Interest expense on borrowings increased $294,000 to $1.7 million for the second quarter of 2020, compared to $1.4 million for the second quarter of 2019. This increase was primarily due to increased average balances of FHLB advances and subordinated debentures, partially offset by decreases in average rate paid on borrowings.
Six Months Ended June 30, 2020 Compared to Six Months Ended June 30, 2019
Net interest income was $41.4 million for the six months ended June 30, 2020, an increase of $6.2 million, or 17.5%, compared to $35.3 million for the six months ended June 30, 2019. The increase in net interest income was primarily attributable to growth in average interest earning assets due to organic growth in the loan portfolio. The Company anticipates that its interest income will be adversely affected in future periods as a result of the COVID-19 pandemic and the effects of lower interest rates.
Net interest margin (on a fully tax-equivalent basis) for the six months ended June 30, 2020 was 3.48%, compared to 3.57% for the six months ended June 30, 2019, a decrease of 9 basis points. Despite a significant reduction in interest bearing liability costs over the year, the historically low interest rate environment, coupled with a more liquid balance sheet mix, pressured earning asset yields lower and ultimately compressed the net interest margin year-over-year.
Average interest earning assets for the six months ended June 30, 2020 increased $403.2 million, or 20.0%, to $2.42 billion from $2.02 billion for the six months ended June 30, 2019. This increase in average interest earning assets was due to continued organic growth in the loan portfolio. Average interest bearing liabilities increased $257.6 million, or 18.2%, to $1.67 billion for the six months ended June 30, 2020, from $1.42 billion for the six months ended June 30, 2019. The increase in average interest bearing liabilities was primarily due to an increase in interest bearing deposits and FHLB advances, offset partially by a decrease in brokered deposits, federal funds purchased and notes payable.
Average interest earning assets produced a tax-equivalent yield of 4.66% for the six months ended June 30, 2020, compared to 5.02% for the six months ended June 30, 2019. The average rate paid on interest bearing liabilities was 1.70% for the six months ended June 30, 2020, compared to 2.07% for the six months ended June 30, 2019.
Interest Income. Total interest income on a tax-equivalent basis was $56.1 million for the six months ended June 30, 2020, compared to $50.3 million for the six months ended June 30, 2019. The $5.9 million, or 11.7%, increase in total interest income on a tax-equivalent basis was primarily due to organic growth in the loan portfolio.
Interest income on the investment securities portfolio on a fully-tax equivalent basis increased $405,000, or 9.4%, during the six months ended June 30, 2020 compared to the six months ended June 30, 2019, due to a $42.7 million, or 17.3%, increase in average balances between the periods, which was offset partially by a 24 basis point decrease in the aggregate portfolio yield.
Interest income on loans for the six months ended June 30, 2020 was $51.1 million, compared to $45.5 million for the six months ended June 30, 2019. The $5.6 million, or 12.3%, increase was primarily due to a 18.6% increase in the average balance of loans outstanding, which was offset partially by a 30 basis point decrease in the average yield on loans. The increase in the average balance of loans outstanding was due to organic loan growth. The decrease in yield on the loan portfolio was primarily driven by lower market interest rates.
Interest Expense. Interest expense on interest bearing liabilities decreased $328,000, or 2.3%, to $14.2 million for the six months ended June 30, 2020, compared to $14.5 million for the six months ended June 30, 2019, due to lower interest rates paid on both deposits and borrowings.
Interest expense on deposits decreased to $10.9 million for the six months ended June 30, 2020, compared to $11.7 million for the six months ended June 30, 2019. The $829,000, or 7.1%, decrease in interest expense on deposits was primarily due to a 39 basis point decrease in the average rate paid, even as the average balance of deposits increased 16.3%. The decrease in the average rate paid was primarily due to the impact of lower market interest rates. The increase in the average balance of interest bearing deposits resulted primarily from increases in interest bearing transaction deposits and savings and money market deposits.