Additionally, the greater scale will increase portfolio diversification as well as expand the opportunity set for additional commercial finance opportunities to include large investments and asset purchases.
Upon closing, SLR Capital Partners, the investment adviser at SLRC has voluntarily agreed to a permanent 25 basis point reduction of the annual base management fee from 1.75% to 1.5% of gross assets. The contractual step down to base management fee of 1% on gross assets above 1:1 leverage will remain in place.
The business combination is expected to be accretive to net investment income per share. Based on SLRC’s and SUNS’s balance sheet at December 31, 2021, the pro forma leverage for the combined entity would have been approximately 0.9x, translating to only a slight reduction in SLRC’s leverage.
Over time, we expect that a combination of expected cost savings, reduced base management fees, and interest savings resulting from more efficient debt financing should drive net investment income growth.
Importantly, it’s anticipated that the larger scale and capital base should allow the combined company to grow NII faster than either SLRC or SUNS would be able to achieve on a stand-alone basis and to potentially generate higher net investment income per share. At this time, I’ll turn the call over back to our CFO, Rich Peteka, to take you through the fourth quarter financial highlights.
Richard Peteka^ Thank you, Michael. SLR Investment Corp.’s net asset value at December 31, 2021, was $842.3 million or $19.93 per share compared to $853.5 million or $20.20 per share at September 30, 2021.
At December 31, 2021, SLRC’s on-balance sheet investment portfolio had a fair market value of $1.67 billion in 106 portfolio companies across 34 industries, compared to a fair market value of $1.62 billion in 106 portfolio companies across 33 industries at September 30, 2021.
At December 31, the company had $818.5 million of debt outstanding with leverage of 0.97x net debt-to-equity. When considering available capital — capacity, excuse me, from the company’s credit facilities, together with available capital from the non-recourse credit facilities at SLR Credit Solutions, SLR Equipment Finance and Kingsbridge. SLR Investment Corp. has significant available capital to fund future portfolio growth.
Moving to the P&L. For the three months ended December 31, 2021, gross investment income totaled $35.7 million versus $32.2 million for the three months ended September 30, 2021. Expenses totaled $20.8 million for the three months ended December 31, 2021, and this compared to $17.2 million for the three months ended September 30. Included in this quarter’s expenses were $0.9 million of onetime costs associated with the merger with SLR Senior Investment Corp.
Importantly, due to where SLRC is in its incentive fee catch up, these expenses were effectively incurred by the manager and not by our shareholders. Accordingly, the company’s net investment income for the three months ended December 31, 2021, totaled $14.9 million or $0.35 per average share compared to $15.0 million or $0.36 per average share for the three months ended September 30.