Holy Birthday, Batman! We all know the Dark Knight turns 75 this year, but the day and month are up for debate. Although DC Comics has decided that Batman's 75th anniversary will be celebrated this Wednesday, it isn't even near the most liberal estimates of when his first comic appeared on shelves. DC has admitted to the New York Daily News that they chose July 23 because it coincides with the preview night of Comic-Con. Wednesday's anniversary is also a part of a two-phase anniversary plan, involving Comic-Con, comic book stores across the US, and libraries.
Nonetheless, some fans probably want to know when Batman was really born, and unfortunately, the Internet has been confused on the topic. Batman first appeared in Detective Comics #27, which was definitely released in 1939. First of all, the issue is dated "May 1939," which seems to imply that it would have hit newsstands some time in May. However, it's clearly more complicated than that: DC started the bat-festivities on March 30 because they claimed it was "common practice in 1939" to release comics far before their printed date. And MTV confirms that one of the print dates on this comic book's copyright is March 30, confirming that Batman probably popped onto newsstands somewhere around that date. However, as Bleeding Cool points out, individual issues could have been distributed anywhere from March 30 (the first legally-available date) through May. Also, an ad for Batman's arrival appeared in Action Comics #12, which has a publication date a week before the sacred March 30.
So Batman's birthdate fundamentally depends on your geographic area, definition of "arrival" or "publication date" and willingness to accept DC's fabricated holiday. So instead of a day let's all continue to celebrate 2014 as the 75th Anniversary of The Year of Great Comics. Otherwise it gets confusing.