes, including for purposes of applying the 90.0% Income Test, the Diversification Tests, and the Annual Distribution Requirement, NMFC will be treated as owning all of the assets of the Operating Company and earning all of the Operating Company's income as if it holds such assets and earns such income directly. In addition, the discussion in the prospectus under the heading "Material Federal Income Tax Considerations—Investment in the Operating Company" does not apply to earnings or the assets of the Operating Company after February 3, 2014, as the Operating Company is not subject to the partnership tax provisions of the Code and not required to separately report its income for U.S. federal tax purposes after such date.

          Tax matters are very complicated and the tax consequences to an investor of an investment in our shares will depend on the facts of its particular situation. We encourage investors to consult their own tax advisors regarding the specific consequences of such an investment, including tax reporting requirements, the applicability of federal, state, local and foreign tax laws, eligibility for the benefits of any applicable tax treaty and the effect of any possible changes in the tax laws.

The Investment Adviser

          The Investment Adviser, a wholly-owned subsidiary of New Mountain Capital, manages the Operating Company's day-to-day operations and provides it with investment advisory and management services. In particular, the Investment Adviser is responsible for identifying attractive investment opportunities, conducting research and due diligence on prospective investments, structuring the Operating Company's investments and monitoring and servicing the Operating Company's investments. We currently do not have, and do not intend to have, any employees. As of December 31, 2013, the Investment Adviser was supported by approximately 100 staff members of New Mountain Capital, including 61 investment professionals.

          The Investment Adviser is managed by a five member investment committee (the "Investment Committee"), which is responsible for approving purchases and sales of the Operating Company's investments above $5.0 million in aggregate by issuer. The Investment Committee currently consists of Steven B. Klinsky, Robert A. Hamwee, Adam Collins, Douglas Londal and John Kline. In addition, the executive officers and certain investment professionals are invited to all Investment Committee meetings. The Investment Committee is responsible for approving all of the Operating Company's investment purchases above $5.0 million. The Investment Committee also approves all asset dispositions above $5.0 million. Purchases and dispositions below $5.0 million may be approved by the Operating Company's Chief Executive Officer. These approval thresholds are subject to change over time. We expect to benefit from the extensive and varied relevant experience of the investment professionals serving on the Investment Committee, which includes expertise in private equity, primary and secondary leveraged credit, private mezzanine finance and distressed debt.

Recent Developments

Green Light Letter from the U.S. Small Business Administration

          On January 27, 2014, NMFC announced that the U.S. Small Business Administration ("SBA") issued a "green light" letter inviting NMFC to continue its application process to obtain a license to form and operate a Small Business Investment Company ("SBIC") subsidiary. If approved, an SBIC license would provide NMFC with an incremental source of attractive long-term capital.

          Receipt of a green light letter from the SBA does not assure an applicant that the SBA will ultimately issue an SBIC license, and NMFC has received no assurance or indication from the SBA that it will receive an SBIC license, or of the timeframe in which it would receive a license, should one ultimately be granted.

Follow-on Offering

          On February 3, 2014, NMFC completed an underwritten secondary public offering of 2,325,000 shares of its common stock on behalf of a selling stockholder, AIV Holdings, at a public offering price of $14.70 per share. In connection with the underwritten secondary public offering, the underwriters purchased an additional 346,938 shares of NMFC's common stock from AIV Holdings with the exercise of the overallotment option to purchase up to an additional 346,938 shares of common stock. NMFC did not receive any proceeds from the sale of shares of NMFC's common stock by AIV Holdings. The Operating Company and NMFC did not bear any expenses in connection with this offering. The offering expenses were borne by the selling stockholder, AIV Holdings. As of February 3, 2014, AIV Holdings no longer owns any units of the Operating Company and NMFC owns 100.0% of the units of the Operating Company. As a result, the New Mountain Finance Entities' original organizational structure may be collapsed or simplified in the future.

Dividend

          On March 4, 2014, the Operating Company's board of directors, and subsequently NMFC's board of directors, declared a first quarter 2014 distribution of $0.34 per unit/share which was paid on March 31, 2014 to holders of record as of March 17, 2014.

Preliminary Estimates of Net Asset Value and Adjusted Net Investment Income

          Set forth below is a preliminary estimate of our net asset value per share as of April 9, 2014 and a preliminary estimate of our adjusted net investment income per share range for the three months ended March 31, 2014. The following estimates are not a comprehensive statement of our financial condition or results for the period from December 31, 2013 through March 31, 2014. We advise you that our actual results for the three months ended March 31, 2014 may differ materially from these estimates, which are given only as of the date of this prospectus supplement, as a result of the completion of our financial closing procedures, final adjustments and other developments, including changes in interest rates or changes in the businesses to whom we have made loans, which may arise between now and the time that our financial results for the three months ended March 31, 2014 are finalized. This information is inherently uncertain.

