Net interest income after provision for loan losses increased $405,000, or 8.5%, for the nine months ended September 30, 2021 to $5.1 million as compared to $4.7 million for the nine-month period ended September 30, 2020. Total interest income increased $66,000, or 1.2%, when comparing the two periods, due to an increase in the average balance of interest-earning assets partially offset by a decrease in the yield earned on interest-earning assets. The average balance of interest-earning assets increased to $235.0 million for the nine months ended September 30, 2021 from $204.7 million for the nine months ended September 30, 2020, due primarily to increases in investment securities, partially offset by decreases in loans receivable and interest-bearing deposits with banks. The average tax equivalent yield on interest-earning assets decreased to 3.38% for the nine months ended September 30, 2021 from 3.78% for the nine months ended September 30, 2020, due primarily to a decrease in market interest rates, driven by decreases in the targeted federal funds rate in response to the COVID-19 pandemic. Total interest expense decreased $237,000, or 32.1%, when comparing the two periods due to a decrease in the average cost of interest-bearing liabilities, partially offset by an increase in the average balance of interest-bearing liabilities. The average cost of interest-bearing liabilities decreased to 0.39% for the nine months ended September 30, 2021 from 0.69% for the same period in 2020. The average balance of interest-bearing liabilities increased to $169.9 million for the nine months ended September 30, 2021 from $142.1 million for the same period in 2020, due primarily to an increase in the number and balance of savings and interest-bearing demand deposit accounts, partially offset by a decrease in time deposits. As a result of the changes in interest-earning assets and interest-bearing liabilities, the interest rate spread decreased to 2.99% from 3.09% and the net interest margin decreased to 3.09% from 3.29% for the nine-month periods ended September 30, 2021 and 2020, respectively.
Noninterest income increased $99,000, or 49.0%, for the quarter ended September 30, 2021 as compared to the same period in 2020, due primarily to increases of $42,000, $28,000, and $28,000 in deposit account service charges, brokered loan fees and ATM and debit card fee income, respectively.
Noninterest income increased $243,000, or 37.0%, for the nine months ended September 30, 2021 as compared to the same period in 2020, due primarily to increases of $164,000, $100,000, and $80,000 in brokered loan fees, ATM and debit card fee income and deposit account service charges, respectively, partially offset by a reduction of $104,000 in net gain on sales of securities available for sale. Proceeds from sales of securities available for sale were $4.5 million for the nine months ended September 30, 2020. No available for sale securities have been sold during the nine months ended September 30, 2021.
Noninterest expense increased $25,000, or 1.6%, for the quarter ended September 30, 2021 as compared to the same period in 2020. The increase was due primarily to increases in data processing fees of $23,000, compensation and benefits of $20,000, occupancy and equipment expenses of $15,000 and other expenses of $11,000, partially offset by a reduction in the impairment loss on real estate held for sale of $37,000. An impairment of $37,000 was recorded during the three months ended September 30, 2020 whereas no impairment was recorded during the three months ended September 30, 2021.
Noninterest expense increased $426,000, or 9.8%, for the nine months ended September 30, 2021 as compared to the same period in 2020. The increase was due primarily to increases in compensation and benefits of $265,000, occupancy and equipment expenses of $65,000, data processing fees of $40,000, deposit insurance premiums of $27,000, directors’ compensation expense of $19,000 and other expenses of $55,000, partially offset by decreases in professional fees of $17,000 and a reduction in the impairment loss on real estate held for sale of $37,000. An impairment of $37,000 was recorded during the nine months ended September 30, 2020 whereas no impairment was recorded during the nine months ended September 30, 2021.
The Company recorded an income tax expense of $33,000 for the quarter ended September 30, 2021, compared to an income tax benefit of $11,000 for the same period in 2020. Income tax expense for the nine months ended September 30, 2021 was $56,000 compared to $74,000 for the same period in 2020 resulting from a reduction in our effective tax rate to 4.4% for 2021 compared to 6.9% for 2020. The decrease in the effective tax rate is due largely to increased tax-exempt investment income proportionate to overall pre-tax income.
Balance Sheet Review
Total assets as of September 30, 2021 were $252.3 million compared to $235.4 million at December 31, 2020. The increase in total assets was primarily due to increases in cash and cash equivalents and investment securities of