Wednesday, September 18, is National Cheeseburger Day, and fast-food chains like McDonald’s, Burger King, and Wendy’s offer major discounts and freebies to celebrate. McDonald's is offering 50-cent double cheeseburgers exclusively through its mobile app. Burger King is giving away free cheeseburgers to members of its Royal Perks loyalty program with any purchase of $1 or more on National Cheeseburger Day. At Wendy’s, you can score a junior bacon cheeseburger for just 1 cent with any purchase made through the Wendy's app. Buffalo Wild Wings is offering a buy one, get one free cheeseburger deal for members of their Blazin' Rewards loyalty program. Denny’s Rewards members can receive 20% off any burger on the menu. Smashburger is offering $5 classic single burgers all-day.