Financial results for the quarter ended September 30, 2021 compared to the quarter ended September 30, 2020 reflected an increase in net interest income, on a tax equivalent basis, of $1.8 million, or 12.8%, and the financial results for the nine months ended September 30, 2021 compared to the nine months ended September 30, 2020 reflected an increase of $4.4 million, or 10.8%. Measured as a percentage of average earning assets, the net interest margin (expressed on a fully taxable equivalent basis) increased to 3.78% for the quarter ended September 30, 2021 compared to 3.50% for the quarter ended September 30, 2020 and increased to 3.60% for the nine months ended September 30, 2021 compared to 3.50% for the nine months ended September 30, 2020. Net interest income and net interest margin increased primarily due to an increase in PPP fees and interest income in both the three and nine month comparative periods. The Company earned $2.1 million and $4.4 million in PPP income for the three and nine months ended September 30, 2021, respectively, compared to $0.7 million and $1.2 million for the three and nine months ended September 30, 2020, respectively.
Average interest-earning assets increased $65.8 million, or 4.1%, to $1.67 billion for the quarter ended September 30, 2021 compared to $1.60 billion for the quarter ended September 30, 2020, and average interest-bearing liabilities decreased $26.8 million, or 2.3%, to $1.13 billion for the quarter ended September 30, 2021 compared to $1.16 billion for the quarter ended September 30, 2020.
Average interest-earning assets increased $123.2 million, or 8.0%, to $1.66 billion for the nine months ended September 30, 2021 compared to $1.54 billion for the nine months ended September 30, 2020, and average interest-bearing liabilities increased $4.9 million, or 0.4%, to $1.15 billion for the nine months ended September 30, 2021 compared to $1.14 billion for the nine months ended September 30, 2020.
Total interest income (expressed on a fully taxable equivalent basis) was $17.3 million and $49.3 million for the three and nine months ended September 30, 2021, respectively, compared to $16.2 million and $48.1 million for the three and nine months ended September 30, 2020, respectively. The Company’s rates earned on interest earning assets were 4.12% and 3.97% for the three and nine months ended September 30, 2021, respectively, compared to 4.03% and 4.18% for the three and nine months ended September 30, 2020, respectively.
Interest income on loans held for investment was $15.6 million and $44.8 million for the three and nine months ended September 30, 2021, respectively, compared to $14.9 million and $44.0 million for the three and nine months ended September 30, 2020, respectively.
Average loans outstanding increased $11.5 million, or 0.9%, to $1.29 billion for the quarter ended September 30, 2021 compared to $1.27 billion for the quarter ended September 30, 2020. The average yield on loans increased to 4.81% for the quarter ended September 30, 2021 compared to 4.66% for the quarter ended September 30, 2020.
Average loans outstanding increased $48.1 million, or 3.9%, to $1.28 billion for the nine months ended September 30, 2021 compared to $1.23 billion for the nine months ended September 30, 2020. The average yield on loans decreased to 4.68% for the nine months ended September 30, 2021 compared to 4.78% for the nine months ended September 30, 2020. See the Lending and Credit Management section for further discussion of changes in the composition of the lending portfolio.
Interest income on available-for-sale securities was $1.5 million and $4.0 million for the three and nine months ended September 30, 2021, respectively, compared to $1.1 million and $3.2 million for the three and nine months ended September 30, 2020, respectively.
Average securities increased $84.4 million, or 43.2%, to $279.9 million for the quarter ended September 30, 2021 compared to $195.5 million for the quarter ended September 30, 2020. The average yield on securities was consistent at 2.15% for both quarters ended September 30, 2021 and 2020, respectively.
Average securities increased $59.1 million, or 30.7%, to $251.4 million for the nine months ended September 30, 2021 compared to $192.3 million for the nine months ended September 30, 2020. The average yield on securities decreased to 2.10% for the nine months ended September 30, 2021 compared to 2.20% for the nine months ended September 30, 2020. See the Liquidity Management section for further discussion.