53.7% for the comparable 2020 period. Our GAAP loss ratio excluding loss adjustment expenses for the three months ended September 30, 2021 was 52.1% compared to 38.5% for the comparable 2020 period. Our GAAP loss ratio excluding loss adjustment expenses for the nine months ended September 30, 2021 was 48.3% compared to 43.9% for the comparable 2020 period. Total prior year favorable development included in the pre-tax results for the three months ended September 30, 2021 was $15,403 compared to $15,291 for the comparable 2020 period. Total prior year favorable development included in the pre-tax results for the nine months ended September 30, 2021 was $41,211 compared to $34,619 for the comparable 2020 period.
Underwriting, Operating and Related Expenses. Underwriting, operating and related expenses for the three months ended September 30, 2021 decreased by $5,305, or 7.7%, to $63,291 from $68,596 for the comparable 2020 period. Underwriting, operating and related expenses for the nine months ended September 30, 2021 decreased by $1,788, or 0.9%, to $193,404 from $195,192 for the comparable 2020 period. The decreases in both periods are driven by a decrease in contingent commission expense. Our GAAP expense ratio for the three months ended September 30, 2021 decreased to 32.6% from 35.2% for the comparable 2020 period. Our GAAP expense ratio for the nine months ended September 30, 2021 decreased to 33.3% from 34.0% for the comparable 2020 period.
Interest Expense. Interest expense was $131 for the three months ended September 30, 2021 and 2020, respectively. Interest expense was $390 for the nine months ended September 30, 2021 compared to $308 for the comparable 2020 period. The credit facility commitment fee included in interest expense was $56 for the nine months ended September 30, 2021 and 2020.
Income Tax Expense. Our effective tax rate was 20.3% and 21.0% for the three months ended September 30, 2021 and 2020, respectively. Our effective tax rate was 20.4% and 20.3% for the nine months ended September 30, 2021 and 2020. The effective tax rates for the three and nine months ended September 30, 2021 and 2020 were lower than the statutory rate primarily due to the effects of tax-exempt investment income and the impact of stock-based compensation.
Net Income. Net income for the three months ended September 30, 2021 was $24,820 compared to net income of $44,742 for the comparable 2020 period. Net income for the nine months ended September 30, 2021 was $98,661 compared to net income of $85,246 for the comparable 2020 period.
Non-GAAP Operating Income. Non-GAAP operating income, as defined above, was $25,823 for the three months ended September 30, 2021 compared to $38,128 for the comparable 2020 period. Non-GAAP operating income was $82,667 for the nine months ended September 30, 2021 compared to $92,049 for the comparable 2020 period.
Liquidity and Capital Resources
As discussed in the Regulatory Matters section below, as a holding company, Safety’s assets consist primarily of the stock of our direct and indirect subsidiaries. Our principal source of funds to meet our obligations and pay dividends to shareholders, therefore, is dividends and other permitted payments from our subsidiaries, principally Safety Insurance. Safety is the borrower under our credit facility.
Safety Insurance’s sources of funds primarily include premiums received, investment income, and proceeds from sales and redemptions of investments. Safety Insurance’s principal uses of cash are the payment of claims, operating expenses and taxes, the purchase of investments, and the payment of dividends to Safety.
Net cash provided by operating activities was $110,584 and $76,112 during the nine months ended September 30, 2021 and 2020, respectively. Our operations typically generate positive cash flows from operations as most premiums are received in advance of the time when claim and benefit payments are required. Positive operating cash flows are expected in the future to meet our liquidity requirements.
Net cash used for investing activities was $79,005 and $9,497 during the nine months ended September 30, 2021 and 2020, respectively. Fixed maturities, equity securities, and other invested assets purchased were $336,374 for