That’s right, Superman’s (canonical/in-universe) birthday falls on February 29th, a leap year. Originally started as a joke, Superman’s birthday was decided by the folks at DC due to the fact that he barely ages. Having his birthday fall on a leap year means that he’s only gaining one year instead of four, hence his perpetual youthfulness.
Despite the slightly humorous origin, comic fans and writer have been celebrating the Man of Steel’s birthday ever since. Comicbook.com gave a detailed take on the son of Krypton’s birthday:
For years, both Superman’s age and birthday have been variable in the comics, but the most consistently used birthday for Superman is February 29. The in-real-life joke is that since Superman never seems to age, it makes sense that he has a birthday that only comes around once every four years. In the comics, there was at one point a similar logic that held Krypton’s year was significantly longer than Earth’s.
While Superman’s birthday falls on every leap year, Clark Kent’s birthday on the hand is much easier to celebrate. His birthday falls on June 18th, the day when the Kents first found the rocket carrying young Kal-El.
Once again, happy Birthday to Superman and we look forward to another one in four years!