must purchase a beverage to get the free donut. read on:
National Donut Day, celebrated this year on June 3, is a day to honor the donut’s place in America’s history and culture, and the happiness and fun donuts bring to people’s lives. Dunkin’ Donuts, America’s all-day, everyday stop for coffee, donuts and baked goods, is making it sweet and easy for anyone to enjoy National Donut Day in the best way possible: with a delicious, free donut. On June 3, participating Dunkin’ Donuts restaurants nationwide will offer guests a free donut of their choice (while supplies last) with the purchase of a beverage (excluding bottled cooler beverages).
National Donut Day, held the first Friday of June each year, was originally established in 1938 by the Chicago Salvation Army to honor women who served donuts to soldiers during World War I
Krispy Kreme also has a free donut offer: