The average balance of loans during the three months ended March 31, 2023, decreased by $1.1 million, or 1.4%, from the average balance for the three months ended March 31, 2022, while the average yield on loans increased 23 basis points to 3.48% for the three months ended March 31, 2023, from 3.25% for the three months ended March 31, 2022.
The average balance of investment securities increased $17.9 million, or 70.9%, to $43.3 million for the three months ended March 31, 2023, from March 31, 2022, while the average yield on investment securities increased by 186 basis points to 3.23% for the three months ended March 31, 2023, from 1.37% for the three months ended March 31, 2022. This increase in yields resulted from the effects of management’s purchasing of higher yielding securities during the quarter ended March 31, 2023.
The average balance of other interest-bearing deposits, comprised of certificates of deposit in other financial institutions, overnight deposits and stock in the Federal Home Loan Bank, decreased $5.1 million, or 18.6%, for the three months ended March 31, 2023, and the average yield increased 404 basis points to 4.33% for the three months ended March 31, 2023, from 0.29% for the three months ended March 31, 2022 reflecting the rise in the interest rate environment.
Interest Expense. Total interest expense increased $86,000, or 115.0%, to $161,000 for the three months ended March 31, 2023, compared to $75,000 for the three months ended March 31, 2022. The increase was primarily due to an increase in the average cost of deposits to 0.60% for the three months ended March 31, 2023, from 0.27% for the three months ended March 31, 2022, reflecting how management has had to increase the offered rates to be competitive as interest rates in the economy have been increasing in recent months, which was partially offset by a decrease of $2.4 million, or 2.1%, in the average balance of deposits, to $107.6 million for the three months ended March 31, 2023, compared to $110.0 million for three months ended March 31, 2022.
Net Interest Income. Net interest income increased $434,000, or 61.1%, to $1.1 million for the three months ended March 31, 2023, compared to $710,000 for the three months ended March 31, 2022. The increase reflected an increase in the interest rate spread to 2.93% for the three months ended March 31, 2023, from 2.04% for the three months ended March 31, 2022. The net interest margin increased to 3.10% for the three months ended March 31, 2023, from 2.09% for the three months ended March 31, 2022.
Provision for Loan Losses. Based on an analysis of the factors described in “Critical Accounting Policies and Use of Critical Accounting Estimates – Allowance for Loan Losses,” management concluded that a provision for loan losses was not required for each of the three months ended March 31, 2023 and 2022. The allowance for loan losses was $223,000 at both March 31, 2023 and 2022 and represented 0.28% of total loans at March 31, 2023, and 0.27% of total loans at March 31, 2022. The determination over the adequacy of the allowance for loan losses was due primarily to the low balances of nonperforming loans, delinquent loans and no net charge-offs in both periods.
Total nonperforming loans were $263,000 at March 31, 2023, compared to $231,000 at March 31, 2022. Total loans past due greater than 30 days were $1.4 million and $12 million at those respective dates. As a percentage of nonperforming loans, the allowance for loan losses was 84.8% at March 31, 2023, compared to 96.4% at March 31, 2022.
The allowance for loan losses reflects the estimate management believes to be appropriate to cover incurred probable losses which were inherent in the loan portfolio at March 31, 2023 and 2022. 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. Furthermore, as an integral part of its examination process, the OCC will periodically review our allowance for loan losses. The OCC may have judgments different than those of management, and we may determine to increase our allowance as a result of these regulatory reviews. Any material increase in the allowance for loan losses may adversely affect our financial condition and results of operations.
Non-Interest Income. Non-interest income decreased by $5,000, or 9.4%, to $49,000 for the three months ended March 31, 2023, due to normal fluctuations in the volume of fees on loans and deposits.
Noninterest Expense. Noninterest expense increased $408,000, or 58.4%, to $1.1 million for the three months ended March 31, 2023, compared to $698,000 for the three months ended March 31, 2022. The increase reflects a $143,000, or 40.0%, increase in salaries and employee benefits and an increase of $61,000, or 121.3%, in occupancy and equipment, which also included a one-time expense of $28,000 for BankOnIT installation fees. These were a direct result of adding new staff, technology, and equipment as we position ourselves for future growth. There was a $38,000, or 65.7%, increase in professional services related to increased costs of operating and the reporting requirements of a public stock company. There was a one-time expense of $122,000 for pension plan