Our domestic same-store sales were an impressive 4.3% this quarter on top of last year's historic 21.8% growth.
Our growth rates for retail and commercial were both strong with domestic commercial growth north of 21%.
Our commercial business set a record this quarter with $1.2 billion in sales for the quarter, an incredible accomplishment.
Additionally, we reached a new milestone in commercial sales surpassing $3 billion for the year, finishing with over $3.3 billion in annual sales versus $2.7 billion in sales a year ago, an impressive 23% increase.
We set new records in annual sales volumes per store reaching $12,600 for the year, up from $10,600 just last year.
We ran a roughly flat comp this quarter after increasing well over 20% in last year's fourth quarter.
The first eight weeks of the quarter, our comp was 3.1%.
In the last eight weeks, our comp averaged 5.5%.
Given the dynamics of the past 18 months, we like others who benefited from the lumpiness of the pandemic sales, believe it is more insightful to look at a two-year stack comp.
For Q4, our two year comp was 26%.
On a two-year basis, our cadence for each four week period of the quarter was 26.8%, 28.2%, 25.5% and 24%.
Regarding the quarter's traffic versus ticket growth, our retail traffic was down roughly 4%, while our retail ticket was up 3%.
Across both our retail and commercial customer basis, we saw the Midwest, Mid-Atlantic and Northeastern markets underperform, roughly 400 basis points in comp versus the remainder of the country.
We have been very pleased that we have retained the roughly 10% market share we gained in our retail sales floor business last year.
On Q2's call, we shared that we would provide every AutoZoner with a $100 incentive once they completed their vaccination for COVID-19, that's every AutoZoner including part-timers.
We spent another $2.7 million in the fourth quarter reimbursing our AutoZoners for the vaccine.
We are strongly encouraging our AutoZoners to get the vaccine as our culture and values of taking care of one another have been on display for the past 18 months.
Our same-store sales were up 4.3% versus last year's fourth quarter.
Our net income was $786 million and our earnings per share was $35.72 a share, 15.5% above last year's fourth quarter.
Commercial total sales grew approximately 21%.
We averaged $74 million in weekly sales, which was approximately $14,400 in sales per program per week, which was easily an all-time record for us.
I'll remind you that this is a highly fragmented $75 billion market and we believe our product and service offerings provide us a tremendous opportunity to significantly grow sales and market share over time.
This quarter we saw our retail sales impacted positively by about 2% year-over-year from inflation, while our cost of goods was basically flat.
For the quarter, total auto parts sales, which includes our Domestic, Mexico and Brazil stores were $4.8 [Phonetic] billion, up 8%.
And for the total year, our total auto parts sales were $14.4 billion, up 15.9%.
Starting with our commercial business, for the fourth quarter our domestic DIFM sales increased 21% to $1.2 billion and were up 31% on a two year stack basis.
Sales to our DIFM customers represented 24% of our total sales and our weekly sales per program were $14,400, up 18% as we averaged $74 million in total weekly commercial sales.
Once again, our growth was broad-based as national and local accounts all grew over 20% in the quarter.
For the full-year, our commercial sales grew 22.6% and 29% on a two-year stack basis.
We now have our commercial program in over 86% of our domestic stores and we're focused on building our business with national, regional and local accounts.
This quarter, we opened 72 net new programs, finishing with 5,179 total programs.
We now have 58 mega hub locations and we expect to open approximately 20 more over the next 12 months.
As a reminder, our mega hubs typically carry roughly 100,000 SKUs and drive tremendous sales lift inside the store box, as well as serve as the fulfillment source for other stores.
I will remind you that our current mega hub strategy envisions our expansion to a total of 100 to 110 mega hubs.
On the retail side of our business, our domestic retail business was down just 40 basis points, but up 23.4% on a two year stack.
For the full-year, the retail business was up 11.2% and 18.7% on a two year stack basis.