          As of the date of this prospectus supplement, we currently expect that the Operating Company's adjusted net investment income per share was between $0.35 and $0.37 for the three months ended March 31, 2014.

          As of the date of this prospectus supplement, we estimate that our net asset value per share as of April 9, 2014 is approximately $14.57.

          The preliminary financial estimates provided herein have been prepared by, and are the responsibility of, management. Neither Deloitte & Touche LLP, our independent registered public

accounting firm, nor any other independent accountants, have 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 and assumes no responsibility for, and disclaims any association with, this information.

Competitive Advantages

          We believe that we have the following competitive advantages over other capital providers to middle market companies:

Proven and Differentiated Investment Style With Areas of Deep Industry Knowledge

          In making its investment decisions, the Investment Adviser applies New Mountain Capital's long-standing, consistent investment approach that has been in place since its founding more than 10 years ago. We focus on companies in less well followed defensive growth niches of the middle market space where we believe few debt funds have built equivalent research and operational size and scale.

          We benefit directly from New Mountain Capital's private equity investment strategy that seeks to identify attractive investment sectors from the top down and then works to become a well positioned investor in these sectors. New Mountain Capital focuses on companies and industries with sustainable strengths in all economic cycles, particularly ones that are defensive in nature, that are non-cyclical and can maintain pricing power in the midst of a recessionary and/or inflationary environment. New Mountain Capital focuses on companies within sectors in which it has significant expertise (examples include federal services, software, education, niche healthcare, business services, energy and distribution and logistics) while typically avoiding investments in companies with products or services that serve markets that are highly cyclical, have the potential for long-term decline, are overly-dependent on consumer demand or are commodity-like in nature.

          In making its investment decisions, the Investment Adviser has adopted the approach of New Mountain Capital, which is based on three primary investment principles:

1.

A generalist approach, combined with proactive pursuit of the highest quality opportunities within carefully selected industries, identified via an intensive and structured ongoing research process;



2.

Emphasis on strong downside protection and strict risk controls; and



3.

Continued search for superior risk adjusted returns, combined with timely, intelligent exits and outstanding return performance.

Experienced Management Team and Established Platform

          The Investment Adviser's team members have extensive experience in the leveraged lending space. Steven B. Klinsky, New Mountain Capital's Founder, Chief Executive Officer and Managing Director and Chairman of the board of directors of the New Mountain Finance Entities, was a general partner of Forstmann Little & Co., a manager of debt and equity funds totaling multiple billions of dollars in the 1980s and 1990s. He was also a co-founder of Goldman, Sachs & Co.'s Leverage Buyout Group in the period from 1981 to 1984. Robert A. Hamwee, Chief Executive Officer and President of the New Mountain Finance Entities and Managing Director of New Mountain Capital, was formerly President of GSC Group, Inc. ("GSC"), where he was the portfolio manager of GSC's distressed debt funds and led the development of GSC's CLOs. Douglas Londal, President, Chief Operating Officer and Managing Director of New Mountain Capital, was previously co-head of Goldman, Sachs & Co.'s United States ("U.S.") mezzanine debt team. John Kline, Chief Operating Officer and Executive Vice President of the New Mountain Finance Entities and Managing Director of New Mountain Capital, worked at GSC as an investment analyst and trader for GSC's

control distressed and corporate credit funds and at Goldman, Sachs & Co. in the Credit Risk Management and Advisory Group.

          Many of the debt investments that the Operating Company has made to date have been in the same companies with which New Mountain Capital has already conducted months of intensive acquisition due diligence related to potential private equity investments. We believe that private equity underwriting due diligence is usually more robust than typical due diligence for loan underwriting. In its underwriting of debt investments, the Investment Adviser is able to utilize the research and hands-on operating experience that New Mountain Capital's private equity underwriting teams possess regarding the individual companies and industries. Business and industry due diligence is led by a team of investment professionals of the Investment Adviser that generally consists of three to seven individuals, typically based on their relevant company and/or industry specific knowledge. Additionally, the Investment Adviser is also able to utilize its relationships with operating management teams and other private equity sponsors. We believe this differentiates us from many of our competitors.

