Sales for the year ended December 31, 2021, increased $1.72 billion, or 15%, to $13.33 billion from $11.60 billion for the same period one year ago. Gross profit for the year ended December 31, 2021, increased 15% to $7.02 billion (or 52.7% of sales) from $6.09 billion (or 52.4% of sales) for the same period one year ago. SG&A for the year ended December 31, 2021, increased 12% to $4.10 billion (or 30.8% of sales) from $3.67 billion (or 31.6% of sales) for the same period one year ago. Operating income for the year ended December 31, 2021, increased 21% to $2.92 billion (or 21.9% of sales) from $2.42 billion (or 20.8% of sales) for the same period one year ago.
Net income for the year ended December 31, 2021, increased $412 million, or 24%, to $2.16 billion (or 16.2% of sales) from $1.75 billion (or 15.1% of sales) for the same period one year ago. Diluted earnings per common share for the year ended December 31, 2021, increased 32% to $31.10 on 70 million shares versus $23.53 on 74 million shares for the same period one year ago.
“As we look forward to 2022,” Mr. Johnson continued, “we remain confident in the strength of our Team and our industry, and our 2022 financial guidance reflects our expectations for continued strong customer demand, as well as our planned strategy to further invest in pricing on the professional side of our business. We continually monitor the competitive landscape in our industry and have been extremely pleased with our ability to grow both our DIY and professional business at record levels over the last two years; however, we believe we have an opportunity to accelerate our professional share gain through targeted competitive adjustments to our pricing strategy. We have incorporated our expectations for continued robust demand on both sides of our business and the anticipated sales lift from our professional pricing initiative in establishing our 2022 comparable store sales guidance range of 5% to 7%. Our gross profit and operating profit guidance ranges also reflect the rollout of our professional pricing initiative, which we strongly believe will further solidify our competitive position and drive long-term profitable growth.”
4th Quarter and Full-Year Comparable Store Sales Results
Comparable store sales are calculated based on the change in sales for U.S. stores open at least one year and exclude sales of specialty machinery, sales to independent parts stores and sales to Team Members, as well as sales from Leap Day for the year ended December 31, 2020. Online sales for ship-to-home orders and pick-up-in-store orders for U.S. stores open at least one year are included in the comparable store sales calculation. Comparable store sales increased 14.5% for the fourth quarter ended December 31, 2021, on top of 11.2% for the same period one year ago. Comparable stores sales increased 13.3% for the year ended December 31, 2021, on top of 10.9% for the same period one year ago.
Share Repurchase Program
During the fourth quarter ended December 31, 2021, the Company repurchased 0.7 million shares of its common stock, at an average price per share of $637.15, for a total investment of $469 million. During the year ended December 31, 2021, the Company repurchased 4.5 million shares of its common stock, at an average price per share of $545.78, for a total investment of $2.48 billion. Subsequent to the end of the fourth quarter and through the date of this release, the Company repurchased an additional 0.3 million shares of its common stock, at an average price per share of $660.23, for a total investment of $215 million. The Company has repurchased a total of 85.9 million shares of its common stock under its share repurchase program since the inception of the program in January of 2011 and through the date of this release, at an average price of $197.48, for a total aggregate investment of $16.96 billion. As of the date of this release, the Company had approximately $1.79 billion remaining under its current share repurchase authorizations.