For the periods shown in the tables immediately above, the provision related to increases or decreases in specific allowances on impaired loans was affected by changes in the results of management’s assessment of the amount of probable or actual (charged-off) losses associated with a small number of larger, individual loans. This line item also includes net charge-offs or recoveries from smaller loans that had not been individually evaluated for impairment prior to charge-off.
In the tables immediately above, the portion of the net change in the collectively determined allowance attributable to loan growth was determined by applying the historical loss experience and qualitative factors used in the allowance calculation at the end of the preceding period to the net increase or reduction in loans outstanding (excluding purchased loans and loans specifically evaluated for impairment) for the period.
The effect on the provision of changes in historical loss experience and qualitative factors, as shown in the tables above, was determined by: (1) calculating the net change in each factor used in determining the allowance at the end of the period as compared to the preceding period, and (2) applying the net change in each factor to the outstanding balance of loans at the end of the preceding period (excluding loans specifically evaluated for impairment).
The provision for loan losses in the third quarter 2021 and 2020, and in the nine-month periods ended September 30, 2021 and 2020, included the impact of a large charge-off in the third quarter of each year.
In the third quarter 2021, the Corporation recorded a partial charge-off of $1,194,000 on a commercial loan with an outstanding balance of $3,496,000 at the time of the charge-off. There was a specific allowance for loan losses of $583,000 on this commercial loan at June 30, 2021, with no specific allowance at December 31, 2020. At September 30, 2021, there was no specific allowance on the loan, and the Corporation’s recorded investment in the loan of $2,302,000 is reported as non-accrual and impaired.
In the third quarter 2020, the Corporation recorded a charge-off of $2,219,000 on a commercial loan for which an allowance of $1,193,000 had been recorded at June 30, 2020 but for which there was no specific allowance at December 31, 2019. The Corporation had no recorded investment in this loan at September 30, 2021 and December 31, 2020.
In the three months ended September 30, 2021, net charge-offs were $1,205,000, including recoveries of $15,000 and charge-offs of $1,220,000. For the nine months ended September 30, 2021, net charge-offs were $1,218,000 including recoveries of $60,000 and charge-offs of $1,278,000. Table VIII shows the average rate of net charge-offs as a percentage of loans was 0.08% in the nine months ended September 30, 2021, and annual average rates ranging from a high of 0.16% in 2020 to a low of 0.02% in 2018.
Table X presents information related to past due and impaired loans, and loans that have been modified under terms that are considered TDRs. Total nonperforming loans as a percentage of outstanding loans was 1.48% at September 30, 2021, up from 1.42% at December 31, 2020, and nonperforming assets as a percentage of total assets was 1.05% at September 30, 2021, down from 1.10% at December 31, 2020. Table X presents data at the end of each of the years ended December 31, 2016 through 2020. Table X shows that total nonperforming loans as a percentage of loans of 1.48% at September 30, 2021, though up from December 31, 2020 and 2019, was lower than the corresponding year-end ratio from 2016 through 2018. Similarly, the September 30, 2021 ratio of total nonperforming assets as a percentage of assets of 1.05% was lower than the corresponding ratio from 2016 through 2018.
Total impaired loans of $18,014,000 at September 30, 2021 are up $196,000 from the corresponding amount at December 31, 2020 of $17,818,000. Purchased credit impaired loans, primarily acquired from Covenant, were included in impaired loans and had carrying values totaling $6,624,000 at September 30, 2021 and $6,841,000 at December 31, 2020. Table X shows that the total balance of impaired loans at September 30, 2021 was higher than the year-end amounts over the period 2016-2020, which ranged from a low of $5,486,000 in 2019 to the high of $17,818,000 at December 31, 2020. Similarly, total nonperforming assets of $24,639,000 at September 30, 2021 and $24,729,000 at December 31, 2020 were up from the prior periods including the impact of purchased credit impaired loans from the Covenant acquisition.
As reflected in Table X, total loans past due 30-89 days and still accruing interest amounted to $2,139,000 at September 30, 2021, down from $5,918,000 at December 31, 2020. This variance includes the effect of fluctuations in 30-89 day past due residential mortgage loans, which totaled $1,775,000 at September 30, 2021, down from $5,084,000 at December 31, 2020. Management monitors the status