Gross Profit and Gross Margin
Gross profit of $525.5 million for the six months ended October 31, 2020 decreased $32.6 million, or 5.8%, compared to the six months ended October 31, 2019 primarily due to a decrease in sales volume due to the impact of the COVID-19 pandemic. Gross margin on net sales decreased to 32.5% for the six months ended October 31, 2020 compared to 32.7% for the six months ended October 31, 2019 primarily due to increased competition and product mix.
Selling, General and Administrative Expenses
Selling, general and administrative expenses of $371.5 million for the six months ended October 31, 2020 decreased $23.6 million, or 6.0%, compared to the six months ended October 31, 2019. Selling, general and administrative expenses were 23.0% of our net sales during the six months ended October 31, 2020 compared to 23.1% of our net sales during the six months ended October 31, 2019. The decrease was primarily driven by proactive actions taken to reduce costs in response to the COVID-19 pandemic, partially offset by deflationary market pricing of certain of our products and incremental costs as a result of the COVID-19 pandemic.
Depreciation and Amortization Expense
Depreciation and amortization expense was $54.3 million for the six months ended October 31, 2020 compared to $58.8 million for the six months ended October 31, 2019. The decrease was due to a $5.0 million decrease in amortization of definite-lived intangible assets, partially offset by a $0.5 million increase in depreciation expense. The decrease in amortization expense was primarily due to the time-based progression of our use of the accelerated method of amortization for acquired customer relationships. The increase in depreciation expense was primarily due to capital expenditures and acquisitions over the past year.
Interest Expense
Interest expense was $27.6 million during the six months ended October 31, 2020 compared to $35.8 million for the six months ended October 31, 2019. The decrease was primarily due to a decrease in the outstanding amount of debt and a decrease in interest rates.
Income Taxes
We recognized income tax expense of $17.9 million during the six months ended October 31, 2020 compared to $15.5 million during the six months ended October 31, 2019. Our effective tax rate was 24.3% and 22.3% for the six months ended October 31, 2020 and 2019, respectively. The change in the effective income tax rate was primarily due to the impact of state taxes, foreign taxes and stock-based compensation.
Net Income
Net income was $55.7 million during the six months ended October 31, 2020 compared to $54.0 million for the six months ended October 31, 2019. The increase in net income was primarily due to a decrease in interest expense, partially offset by a decrease in operating income, primarily resulting from lower net sales, and an increase in income taxes.
Adjusted EBITDA
Adjusted EBITDA of $165.6 million for the six months ended October 31, 2020 decreased $7.9 million, or 4.6%, from our Adjusted EBITDA of $173.5 million for the six months ended October 31, 2019. The decrease in Adjusted EBITDA was primarily due to the negative impacts of the COVID-19 pandemic on net sales, partially offset by operating expense containment measures and strength in the Canadian housing market. See “—Non-GAAP Financial Measures—Adjusted EBITDA,” below for how we define and calculate Adjusted EBITDA, reconciliations to net income and a description of why we believe these measures are useful.