According to 1977’s “Batman Family” #11 and the 1976 DC Comics wall calendar, traditionally today is Batman’s fictional, in-universe birthday. The Dark Knight’s first comic appearance was in May 1939’s “Detective Comics” #27. However, it’s nice to imagine Bats celebrates his birthday near his pal’s, Superman (which is traditionally February 29 of all dates).
According to astrology, Batman is a Pisces.
Besides the aforementioned “Batman Family” story, there’s a few other stories revolving around Bruce’s birthday. One is in “DC Super Friends” #15 from 2009. Comics Should Be Good went into this one at length.
Another is in “Star Spangled Comics” #91 from April 1949. “Star Spangled Comics” featured a series of Robin-starring stories in the late 1940s/early 1950s. Of course, being a Golden Age story, this one revolves around the Batman of Earth-Two’s birthday. The Golden Age Batman’s birthday is on April 7, different from his modern counterpart.
If you’re wondering about the rest of the (classic) Batman family, their birthdates:
- Commissioner Gordon: January 5
- Catwoman: March 14
- Alfred Pennyworth: April 8
- The Penguin: July 26
- The Joker: August 1
- Barbara Gordon (Batgirl/Oracle): September 23
- Dick Grayson (Robin/Nightwing): November 11
- The Scarecrow: November 16
- Two-Face: December 7
Oddly, Two-Face’s birthday isn’t on a date associated with the number two or concept of duality.
Unusual for this calendar, Dick’s birthday falls on an actual holiday, Veterans’ Day. That said, Barbara’s birthday falls on or around the start of fall (in the northern hemisphere).
I assume the Joker’s birthday, like his real name, is unknown, and it’s a date he picked on his own. That said, the Clown Prince of Crime did “celebrate” his birthday at least once, in “Batman” #321 (March 1980). In that story, the Joker kidnaps various Batman supporting characters, including Dick, Alfred, and Commissioner Gordon; they end up tied to a birthday cake-themed death trap. Of course, the Caped Crusader rescues all parties involved.