Total loans greater than 30 days past due were $6.6 million at March 31, 2021, $47.8 million at December 31, 2020, and $9.5 million at March 31, 2020.
Traditional Special Mention (Watch) loans were $135.2 million at March 31, 2021, compared to $152.9 million at December 31, 2020 and $48.3 million at March 31, 2020. The increase compared to March 31, 2020 reflected certain multi-family projects that have experienced cost over-runs funded by the borrower and lower than projected rent collections and occupancy levels, all of which have contributed to lower than projected cash flow of the projects. An additional category of Special Mention (Watch) loans was added as of June 30, 2020, and as of March 31, 2021 included $390,000 in arrangements related to COVID-19 deferral plans that were not already included in the traditional Special Mention or Substandard categories. Classified (substandard, doubtful and loss) loans were $9.0 million at March 31, 2021, $14.5 million at December 31, 2020 and $14.1 million at March 31, 2020.
During the three months ended March 31, 2021 there were $74,000 of charge-offs and $2,000 of recoveries, compared to $1,000 of charge-offs and $44,000 of recoveries for the three months ended March 31, 2020.
Comparison of Operating Results for the Three Months Ended March 31, 2021 and 2020
General. Net income for the three months ended March 31, 2021 was $62.0 million, an increase of $37.4 million, or 152%, from net income of $24.6 million for the three months ended March 31, 2020. The increase was due to a $33.6 million, or 88%, increase in net interest income that reflected significant growth in multi-family and mortgage warehouse loans, a $13.8 million increase in loan servicing fees that were primarily associated with a positive fair market value adjustment to mortgage servicing rights, and a $7.5 million, or 35%, increase in gain on sale of loans.
Partially offsetting the increases to net income was a $13.8 million increase in the provision for income taxes due to a 155% increase in pre-tax income, as well as a $7.0 million, or 49%, increase in salaries and employee benefits to support higher loan production volumes.
Net Interest Income. Net interest income increased $33.6 million, or 88%, to $72.0 million for the three months ended March 31, 2021, compared with the three months ended March 31, 2020. The increase was due to significantly higher loan growth and higher net interest margin. The interest rate spread of 2.93% for the three months ended March 31, 2021 increased 74 basis points compared to 2.19% for the three months ended March 31, 2020.
Our net interest margin increased 59 basis points, to 2.99%, for the three months ended March 31, 2021 from 2.40% for the three months ended March 31, 2020. The increase in net interest margin reflected higher loan volume and lower funding costs that outpaced the lower interest rates on loans.
Interest Income. Interest income increased $19.1 million, or 32%, to $79.5 million for the three months ended March 31, 2021, compared with the three months ended March 31, 2020. This increase was primarily attributable to significant loan growth that was partially offset by lower rates.
The average balance of loans, including loans held for sale, during the three months ended March 31, 2021 increased $3.4 billion, or 67%, to $8.4 billion compared to the three months ended March 31, 2020, while the average yield on loans decreased 64 basis points, to 3.66%, for the three months ended March 31, 2021, compared to 4.30% for the three months ended March 31, 2020. The increase in average balances of loans and loans held for sale was primarily due to significant increases in multi-family volume. The decrease in the average yield on loans reflected higher loan volume and lower overall interest rates in the economy period to period.
The average balance of mortgage loans in process of securitization increased $150.5 million, or 43%, to $500.2 million for the three months ended March 31, 2021, compared to $349.7 million for the three months ended March 31, 2020, while the average yield decreased 68 basis points to 2.54% for the three months ended March 31, 2021.