Gross profit. Gross profit increased $9.8 million, or 10.1%, to $106.8 million for the thirteen weeks ended December 26, 2020 from $97.0 million for the thirteen weeks ended December 28, 2019. As a percentage of net sales, gross profit was 35.3% and 34.2% for the thirteen weeks ended December 26, 2020 and December 28, 2019, respectively. The increase in gross profit rate of 120 basis points was driven by a 150-basis point increase in merchandise margin rate, partially offset by 30 basis points of deleverage in buying and occupancy costs. Merchandise margin increased 150 basis points primarily as a result of better full-price selling and reduced promotions.
Selling, general and administrative expenses. SG&A expenses increased $3.1 million, or 5.0%, to $65.2 million for the thirteen weeks ended December 26, 2020 from $62.1 million for the thirteen weeks ended December 28, 2019. The increase in SG&A expenses was primarily a result of additional costs to support higher sales and expenses for both new and acquired stores. As a percentage of net sales, SG&A decreased by 30 basis points to 21.6% from 21.9% for the thirteen weeks ended December 26, 2020 and December 28, 2019, respectively. SG&A expenses as a percentage of net sales decreased by 30 basis points primarily as a result of expense leverage on higher sales.
Income from operations. Income from operations increased $6.6 million, or 19.0%, to $41.6 million for the thirteen weeks ended December 26, 2020 from $35.0 million for the thirteen weeks ended December 28, 2019. The increase in income from operations was attributable to the factors noted above. As a percentage of net sales, income from operations was 13.8% and 12.3% for the thirteen weeks ended December 26, 2020 and December 28, 2019, respectively.
Interest expense, net. Interest expense, net, was $2.3 million and $3.2 million for the thirteen weeks ended December 26, 2020 and December 28, 2019, respectively. The decrease in interest expense, net was primarily the result of a lower debt balance in the current-year period and lower interest rates associated with the debt in the current-year period.
Income tax expense. Income tax expense was $9.9 million for the thirteen weeks ended December 26, 2020, compared to $7.0 million for the thirteen weeks ended December 28, 2019. Our effective tax rate was 25.1% and 22.1% for the thirteen weeks ended December 26, 2020 and December 28, 2019, respectively. The tax rate for the thirteen weeks ended December 26, 2020 was higher than the tax rate for the thirteen weeks ended December 28, 2019, primarily due to a $0.3 million tax benefit resulting from income tax accounting for share-based compensation compared to a higher benefit of $1.1 million in the thirteen weeks ended December 28, 2019.
Net income. Net income was $29.6 million for the thirteen weeks ended December 26, 2020 compared to net income of $24.8 million for the thirteen weeks ended December 28, 2019. The increase in net income was primarily attributable to the factors noted above.
Adjusted EBITDA and Adjusted EBIT. Adjusted EBITDA increased $7.1 million, or 16.6%, to $49.9 million for the thirteen weeks ended December 26, 2020 from $42.8 million for the thirteen weeks ended December 28, 2019. Adjusted EBIT increased $6.8 million, or 18.3%, to $43.9 million for the thirteen weeks ended December 26, 2020 from $37.2 million for the thirteen weeks ended December 28, 2019. The increase in Adjusted EBITDA and Adjusted EBIT was primarily a result of the year-over-year increase in income from operations driven by an increase in gross profit and a decrease in SG&A as a percentage of net sales.
Thirty-Nine Weeks Ended December 26, 2020 Compared to Thirty-Nine Weeks Ended December 28, 2019
Net sales. Net sales decreased $22.3 million, or 3.4%, to $634.6 million for the thirty-nine weeks ended December 26, 2020 from $656.9 million for the thirty-nine weeks ended December 28, 2019. Consolidated same store sales decreased 3.2%. Excluding the impact of the 24.9% increase in e-commerce same store sales, same store sales decreased by 8.9%. The decrease in retail store sales was primarily due to decreased traffic in our stores that resulted from customers staying at home in response to the COVID-19 crisis and temporary store closures.
Gross profit. Gross profit decreased $16.0 million, or 7.3%, to $202.5 million for the thirty-nine weeks ended December 26, 2020 from $218.5 million for the thirty-nine weeks ended December 28, 2019. As a percentage of net sales, gross profit was 31.9% and 33.3% for the thirty-nine weeks ended December 26, 2020 and December 28, 2019,