Whataburger will celebrate its 73rd birthday Tuesday, Aug. 8, a date the San Antonio-based chain is declaring the first-ever “National Whataburger Day.” The cool news is that the company is getting the party started with free hamburgers for the faithful. On August 7 and 8, those active on its Whataburger Rewards app will receive an in-app offer for a free Whataburger with no purchase necessary. What does it mean to be an “active” user, you may ask?