Main Street Investor Presentation

Middle Market Investment Portfolio MAINST CAPITAL CORPORATION Middle Market Investment Portfolio provides a diversified mix of investments and diverse sources of income to complement the LMM Investment Portfolio and a potential source of liquidity for MAIN's future investment activities 44 investments/ $410.5 million in fair value 17% of total investment portfolio at fair value Average investment size of $11.7 million(1) (less than 1% of total portfolio) Investments in secured and/or rated debt investments • 94% of Middle Market portfolio is secured debt • 92% of Middle Market debt portfolio is first lien term debt Debt yielding 7.7% (2) 95% of Middle Market debt investments bear interest at floating rates(3), providing matching with MAIN's floating rate credit facility Approximately 500 basis point net cash interest margin vs "matched" floating rate on the MAIN credit facility More investment liquidity compared to LMM (1) As of June 30, 2020; based on cost (2) Weighted-average effective yield includes amortization of deferred debt origination fees and accretion of original issue discount, but excludes fees payable upon repayment of the debt instruments and any debt investments on non-accrual status (3) 74% of floating interest rates on Middle Market debt investments are subject to contractual minimum "floor" rates Main Street Capital Corporation NYSE: MAIN mainstcapital.com Page 29

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