balances held by municipal customers as well as increases in deposits related to PPP and other government stimulus programs.
Interest expense on total borrowed funds increased $143,000 in 2020 as compared to 2019. The average balance of total borrowed funds increased to $164,057,000 in the third quarter 2020 from $81,774,000 in the third quarter 2019, while the average rate on borrowed funds decreased to 1.65% in the third quarter 2020 from 2.62% in the third quarter 2019. The increase in borrowed funds includes the impact of borrowings assumed from Covenant which were recorded at fair values totaling $74,066,000 on July 1, 2020.
Interest expense on short-term borrowings decreased $73,000 to $73,000 in 2020 from $146,000 in 2019. The average balance of short-term borrowings increased to $44,660,000 in 2020 from $25,823,000 in 2019. The average rate on short-term borrowings decreased to 0.65% in 2020 from 2.24% in 2019, reflecting the impact of lower short-term market rates in 2020.
Interest expense on long-term borrowings (FHLB advances) increased $85,000 to $362,000 in 2020 from $277,000 in 2019. The average balance of long-term borrowings was $102,857,000 in 2020, up from an average balance of $48,953,000 in 2019. Borrowings are classified as long-term within the Tables based on their term at origination or assumption in business combinations. The average rate on long-term borrowings was 1.40% in 2020 compared to 2.24% in the third quarter of 2019.
Interest expense on subordinated debt increased $131,000 to $247,000 in 2020 from $116,000 in 2019. The average balance of subordinated debt increased to $16,540,000 in 2020 from $6,998,000 in 2019 as a result of subordinated debt agreements assumed in the Covenant transaction. The average rate incurred on subordinated debt was 5.94% in 2020, down from 6.58% in 2019.
Nine-Month Periods Ended September 30, 2020 and 2019
For the nine-month periods, fully taxable equivalent net interest income was $48,524,000 in 2020, $7,515,000 (18.3%) higher than in 2019. Interest income was $7,722,000 higher in 2020 as compared to 2019, while interest expense was higher by $207,000 in comparing the same periods. As presented in Table III, the Net Interest Margin was 3.67% in 2020 as compared to 3.90% in 2019, and the “Interest Rate Spread” (excess of average rate of return on earning assets over average cost of funds on interest-bearing liabilities) was 3.44% in 2020, down from 3.61% in 2019. The overall increase in net interest income, despite margin compression, resulted mainly from growth attributable to the acquisitions of Monument in the second quarter 2019 and Covenant in the third quarter 2020.
Accretion and amortization of purchase accounting adjustments related to the Covenant and Monument acquisitions had a positive effect on net interest income in the nine months ended September 30, 2020 of $1,999,000, including an increase in income on loans of $1,288,000 and net reductions in interest expense on time deposits and borrowed funds totaling $711,000. The net positive impact to the net interest margin from purchase accounting adjustments was 0.15% in the first nine months of 2020 and $408,000, or 0.04% in 2019.
INTEREST INCOME AND EARNING ASSETS
Interest income totaled $56,015,000 in 2020, an increase of $7,722,000 (16.0%) from 2019. Interest and fees on loans receivable increased $8,988,000, or 22.2%, to $49,438,000 in 2020 from $40,450,000 in 2019. Table IV shows the increase in interest on loans includes an increase of $11,816,000 attributable to changes in volume and a decrease of $2,828,000 related to changes in average rates.
For the first nine months of 2020, average outstanding loans totaled $1.370 billion, an increase of $348.8 million (34.2%) over the comparative amount for the first nine months of 2019. The nine-month average amount of loans outstanding attributable to the former Covenant operations totaled $158.7 million, of which the nine-month average balance of PPP loans was $21.6 million. Excluding Covenant, the Corporation’s average loans outstanding increased