The average balance of investment securities decreased $837,000 to $11.8 million for the three months ended December 31, 2024, from $12.6 million for the three months ended December 31, 2023, while the average yield on investment securities increased by 80 basis points to 2.93% for the three months ended December 31, 2024, from 2.13% for the three months ended December 31, 2023.
Interest income on other interest-bearing deposits, comprised primarily of certificates of deposit in other financial institutions, overnight deposits and stock in the Federal Home Loan Bank, decreased $18,000, or 18.3%, for the three months ended December 31, 2024, due primarily to a decrease in the average balance of $2.8 million, while the average yield increased by 116 basis points to 5.85% for the three months ended December 31, 2024, from 4.69% for the three months ended December 31, 2023.
Interest Expense. Total interest expense increased $244,000, or 49.3%, to $740,000 for the three months ended December 31, 2024, from $496,000 for the three months ended December 31, 2023. Interest expense on deposits increased $133,000, or 40.5%, due primarily to an increase of 38 basis points in the average cost of deposits to 1.56% for the three months ended December 31, 2024, from 1.18% for the three months ended December 31, 2023, and an increase of $6.9 million, or 6.2%, in the average balance of interest-bearing deposits to $118.4 million for the three months ended December 31, 2024, from $111.5 million for the three months ended December 31, 2023.
Interest expense on borrowings increased $111,000, or 66.9%, for the three months ended December 31, 2024, compared to the three months ended December 31, 2023. The increase was due to a $9.5 million increase in the average balance outstanding, to $22.5 million for the three months ended December 31, 2024, from $13.0 million for the three months ended December 31, 2023, partially offset by a 19 basis point decrease in the weighted-average rate, to 4.92% for the three months ended December 31, 2024, from 5.11% for the three months ended December 31, 2023.
Net Interest Income. Net interest income increased $212,000, or 15.3%, to $1.6 million for the three months ended December 31, 2024, compared to $1.4 million for the three months ended December 31, 2023. The increase reflected an increase in the net interest margin to 4.01% for the three months ended December 31, 2024, from 3.74% for the three months ended December 31, 2023. The net interest margin was impacted by a series of interest rate increases in the economy in the past several years, although recently there have been three decreases in rates, totaling 100 basis points, by the Federal Reserve Board.
Provision for Credit Losses. Based on an analysis of the loan portfolio and asset quality, management determined that no provision for credit losses was required for the three-month period ended December 31, 2024. The Company adopted the new standard effective October 1, 2023, which resulted in a $32,000 increase to the allowance for credit losses and a charge, net of tax, of $25,280 to retained earnings for the three months ending December 31, 2023. The allowance for credit losses was $960,000 at December 31, 2024 and $963,000 at September 30, 2024 and represented 0.64% and 0.65% of total loans at December 31, 2024 and September 30, 2024, respectively. The determination over the adequacy of the allowance for credit losses included consideration of the low balances of nonperforming loans and delinquent loans in both periods.
Total nonperforming loans were $697,000 at December 31, 2024, compared to $386,000 at September 30, 2024. Classified loans totaled $674,000 at December 31, 2024, compared to $482,000 at September 30, 2024, and total loans past due greater than 30 days were $1.7 million and $1.3 million at those respective dates. As a percentage of nonperforming loans, the allowance for credit losses was 137.8% at December 31, 2024 compared to 249.6% at September 30, 2024.
The allowance for credit losses reflects the estimate management believes to be appropriate to cover incurred probable losses which were inherent in the loan portfolio at December 31, 2024 and 2023. While management believes the estimates and assumptions used in the determination of the adequacy of the allowance are reasonable, such estimates and assumptions could be proven incorrect in the future, and the actual amount of future provisions may exceed the amount of past provisions, and the increase in future provisions that may be required may adversely impact the Bank’s financial condition and results of operations. In addition, bank regulatory agencies periodically review the allowance for