Interest Expense. Interest expense increased $796,000, or 35.3%, to $3.1 million for the three months ended September 30, 2019 from $2.3 million for the three months ended September 30, 2018. The increase primarily reflected a 56 basis point increase in the average cost of interest-bearing liabilities to 2.14% for the three months ended September 30, 2019 from 1.58% for the three months ended September 30, 2018, as well as a $26.2 million increase in the average balance of interest-bearing liabilities.
Interest expense on interest-bearing deposits increased $516,000, or 26.2%, to $2.5 million for the three months ended September 30, 2019 from $2.0 million for the three months ended September 30, 2018. This increase was due primarily to a 61 basis point increase in the average cost of interest-bearing deposits to 2.15% for the three months ended September 30, 2019 from 1.54% for the three months ended September 30, 2018 and a $49.3 million decrease in the average balance of deposits to $459.6 million for the three months ended September 30, 2019 from $508.9 million for the three months ended September 30, 2018. The increase in the average cost of deposits was due to the rising costs of retaining deposits in a competitive environment, a higher percentage of certificates of deposit relative to total deposits and increased competition from other financial service providers operating in our market. The decrease in the average balance of deposits was primarily due to the decrease in the average balance of certificates of deposit.
Interest expense on Federal Home Loan Bank borrowings increased $280,000, or 97.3%, from $288,000 for the three months ended September 30, 2018 to $568,000 for the three months ended September 30, 2019. The increase was primarily due to a $49.4 million increase in the average balance of Federal Home Loan Bank borrowings from $56.7 million for the three months ended September 30, 2018 to $106.1 million for the three months ended September 30, 2019. The interest expense on Federal Home Loan Bank borrowings increase was also due to a 12 basis point increase in the average cost of Federal Home Loan Bank borrowings from 2.01% for the three months ended September 30, 2018 to 2.13% for the three months ended September 30, 2019.
Net Interest Income. Net interest income decreased $505,000, or 15.5%, to $2.8 million for the three months ended September 30, 2019 from $3.3 million for the three months ended September 30, 2018. The decrease reflected a 42 basis point decrease in our net interest rate spread to 1.51% for the three months ended September 30, 2019 from 1.93% for the three months ended September 30, 2018. Our net interest margin decreased 34 basis points to 1.74% for the three months ended September 30, 2019 from 2.08% for the three months ended September 30, 2018.
Provision for Loan Losses. We did not record a provision for loan losses for either the three months ended September 30, 2019 or 2018, as a result of the low and decreasing level of delinquent andnon-accrual loans in the portfolio, as well as the absence of any charge-offs.Non-performing assets decreased to $537,000, or 0.08% of total assets, at September 30, 2019. We recorded no net charge-offs for the three months ended September 30, 2019 or 2018. The allowance for loan losses was $2.0 million, or 0.37% of net loans outstanding, at September 30, 2019.
Non-Interest Income.Non-interest income decreased $10,000, or 7.0%, to $132,000 for the three months ended September 30, 2019 from $142,000 for the three months ended September 30, 2018 due to a $12,000 decrease in bank-owned life insurance, offset by a $2,000 increase in bank fees and service charges. The decrease in bank-owned life insurance was due to changes to contractual yields.
Non-Interest Expenses.Non-interest expenses decreased $146,000, or 7.0%, to $1.9 million for the three months ended September 30, 2019 from $2.1 million for the three months ended September 30, 2018. The decrease was primarily the result of a $135,000 decrease in data processing costs. Data processing costs decreased during 2019 due to lower costs associated with credits received from our data processing conversion in February 2019.
Income Tax Expense. Income tax expense decreased $102,000, or 27.2%, to $273,000 for the three months ended September 30, 2019 from $375,000 for the three months ended September 30, 2018. The decrease was due primarily to a $369,000 decrease inpre-tax income. The effective tax rate for 2019 and 2018 was 28.9%.
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