And for 65 years, we've created iconic experiences for billions of people around the world.
For the past 18 months, our digital customer engagement, global marketing, data analytics and restaurant solutions teams have worked to standardize our infrastructure and align the system against some common frameworks.
He's been an important part of the McDonald's system for more than 20 years at every level.
McSpicy launched in China over 20 years ago, and customers can now enjoy this great-tasting sandwich in multiple markets around the world.
And earlier this month, we were proud to launch our new loyalty program, MyMcDonald's Rewards, in the U.S. The loyalty of every McDonald's fans has been unmatched for 65 years.
We already have over 22 million active MyMcDonald's users in the U.S., with over 12 million enrolled in our new loyalty program, MyMcDonald's Rewards.
Our digital systemwide sales across our top six markets were nearly $8 billion in the first half of 2021, a 70% increase versus last year.
Over 80% of our restaurants across 100 markets globally now offer delivery.
Today, about 70% of our dining rooms in the U.S. are open.
By Labor Day, barring resurgences, it will be nearly 100%.
I'm pleased to share that global comp sales were up 40% in the second quarter or 7% on a two-year basis.
In the U.S. our momentum continued with Q2 comp sales up 26% or 15% on a two-year basis, our strongest quarterly two-year growth in over 15 years.
Our performance in the U.S. is the result of an accumulation of decisions that we've made over the last 18 months.
This includes an advertising rehit of our Crispy Chicken Sandwich, which continues to perform at an elevated level and the success of our BTS meal.
Comp sales were up 75% in the quarter or nearly 3% on a two-year basis as we lapped the peak in 2020 restaurant closures.
The market benefited from continued growth in delivery and successful marketing and core menu news, including the BTS Famous Orders and 50th Birthday Big Mac promotion.
Comp sales in the International Developmental Licensed segment were up 32% for the quarter or relatively flat on a two-year basis.
Japan maintained momentum in Q2 with comps up nearly 10%, achieving an impressive 23 consecutive quarters of comp sales growth.
In addition, China surpassed the 4,000-restaurant mark in June and is now on pace to open over 500 new restaurants this year.
This quarter, the BTS Famous Order took that ambition global, connecting our marketing, core menu and digital strategies in 50 markets.
Adjusted earnings per share in Q2 was $2.37, which excludes a gain on the further sale of some of our ownership in McDonald's Japan and a onetime income tax benefit in the U.K. In year-to-date, adjusted operating margin was 43%, reflecting improved sales performance across all segments and higher other operating income compared to last year.
Total restaurant margin dollars grew $1.3 billion in constant currencies with improvement in both franchised and company-operated restaurant margins, mostly driven by higher comp sales as a result of COVID-19 impact last year.
G&A decreased 1% in constant currencies for the quarter, primarily due to lapping our $160 million incremental marketing investment last year, offset by higher incentive-based compensation and increased spend in restaurant technology.
Our adjusted effective tax rate was 21.7% for the quarter.
And we're projecting the tax rate for the back half of 2021 in the range of 21% to 23%.
And finally, foreign currency translation benefited Q2 results by $0.13 per share.
Based on current exchange rates, we expect FX to benefit earnings per share by about $0.03 to $0.05 for Q3, with an estimated full year tailwind of $0.20 to $0.22.
I'm proud of all that we've accomplished during the past 18 months.
For 65 years, the one unassailable truth about McDonald's is that we get better together.
That's why in May, we announced a 10% increase in the average hourly wage at our company-owned restaurants in the U.S., with the goal to get to a $15 an hour wage by 2024.
Today, 23% of our U.S.-based suppliers come from diverse backgrounds, more than double the industry average.
We have set a goal to increase purchases of goods and services from diverse-owned suppliers by 10% over the next four years.
That will put us in a position where 1/4 of our U.S. spend is with diverse-owned suppliers by 2025.
I'm amazed with everything that our system has accomplished over the past 18 months, and we can't wait to write the next great chapter of the McDonald's story together.

Summary:
This includes an advertising rehit of our Crispy Chicken Sandwich, which continues to perform at an elevated level and the success of our BTS meal.
The market benefited from continued growth in delivery and successful marketing and core menu news, including the BTS Famous Orders and 50th Birthday Big Mac promotion.
Adjusted earnings per share in Q2 was $2.37, which excludes a gain on the further sale of some of our ownership in McDonald's Japan and a onetime income tax benefit in the U.K. In year-to-date, adjusted operating margin was 43%, reflecting improved sales performance across all segments and higher other operating income compared to last year.
And finally, foreign currency translation benefited Q2 results by $0.13 per share.