Significant Sourcing Capabilities and Relationships

          We believe the Investment Adviser's ability to source attractive investment opportunities is greatly aided by both New Mountain Capital's historical and current reviews of private equity opportunities in the business segments we target. To date, a significant majority of the investments that the Operating Company has made are in the debt of companies and industry sectors that were first identified and reviewed in connection with New Mountain Capital's private equity efforts, and the majority of our current pipeline reflects this as well. Furthermore, the Investment Adviser's investment professionals have deep and longstanding relationships in both the private equity sponsor community and the lending/agency community which they have and will continue to utilize to generate investment opportunities.

Risk Management through Various Cycles

          New Mountain Capital has emphasized tight control of risk since its inception and long before the recent global financial distress began. To date, New Mountain Capital has never experienced a bankruptcy of any of its portfolio companies in its private equity efforts or with respect to the Predecessor Entities' business. The Investment Adviser seeks to emphasize tight control of risk with our investments in several important ways, consistent with New Mountain Capital's historical approach. In particular, the Investment Adviser:

•

Emphasizes the origination or purchase of debt in what the Investment Adviser believes are defensive growth companies, which are less likely to be dependent on macro-economic cycles;



•

Targets investments in companies that are preeminent market leaders in their own industries, and when possible, investments in companies that have strong management teams whose skills are difficult for competitors to acquire or reproduce; and



•

Emphasizes capital structure seniority in the Investment Adviser's underwriting process.

Access to Non Mark to Market, Seasoned Leverage Facilities

          The amounts available under the Credit Facilities are generally not subject to reduction as a result of mark to market fluctuations in the Operating Company's portfolio investments. For a detailed discussion of the Credit Facilities, see "Management's Discussion and Analysis of Financial Conditions and Results of Operations — Liquidity and Capital Resources".

Market Opportunity

          We believe that the size of the market for investments that we target, coupled with the demands of middle market companies for flexible sources of capital at competitive terms and rates, create an attractive investment environment for us.

•

The leverage finance market has a high level of financing needs over the next several years due to significant bank debt maturities.  We believe that the large dollar volume of loans that need to be refinanced will present attractive opportunities to invest capital in a manner consistent with our stated objectives.



•

Middle market companies continue to face difficulties in accessing the capital markets.  We believe opportunities to serve the middle market will continue to exist. While many middle market companies were formerly able to raise funds by issuing high-yield bonds, we believe this approach to financing has become more difficult in recent years as institutional investors have sought to invest in larger, more liquid offerings. In addition, many private finance companies and hedge funds have reduced their middle market lending activities due to decreased availability of their own financing.



•

Consolidation among commercial banks has reduced the focus on middle market lending.  We believe that many traditional bank lenders to middle market businesses have either exited or de-emphasized their service and product offerings in the middle market. These traditional lenders have instead focused on lending and providing other services to large corporate clients. We believe this has resulted in fewer key players and the reduced availability of debt capital to the companies we target.



•

Attractive pricing.  Reduced access to, and availability of, debt capital typically increases the interest rates, or pricing, of loans for middle market lenders. Recent primary debt transactions in this market often include upfront fees, prepayment protections and, in some cases, warrants to purchase common stock, all of which should enhance the profitability of new loans to lenders.



•

Conservative deal structures.  As a result of the credit crisis, many lenders are requiring larger equity contributions from financial sponsors. Larger equity contributions create an enhanced margin of safety for lenders because leverage is a lower percentage of the implied enterprise value of the company.



•

Large pool of uninvested private equity capital available for new buyouts.  We expect that private equity firms will continue to pursue acquisitions and will seek to leverage their equity investments with mezzanine loans and/or senior loans (including traditional first and second lien, as well as unitranche loans) provided by companies such as ours.

Operating and Regulatory Structure

          NMFC and the Operating Company are closed-end, non-diversified management investment companies that have elected to be treated as BDCs under the 1940 Act and are required to maintain an asset coverage ratio, as defined in the 1940 Act, of at least 200.0%. NMFC has no material long-term liabilities itself and its only business and sole asset is its ownership of units of the Operating Company. As a result, NMFC looks to the Operating Company's assets for purposes of satisfying the requirements under the 1940 Act otherwise applicable to NMFC. See "Regulation" in the accompanying prospectus. The Operating Company and NMF SLF have long term liabilities related to the Credit Facilities.

          NMFC has elected to be treated, and intends to comply with the requirements to continue to qualify annually, as a RIC under Subchapter M of the Code. See "Material Federal Income Tax Considerations" in the accompanying prospectus. As a RIC, NMFC generally will not have to pay corporate-level federal income taxes on any net ordinary income or capital gains that it timely

distributes to its stockholders as dividends if it meets certain source-of-income, distribution and asset diversification requirements. The Operating Company intends to make distributions to its unit holders that will be sufficient to enable NMFC to pay quarterly distributions to its stockholders and to maintain its status as a RIC. NMFC intends to distribute to its stockholders substantially all of its annual taxable income, except that it may retain certain net capital gains for reinvestment in units of the Operating Company.

Risks

          An investment in NMFC's common stock involves risk, including the risk of leverage and the risk that our operating policies and strategies may change without prior notice to NMFC stockholders or prior stockholder approval. See "Risk Factors" and the other information included in this prospectus and the accompanying prospectus for a discussion of factors you should carefully consider before deciding to invest in shares of NMFC's common stock. The value of the Operating Company's assets, as well as the market price of NMFC's shares, will fluctuate. Our investments may be risky, and you may lose all or part of your investment in NMFC. Investing in NMFC involves other risks, including the following:

•

We have a limited operating history;



•

The Operating Company may suffer credit losses;



•

The Operating Company does not expect to replicate the Predecessor Entities' historical performance or the historical performance of other entities managed or supported by New Mountain Capital;



•

There is uncertainty as to the value of the Operating Company's portfolio investments because most of its investments are, and may continue to be in private companies and recorded at fair value. In addition, because NMFC is a holding company, the fair values of the Operating Company's investments are determined by the Operating Company's board of directors in accordance with the Operating Company's valuation policy;



•

The Operating Company's ability to achieve its investment objective depends on key investment personnel of the Investment Adviser. If the Investment Adviser were to lose any of its key investment personnel, the Operating Company's ability to achieve its investment objective could be significantly harmed;



•

The Investment Adviser has limited experience managing a BDC or a RIC, which could adversely affect our business;



•

The Operating Company operates in a highly competitive market for investment opportunities and may not be able to compete effectively;



•

Our business, results of operations and financial condition depends on the Operating Company's ability to manage future growth effectively;



•

The Operating Company borrows money, which could magnify the potential for gain or loss on amounts invested in us and increase the risk of investing in us;



•

Changes in interest rates may affect the Operating Company's cost of capital and net investment income;



•

Regulations governing the operations of BDCs will affect our ability to raise additional equity capital as well as our ability to issue senior securities or borrow for investment purposes, any or all of which could have a negative effect on our investment objectives and strategies;



•

We may experience fluctuations in our annual and quarterly results due to the nature of our business;

•

The Operating Company's board of directors may change its investment objective, operating policies and strategies without prior notice or member approval, the effects of which may be adverse to your interest as a stockholder;



•

NMFC will be subject to corporate-level federal income tax on all of its income if it is unable to maintain RIC status under Subchapter M of the Code, which would have a material adverse effect on its financial performance;



•

NMFC may not be able to pay you distributions on its common stock, its distributions to you may not grow over time and a portion of its distributions to you may be a return of capital for federal income tax purposes;



•

The Operating Company's investments in portfolio companies may be risky, and the Operating Company could lose all or part of any of its investments;



•

The lack of liquidity in the Operating Company's investments may adversely affect our business;



•

Economic recessions or downturns could impair the Operating Company's portfolio companies and harm its operating results;



•

NMFC is a holding company with no direct operations of its own, and will depend on distributions from the Operating Company to meet its ongoing obligations;



•

The market price of NMFC's common stock may fluctuate significantly; and



•

Sales of substantial amounts of NMFC's common stock in the public market may have an adverse effect on the market price of its common stock.

Company Information

          Our administrative and executive offices are located at 787 Seventh Avenue, 48th Floor, New York, New York 10019, and our telephone number is (212) 720-0300. We maintain a website at http://www.newmountainfinance.com. Information contained on our website is not incorporated by reference into this prospectus, and you should not consider information contained on our website to be part of this prospectus.

Presentation of Historical Financial Information and Market Data

Historical Financial Information

          Unless otherwise indicated, historical references contained in this prospectus in "Selected Financial and Other Data", "Selected Quarterly Data", "Management's Discussion and Analysis of Financial Condition and Results of Operations", "Senior Securities" and "Portfolio Companies" relate to the Operating Company, which is NMFC's sole investment. The consolidated financial statements of New Mountain Finance Holdings, L.L.C., formerly known as New Mountain Guardian (Leveraged), L.L.C., and New Mountain Guardian Partners, L.P. are the Operating Company's historical consolidated financial statements.

Market Data

          Statistical and market data used in this prospectus has been obtained from governmental and independent industry sources and publications. We have not independently verified the data obtained from these sources, and we cannot assure you of the accuracy or completeness of the data. Forward-looking information obtained from these sources is subject to the same qualifications and the additional uncertainties regarding the other forward-looking statements contained in this prospectus. See "Cautionary Statement Regarding Forward-Looking Statements".

THE OFFERING

FEES AND EXPENSES

          The following table is intended to assist you in understanding the costs and expenses that you will bear directly or indirectly. We caution you that some of the percentages indicated in the table below are estimates and may vary. Except where the context suggests otherwise, whenever this prospectus supplement and the accompanying prospectus contains a reference to fees or expenses paid by "you", "NMFC", the "Operating Company", or "us" or that "we", "NMFC", or the "Operating Company" will pay fees or expenses, stockholders will indirectly bear such fees or expenses through NMFC's investment in the Operating Company.

Example

          The following example, required by the SEC, demonstrates the projected dollar amount of total cumulative expenses that would be incurred over various periods with respect to a hypothetical investment in NMFC's common stock. In calculating the following expense amounts, we have assumed that the Operating Company's borrowings and annual operating expenses would remain at the levels set forth in the table above. See Note 6 below for additional information regarding certain assumptions regarding the Operating Company's level of leverage.

          The example and the expenses in the tables above should not be considered a representation of future expenses, and actual expenses may be greater or less than those shown.

          While the example assumes, as required by the applicable rules of the SEC, a 5.0% annual return, the Operating Company's performance will vary and may result in a return greater or less than 5.0%. The incentive fee under the Investment Management Agreement, which, assuming a 5.0% annual return, would either not be payable or would have an insignificant impact on the expense amounts shown above, is not included in the above example. The above illustration assumes that we will not realize any capital gains (computed net of all realized capital losses and unrealized capital depreciation) in any of the indicated time periods. If we achieve sufficient returns on the Operating Company's investments, including through the realization of capital gains, to trigger an incentive fee of a material amount, the Operating Company's expenses and returns to the Operating Company's investors would be higher. For example, if we assumed that we received our 5.0% annual return completely in the form of net realized capital gains on the Operating Company's investments, computed net of all cumulative unrealized depreciation on the Operating Company's

investments, the projected dollar amount of total cumulative expenses set forth in the above illustration would be as follows:

          The example assumes a sales load of 3.0%. In addition, while the examples assume reinvestment of all distributions at net asset value, participants in NMFC's dividend reinvestment plan will receive a number of shares of NMFC's common stock determined by dividing the total dollar amount of the distribution payable to a participant by the market price per share of NMFC's common stock at the close of trading on the dividend payment date. The market price per share of NMFC's common stock may be at, above or below net asset value. See "Dividend Reinvestment Plan" in the accompanying prospectus for additional information regarding the dividend reinvestment plan.

(1)

Represents the commission with respect to the shares of NMFC's common stock being sold in this offering which we will pay in connection with the sale of shares of NMFC's common stock offered by us in this offering. The Investment Adviser has agreed to bear an additional $        per share, or approximately         % of the offering price, of commission in connection with this offering, which is not reflected in the above table. There is no guaranty that there will be any sales of NMFC's common stock pursuant to this prospectus supplement and the accompanying prospectus.

(2)

The offering expenses of this offering are estimated to be approximately $246,580. Total expenses relating to the shelf registration statement that was declared effective by the SEC on December 27, 2013, of which this prospectus supplement and the accompanying prospectus form a part, are estimated to be $860,203.

(3)

The de minimus expenses of the dividend reinvestment plan are included in "other expenses".

(4)

The base management fee under the Investment Management Agreement is based on an annual rate of 1.75% of the Operating Company's average gross assets for the two most recent quarters less (i) the borrowings under the SLF Credit Facility and (ii) cash and cash equivalents. The base management fees reflected in the table above is based on the year ended December 31, 2013. See "Investment Management Agreement" in the accompanying prospectus.

