General and Administrative Expenses
General and administrative expenses include compensation and benefits; professional fees such as portfolio servicing, legal, accounting and rating agency fees; and general office expenses such as insurance, office rent and travel costs. General and administrative costs totaled $15.9 million and $33.0 million for the three and six months ended June 30, 2022, respectively, as compared to $16.1 million and $41.1 million, respectively, for the same periods in 2021.
General and administrative expenses for the first six months of 2021 included $10.1 million related to the expense for certain modified performance-based stock based compensation awards granted in 2018 and 2019; excluding this one-time expense catch-up from 2021 expenses, general and administrative expenses increased $2.0 million for the first six months of 2022 as compared to 2021.
We expect that general and administrative expenses will continue to rise in some measure as our real estate investment portfolio grows. Certain expenses, such as property related insurance costs and the costs of servicing the properties and loans comprising our real estate portfolio, increase in direct proportion to the increase in the size of the portfolio. However, general and administrative expenses as a percentage of the portfolio have decreased over time due to efficiencies and economies of scale. Excluding noncash, stock-based compensation expense from both periods, general and administrative expenses for the twelve-month period ended June 30, 2022 represented 0.44% of average portfolio assets as compared to 0.46% for the comparable twelve-month period ended June 30, 2021.
Depreciation and Amortization Expense
Depreciation and amortization expense, which increases in proportion to the increase in the size of our real estate portfolio, rose from $65.0 million and $128.6 million for the three and six months ended June 30, 2021, respectively, to $76.0 million and $148.7 million, respectively, for the comparable periods in 2022.
Provisions for Impairment
During the three and six months ended June 30, 2022, we recognized $5.3 million and $6.5 million, respectively, in provisions for the impairment of real estate, and during the six months ended June 30, 2022, recognized a net reduction of $0.3 million in provisions for credit losses related to our loans and financing receivables. We recognized an aggregate $6.6 million and $14.0 million in provisions for the impairment of real estate and credit losses during the three and six months ended June 30, 2021, respectively.
Net Gain on Dispositions of Real Estate
As part of our ongoing active portfolio management process, we sell properties from time to time in order to enhance the diversity and quality of our real estate portfolio and to take advantage of opportunities to recycle capital. During the three months ended June 30, 2022, we recognized a $13.7 million aggregate net gain on the sale of 13 properties. In comparison, for the three months ended June 30, 2021, we recognized a $5.9 million aggregate net gain on the sale of 13 properties. For the six months ended June 30, 2022, we recognized a $19.7 million aggregate net gain on sale of 24 properties as compared to an aggregate net gain of $21.5 million on the sale of 57 properties for the same period in 2021.
Net Income
For the three and six months ended June 30, 2022, our net income was $90.5 million and $177.5 million, respectively, reflecting increases from $62.4 million and $117.4 million, respectively, for the comparable periods in 2021. The change in net income is primarily comprised of a net increase resulting from the growth in our real estate investment portfolio, which generated additional rental revenues and interest income, and lower general and administrative expenses, property costs and impairments which were primarily offset by increases in depreciation and amortization and interest expense, as noted above.