Interest and credit facility related expenses were $4.9 million and $9.7 million, respectively, for the three and six months ended June 30, 2013, compared to $5.0 and $9.7 million for the three and six months ended June 30, 2012. The comparable amounts reflect average debt outstanding of $313.9 million for the 2013 period at a weighted average cost of debt of 5.80%, as compared to average debt outstanding of $375.6 million for the 2012 period with a weighted average cost of debt of 4.96%.
Professional fees were $1.1 million and $0.5 million, respectively, for the six month periods ended June 30, 2013 and 2012. The spike in professional fees during the current period is due to a one-time legal fee accrual in connection with a portfolio company.
Removing the incentive management fee accrual based on capital gains, total expenses for the six months ended June 30, 2013 and 2012 were relatively consistent at $27.7 million and $27.3 million, respectively. Expenses also consist of investment advisor expenses, amortization of debt issuance costs, administrative services expense, director fees and miscellaneous other expenses.
Net Investment IncomeContinuing our positive earnings momentum, net investment income totaled $21.2 million and $34.2 million, or $0.29 per share and $0.46 per share, respectively, for the three and six months ended June 30, 2013. Included in these amounts are $2.1 million and $7.3 million of aggregate incentive management fees, as required to be accrued under GAAP. Excluding such fees, and including $4.2 million and $6.3 million, respectively, of income based incentive management fees, had they been accrued ratably throughout the year, our net investment income, as adjusted, would have been $19.1 million, or $0.26 per share, and $35.2 million, or $0.48 per share. On a trailing four quarters basis, we continued to cover dividends paid out of our $1.04 per share of adjusted net investment income. Our portfolio continues to produce a stable amount of interest and dividend income relative to its size. Alternate presentations of net investment income per share reflecting adjustments to certain GAAP requirements can be found in the Supplemental table on page 8.