Interest expense on interest-bearing deposits increased $2.9 million, or 349.8%, to $3.7 million for the three months ended March 31, 2023 from $826,000 for the three months ended March 31, 2022. The increase was due to a 165 basis point increase in the average cost of interest-bearing deposits to 2.25% for the three months ended March 31, 2023 from 0.60% for the three months ended March 31, 2022. The increase in the average cost of deposits was due to the higher interest rate environment and an increase in the average balances of certificates of deposit of $152.3 million to $503.4 million for the three months ended March 31, 2023 from $351.0 million for the three months ended March 31, 2022.
Interest expense on Federal Home Loan Bank borrowings increased $447,000, or 135.5%, from $330,000 for the three months ended March 31, 2022 to $777,000 for the three months ended March 31, 2023. The increase was due to an increase in the average cost of borrowings of 164 basis points to 3.27% for the three months ended March 31, 2023 from 1.63% for the three months ended March 31, 2022 due to the new borrowings at higher rates. The increase was also due to an increase in the average balance of borrowings of $14.3 million to $96.5 million for the three months ended March 31, 2023 from $82.3 million for the three months ended March 31, 2022.
Net interest income decreased $598,000, or 11.7%, to $4.5 million for the three months ended March 31, 2023 from $5.1 million for the three months ended March 31, 2022. The increase reflected a 80 basis point decrease in our net interest rate spread to 1.68% for the three months ended March 31, 2023 from 2.48% for the three months ended March 31, 2022. Our net interest margin decreased 59 basis points to 2.05% for the three months ended March 31, 2023 from 2.64% for the three months ended March 31, 2022.
We recorded no provision for credit losses for the three months ended March 31, 2023 or the three-month period ended March 31, 2022. As of January 1, 2023 the Bank adopted CECL and recorded a one-time adjustment of $157,000 to the allowance for credit losses. The Bank had a decrease in the loan portfolio and continues to have a low level of delinquent and non-accrual loans in the portfolio, as well as no charge-offs.
Non-interest income decreased by $61,000, or 17.8%, to $283,000 for the three months ended March 31, 2023 from $344,000 for the three months ended March 31, 2022. Gain on sale of loans decreased $74,000 as loan originations were lower in 2023 and fees and other income decreased $30,000. These decreases were partially offset by an increase in income from bank-owned life insurance of $30,000, or 19.2%, due higher balances during 2023, and an increase in fee and service charges of $13,000.
For the three months ended March 31, 2023, non-interest expense decreased $24,000, or 0.7%, over the comparable 2022 period. Salaries and employee benefits increased $99,000, or 4.8%, due to a higher employee count. Director fees decreased $55,000, or 25.8%, due to lower pension expense. The increase in advertising expense of $26,000, or 21.6%, was due to additional promotions for branch locations and new promotions on deposit and loan products. Other expense decreased $142,000, or 44.2% due to lower deferred compensation expense and other various expenses.
Income tax expense decreased $227,000, or 43.3%, to $298,000 for the three months ended March 31, 2023 from $525,000 for the three months ended March 31, 2022. The increase was due to $689,000 of lower taxable income. The effective tax rate for the three months ended March 31, 2023 and 2022 were 23.09% and 27.27%, respectively.