Thirteen Weeks Ended December 28, 2019 Compared to Thirteen Weeks Ended December 29, 2018
Net sales. Net sales increased $30.0 million, or 11.8%, to $284.0 million for the thirteen weeks ended December 28, 2019 from $254.0 million for the thirteen weeks ended December 29, 2018. Consolidated same store sales increased 6.7%. Excluding the impact of the 11.0% increase in e-commerce same store sales, same store sales increased by 5.7%. Net sales increased during the thirteen weeks ended December 28, 2019 due to the increase in same store sales and sales from stores added over the past twelve months.
Gross profit. Gross profit increased $11.4 million, or 13.3%, to $97.0 million for the thirteen weeks ended December 28, 2019 from $85.7 million for the thirteen weeks ended December 29, 2018. As a percentage of net sales, gross profit was 34.2% and 33.7% for the thirteen weeks ended December 28, 2019 and December 29, 2018, respectively. Gross profit increased primarily due to increased sales and an increase in merchandise margin rate. As a percentage of net sales, consolidated gross profit primarily increased as a result of a 50 basis point increase in merchandise margin rate. The higher merchandise margin was driven by growth in exclusive brand penetration.
Selling, general and administrative expenses. SG&A expenses increased $5.7 million, or 10.1%, to $62.1 million for the thirteen weeks ended December 28, 2019 from $56.4 million for the thirteen weeks ended December 29, 2018. As a percentage of net sales, SG&A was 21.9% and 22.2% for the thirteen weeks ended December 28, 2019 and December 29, 2018, respectively. 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 primarily as a result of expense leverage on higher sales.
Income from operations. Income from operations increased $5.7 million, or 19.4%, to $35.0 million for the thirteen weeks ended December 28, 2019 from $29.3 million for the thirteen weeks ended December 29, 2018. As a percentage of net sales, income from operations was 12.3% and 11.5% for the thirteen weeks ended December 28, 2019 and December 29, 2018, respectively. The increase in income from operations was attributable to the factors noted above.
Interest expense, net. Interest expense, net, was $3.2 million and $4.0 million for the thirteen weeks ended December 28, 2019 and December 29, 2018, respectively. The decrease in interest expense, net was primarily the result of a lower 2015 Golub Term Loan balance in the current-year period relative to the prior-year period, partially offset by a higher outstanding balance on the June 2015 Wells Fargo Revolver in the current-year period.
Income tax expense. Income tax expense was $7.0 million and $6.3 million for the thirteen weeks ended December 28, 2019 and December 29, 2018, respectively. Our effective tax rate was 22.1% and 24.8% for the thirteen weeks ended December 28, 2019 and December 29, 2018, respectively. The effective tax rate for the thirteen weeks ended December 28, 2019 is lower than the comparable period in the prior year due primarily to a $1.1 million tax benefit due to income tax accounting for share-based compensation compared to a lower tax benefit of less than $0.1 million for the thirteen weeks ended December 29, 2018.
Net income. Net income increased $5.8 million to $24.8 million for the thirteen weeks ended December 28, 2019, from $19.0 million for the thirteen weeks ended December 29, 2018. The increase in net income was primarily attributable to the factors noted above.
Adjusted EBITDA and Adjusted EBIT. Adjusted EBITDA increased $7.4 million, or 20.7%, to $42.8 million for the thirteen weeks ended December 28, 2019 from $35.5 million for the thirteen weeks ended December 29, 2018. Adjusted EBIT increased $6.4 million, or 20.8%, to $37.2 million for the thirteen weeks ended December 28, 2019 from $30.8 million for the thirteen weeks ended December 29, 2018. 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 28, 2019 Compared to Thirty-Nine Weeks Ended December 29, 2018
Net sales. Net sales increased $72.8 million, or 12.5%, to $656.9 million for the thirty-nine weeks ended December 28, 2019 from $584.1 million for the thirty-nine weeks ended December 29, 2018. Consolidated same store sales