(5)

Assumes that annual incentive fees earned by the Investment Adviser remain consistent with the incentive fees earned by the Investment Adviser during the year ended December 31, 2013 and includes accrued capital gains incentive fee. These accrued capital gains incentive fees would be paid by the Operating Company if the Operating Company ceased operations on December 31, 2013 and liquidated its investments at the December 31, 2013 valuation. As we cannot predict whether the Operating Company will meet the thresholds for incentive fees under the Investment Management Agreement, the incentive fees paid in subsequent periods, if any, may be substantially different than the fees incurred during the year ended December 31, 2013. For more detailed information about the incentive fee calculations, see the "Investment Management Agreement" section of the accompanying prospectus.

(6)

We may borrow funds from time to time to make investments to the extent we determine that additional capital would allow us to take advantage of additional investment opportunities or if the economic situation is otherwise conducive to doing so. The costs associated with these borrowings are indirectly borne by NMFC's stockholders through its investment in the

Operating Company. As of December 31, 2013, the Operating Company had $221.8 million and $214.7 million of indebtedness outstanding under the Holdings Credit Facility and the SLF Credit Facility, respectively. For purposes of this calculation, we have assumed the December 31, 2013 amounts outstanding under these credit facilities, and have computed interest expense using an assumed interest rate of 2.9% for the Holdings Credit Facility and 2.2% for the SLF Credit Facility, which were the rates payable as of December 31, 2013. See "Senior Securities" in this prospectus supplement.

(7)

"Other expenses" include the New Mountain Finance Entities' overhead expenses, including payments by the Operating Company under the Administration Agreement based on the allocable portion of overhead and other expenses incurred by the Administrator in performing its obligations to the New Mountain Finance Entities under the Administration Agreement. Pursuant to the Administration Agreement, and further restricted by the Operating Company, expenses payable to the Administrator by the Operating Company as well as other direct and indirect expenses (excluding interest, other credit facility expenses, trading expenses and management and incentive fees) have been capped at $3.5 million for the time period from April 1, 2012 to March 31, 2013 and capped at $4.25 million for the time period from April 1, 2013 to March 31, 2014. This expense ratio does not include any expense cap. The expense cap expired on March 31, 2014. Thereafter, the Administrator may, in its own discretion, submit to the Operating Company for reimbursement some or all of the expenses that the Administrator has incurred on behalf of the Operating Company during any quarterly period. As a result, the amount of expenses for which the Operating Company will have to reimburse the Administrator may fluctuate in future quarterly periods and there can be no assurance given as to when, or if, the Administrator may determine to limit the expenses that the Administrator submits to the Operating Company for reimbursement in the future. However, it is expected that the Administrator will continue to support part of the expense burden of the Operating Company in the near future. See "Administration Agreement" in the accompanying prospectus.

(8)

The holders of shares of NMFC's common stock indirectly bear the cost associated with our annual expenses through NMFC's investment in the Operating Company.

SELECTED FINANCIAL AND OTHER DATA

          The selected financial data should be read in conjunction with the respective financial statements and related combined notes thereto and "Management's Discussion and Analysis of Financial Condition and Results of Operations" included in this prospectus supplement and the accompanying prospectus. Financial information for the years ended December 31, 2013, December 31, 2012, December 31, 2011, December 31, 2010 and December 31, 2009 has been derived from our financial statements that were audited by Deloitte & Touche, LLP, an independent registered public accounting firm. See "Management's Discussion and Analysis of Financial Condition and Results of Operations" and "Senior Securities" in this prospectus supplement and the accompanying prospectus for more information.

          The below selected financial and other data is for the Operating Company.

(in thousands except units and per unit data)

          The below selected financial and other data is for NMFC.

(in thousands except shares and per share data)

SELECTED QUARTERLY FINANCIAL DATA

          The selected quarterly financial data should be read in conjunction with the respective financial statements and related combined notes thereto and "Management's Discussion and Analysis of Financial Condition and Results of Operations" included in this prospectus supplement and the accompanying prospectus. The following table sets forth certain quarterly financial data for each of the quarters for the fiscal years ended December 31, 2013, December 31, 2012, December 31, 2011, December 31, 2010 and December 31, 2009 of the Operating Company and for each of the quarters for the fiscal years ended December 31, 2013, December 31, 2012 and for each of the quarters from May 19, 2011 (commencement of operations) through December 31, 2011 of NMFC. This data is derived from our unaudited financial statements. Results for any quarter are not necessarily indicative of results for the full year or for any future quarter. See "Management's Discussion and Analysis of Financial Condition and Results of Operations" and "Senior Securities" included in this prospectus supplement and the accompanying prospectus for more information.

          The below selected quarterly financial data is for the Operating Company.

(in thousands except for per share data)

          The below selected quarterly financial data is for NMFC.

(in thousands except for per share data)