We continue to retain about 80% of digital sales but have now recovered nearly 80% of in-restaurant sales.
For the quarter, we reported record quarterly sales of $2 billion, representing 21.9% year-over-year growth, which was fueled by a 15.1% increase in comparable restaurant sales.
Restaurant level margin of 23.5% was 400 basis points higher than the 19.5% we reported last year.
Earnings per share adjusted for unusual items of $7.02, representing an increase of 86.7% year-over-year.
Digital sales growth of 8.6% year-over-year, representing 42.8% of sales and we opened 41 new restaurants, including 36 with a Chipotlane.
While we regularly get asked, what's next, I believe our current growth drivers have plenty of runway and will be critical to us reaching our longer-term goal of 6,000 restaurants in North America with AUVs above $3 million and improving returns on invested capital.
Over the past 18 months, we've made operational adjustments to adapt to our constantly changing environment in support of our in-restaurant business as well as our record-breaking digital business.
Our frontline represented nearly 60% of our business or $1.1 billion of sales for the quarter.
During the third quarter, digital sales grew nearly 9% year-over-year to $840 million and represented 43% of sales.
In fact, our year-to-date digital sales of nearly $2.7 billion are just slightly below the $2.8 billion we achieved during all of last year.
Currently, about 65% of our guest use in-restaurant as their main access point, nearly 20% use digital as their primary channel, and the remaining 15% to 20% use both channels.
Speaking of the loyalty program, we're excited to have more than 24.5 million members, many of whom are new to the brand.
For example, we use numerous campaigns to stay relevant via important sporting events such as the basketball championships, where we hit $1 million worth of free burritos in our TV advertising.
We're pleased to report solid third quarter results with sales growing 21.9% year-over-year to $2 billion as comp sales grew 15.1%.
Restaurant level margin of 23.5% expanded 400 basis points over last year, and earnings per share adjusted for unusual items was $7.02, representing 86.7% year-over-year growth.
The third quarter had a GAAP tax benefit that I'll discuss shortly, which is partially offset by expenses related to a previously disclosed modification to our 2018 performance share and transformation expenses, which netted to positively impact our earnings per share by $0.16 leading to GAAP earnings per share of $7.18.
But given our strong underlying business momentum, we expect our comp to be in the low-to-mid double digits, which is encouraging considering that will be about 200 basis points less than pricing contribution during Q4 versus Q3 as we've lap some of our delivery menu price increases.
Our supply chain team has done an outstanding job, navigating the numerous industrywide disruption, which led to food costs being 30.3% in Q3, a decrease of 200 basis points from last year.
In addition, Q4 will also include the higher cost brisket LTO, which collectively will result in our food costs being in the low-31% range for the quarter.
Labor costs for the third quarter were 25.8%, an increase of about 40 basis points from last year.
This increase was driven by our strategy to increase average nationwide wages to $15 per hour, which is partially offset by menu price increases, sales leverage, and a one-time employee retention credit.
Given ongoing elevated wage inflation and greater new unit openings, we expect labor costs to be in the mid-26% range in Q4.
Other operating costs for the quarter were 15.1%, a decrease of 170 basis points from last year due primarily to price and sales leverage.
Marketing and promo costs for the quarter were 2.4%, about 20 basis points lower than we spent last year.
As a result, we anticipate marketing expense to be around 4% in Q4 to support Smoked Brisket and for the latest brand messaging under our Behind The Foil campaign.
For the full year 2021, marketing expense is expected to remain right about 3% of sales.
Overall, other operating costs are expected to be in the mid-16% range for the fourth quarter.
Looking at overall restaurant margins, we expect Q4 to be in the 20% to 21% range.
Our Q4 underlying margin would be around 22% when you normalize marketing spend and remove the temporary headwind from the brisket LTO.
G&A for the quarter was $146 million on a GAAP basis or $137 million on a non-GAAP basis, including $7.6 million for the previously mentioned modification for 2018 performance shares, and $1.6 million related to transformation and other expenses.
G&A also includes about $100 million in underlying G&A, about $28 million related to non-cash stock compensation, about $8.5 million related to higher performance-based bonus accruals and payroll taxes and equity vesting, and stock option exercises, and roughly, $600,000 related to our upcoming all-manager conference.
Looking to Q4, we expect our underlying G&A to be right around $101 million as we continue to make investments primarily intact to support ongoing growth.
We anticipate stock comp will likely be around $27 million in Q4, although this amount could move up or down based on our actual performance.
We also expect to recognize around $5.5 million related to performance-based bonus expense and employer taxes associated with shares that vest during the quarter as well as about $1.5 million related to our all-manager conference.
Our effective tax rate for Q3 was 14.7% on a GAAP basis and 19.7% on a non-GAAP basis.
For Q4, we continue to estimate our underlying effective tax rate to be in the 25% to 27% range, though it may vary based on discrete items.
Our balance sheet remains healthy as we ended Q3 with $1.2 billion in cash, restricted cash and investments with no debt along with a $500 million untapped revolver.
During the quarter, we repurchased $99 million of our stock at average price of $1,813 and we expect to continue using excess free cash flow to opportunistically repurchase our stock.
During Q3, despite a few delays in opening timeline, we opened 41 new restaurants with 36 of these including a Chipotlane.
In fact, we currently have more than 110 restaurants under construction, and while timing is somewhat unpredictable, this gives us confidence in ending the year at or slightly above the 200 new restaurants with now more than 75% including a Chipotlane versus our prior expectation of 70%.
As of September 30th, we had a total of 284 Chipotlanes, including 12 conversions and 8 relocations.

Summary:
For the quarter, we reported record quarterly sales of $2 billion, representing 21.9% year-over-year growth, which was fueled by a 15.1% increase in comparable restaurant sales.
Restaurant level margin of 23.5% was 400 basis points higher than the 19.5% we reported last year.
Earnings per share adjusted for unusual items of $7.02, representing an increase of 86.7% year-over-year.
Digital sales growth of 8.6% year-over-year, representing 42.8% of sales and we opened 41 new restaurants, including 36 with a Chipotlane.
We're pleased to report solid third quarter results with sales growing 21.9% year-over-year to $2 billion as comp sales grew 15.1%.
Restaurant level margin of 23.5% expanded 400 basis points over last year, and earnings per share adjusted for unusual items was $7.02, representing 86.7% year-over-year growth.
The third quarter had a GAAP tax benefit that I'll discuss shortly, which is partially offset by expenses related to a previously disclosed modification to our 2018 performance share and transformation expenses, which netted to positively impact our earnings per share by $0.16 leading to GAAP earnings per share of $7.18.
But given our strong underlying business momentum, we expect our comp to be in the low-to-mid double digits, which is encouraging considering that will be about 200 basis points less than pricing contribution during Q4 versus Q3 as we've lap some of our delivery menu price increases.
Our supply chain team has done an outstanding job, navigating the numerous industrywide disruption, which led to food costs being 30.3% in Q3, a decrease of 200 basis points from last year.
Other operating costs for the quarter were 15.1%, a decrease of 170 basis points from last year due primarily to price and sales leverage.
For Q4, we continue to estimate our underlying effective tax rate to be in the 25% to 27% range, though it may vary based on discrete items.
In fact, we currently have more than 110 restaurants under construction, and while timing is somewhat unpredictable, this gives us confidence in ending the year at or slightly above the 200 new restaurants with now more than 75% including a Chipotlane versus our prior expectation of 70%.