The business has been remarkably resilient as we have gained and maintained nearly 300 points of market share since the start of the pandemic.
During the quarter, we opened 29 new stores in Mexico to finish with 664 stores and five new stores in Brazil to finish with 52.
For the quarter, our gross margin was down 82 basis points, driven primarily by the accelerated growth in our commercial business, where the shift in mix coupled with the investment in our initiatives drove margin pressure, but increased our gross profit dollars by 6.4%.
I mentioned on last quarter's call that we expected to have our gross margin down in a similar range to our third quarter, where we were down 118 basis points.
Our expenses were, up 9.2% versus last year's Q4 as SG&A as a percentage of sales deleveraged 33 basis points.
Moving to the rest of the P&L, EBIT for the quarter was just over $1 billion, up 2.6% versus prior year's quarter, driven by strong topline growth.
EBIT for fiscal year '21 was just over $2.9 billion, up 21.8% versus fiscal year '20.
Interest expense for the quarter was just over $58 million, down 11.5% from Q4 a year ago as our debt outstanding at the end of the quarter was just under $5.3 billion versus just over $5.5 billion last year.
We're planning interest in the $46 million to $48 million range for the first quarter of fiscal 2022 versus $46 million in last year's first quarter.
For the quarter, our tax rate was 20.3% versus 22.3% in last year's fourth quarter.
This quarter's rate benefited 215 basis points from stock options exercised, while last year it benefited 35 basis points.
For the first quarter of 2022, we suggest investors model us at approximately 23.6% before any exemptions on credits due to stock option exercises.
Net income for the quarter was $786 million, up 6.1% versus last year's fourth quarter.
Our diluted share count of 22 million was lower by 8.1% from last year's fourth quarter.
The combination of higher earnings and lower share count drove earnings per share for the quarter to $35.72, up 15.5% over the prior year's fourth quarter.
Net income per share for fiscal year '21 was $95.19, up a remarkable 32.3%, reflecting our outstanding topline performance and lower share count.
For the fourth quarter, we generated $1.3 billion of operating cash.
Regarding our balance sheet, we now have nearly $1.2 billion in cash on the balance sheet and our liquidity position remains strong.
Total inventory increased 3.7% over the same period last year, driven by new stores.
Net inventory defined as merchandise inventories less accounts payable on a per store basis was a negative $203,000 versus negative $104,000 last year and negative $167,000 last quarter.
As a result, accounts payable as a percent of gross inventory finished the quarter at 129.6% versus last year's Q4 of 115.3%.
We repurchased $900 million of AutoZone stock in the quarter.
As of the end of the fiscal quarter, we had approximately 21.1 million shares outstanding.
At quarter end, we had just over $418 million remaining under our share buyback authorization and over $900 million of excess cash.
For the full-year, we bought back $3.4 billion of stock or approximately 2.6 million shares.
The powerful free cash flow we have generated this year combined with excess cash carried over from last year has enabled us to buyback over 11% of our shares outstanding at the beginning of the year.
We have bought back nearly 90% of the shares outstanding of our stock since our buyback inception in 1998, while investing in our existing assets and growing our business.
So, to wrap up, we had another very strong quarter highlighted by strong comp sales, which drove a 6.1% increase in net income and a 15.5% increase in EPS.
We are also targeting to open 20 new domestic mega hubs in the US that will enhance our ability and support growth in our retail and commercial businesses.
We will open approximately 200 new stores throughout the Americas with notable acceleration in our Brazil business.

Summary:
Our domestic same-store sales were an impressive 4.3% this quarter on top of last year's historic 21.8% growth.
Our same-store sales were up 4.3% versus last year's fourth quarter.
Our net income was $786 million and our earnings per share was $35.72 a share, 15.5% above last year's fourth quarter.
The combination of higher earnings and lower share count drove earnings per share for the quarter to $35.72, up 15.5% over the prior year's fourth quarter.
Total inventory increased 3.7% over the same period last year, driven by new stores.