13 weeks ended April 30, 2022, compared to 38.9% for the 13 weeks ended May 1, 2021. The increase in gross profit margin was primarily due to leverage in fixed costs, strong growth in other revenue, and favorable channel mix shifts, partially offset by deleverage in merchandise margins.
Selling, general and administrative expenses
Selling, general and administrative (SG&A) expenses increased $57.1 million or 12.9%, to $501.0 million for the 13 weeks ended April 30, 2022, compared to $443.9 million for the 13 weeks ended May 1, 2021. SG&A expenses as a percentage of net sales decreased to 21.4% for the 13 weeks ended April 30, 2022, compared to 22.9% for the 13 weeks ended May 1, 2021, primarily due to lower marketing expenses and leverage in store payroll and benefits due to higher sales, partially offset by deleverage in corporate overhead due to strategic investments.
Pre-opening expenses
Pre-opening expenses were $2.3 million for the 13 weeks ended April 30, 2022 compared to $4.6 million for the 13 weeks ended May 1, 2021.
Interest expense, net
Interest expense, net of $0.4 million for the 13 weeks ended April 30, 2022 was consistent with the 13 weeks ended May 1, 2021. Interest expense represents interest on borrowings and fees related to the credit facility. We did not have any outstanding borrowings on the credit facility as of April 30, 2022 and May 1, 2021.
Income tax expense
Income tax expense of $105.9 million for the 13 weeks ended April 30, 2022 represents an effective tax rate of 24.2%, compared to $74.7 million of income tax expense representing an effective tax rate of 24.5% for the 13 weeks ended May 1, 2021.
Net income
Net income was $331.4 million for the 13 weeks ended April 30, 2022, compared to $230.3 million for the 13 weeks ended May 1, 2021. The increase in net income is primarily related to the $187.2 million increase in gross profit, partially offset by the $57.1 million increase in SG&A expenses and the $31.2 million increase in income tax expense.
Liquidity and capital resources
Our primary sources of liquidity are cash and cash equivalents, cash flows from operations, and borrowings under our credit facility. The most significant components of our working capital are merchandise inventories and cash and cash equivalents reduced by accounts payable, accrued expenses and deferred revenue. As of April 30, 2022, January 29, 2022, and May 1, 2021, we had cash and cash equivalents of $654.5 million, $431.6 million, and $947.5 million, respectively.
Our primary cash needs are for rent, capital expenditures for new, remodeled, and relocated stores, increased merchandise inventories related to store expansion and new brand additions, supply chain improvements, share repurchases, and continued improvement in our information technology systems.
Our most significant ongoing short-term cash requirements relate primarily to funding operations (including expenditures for lease expenses, inventory, labor, distribution, advertising and marketing, and tax liabilities) as well as periodic spend for capital expenditures, investments, and share repurchases. Our working capital needs are greatest from August through November as a result of inventory build-up during this period for the holiday season.
Long-term cash requirements primarily relate to funding lease expenses and other purchase commitments.