There is no single, real “devil’s birthday” in any historical or religious sense; different cultures and jokes use the phrase in different ways, and sometimes people just say it about Halloween or random “unlucky” dates for fun or symbolism.

What people usually mean

  • Some English-speaking Christians and internet communities casually call Halloween (October 31) “the devil’s birthday,” but this is a modern myth and not part of official Christian teaching.
  • In Christian theology, Satan is a fallen angel, not a human with a literal birth date, so the idea of a calendar birthday is symbolic, not factual.

Actual “Devil’s Birthday” on the calendar

  • In Denmark and Norway, “Devil’s Birthday” (Danish/Norwegian: Fandens fødselsdag) is a humorous folk nickname for May 19, tied to old loan and interest payment dates that people dreaded.
  • The term appears in written Danish sources from at least the late 19th century, reflecting more of a joke about hated payment days than any occult belief.

Other dates you might hear

  • Some online discussions mention June 11 or December 11 as “the devil’s birthday,” again as dark humor around traditional tax or payment days.
  • Various modern blogs, videos, or sermons may pick different dates (like Halloween or nearby days) to make a point about evil, sin, or “counterfeit” holidays, but these are opinion-based, not historical facts.

TL;DR: If someone asks “when is the devil’s birthday,” the most concrete traditional answer from real-world custom is May 19 in Danish and Norwegian folk usage, while Halloween is only a modern mythic or rhetorical answer with no formal religious basis.

Information gathered from public forums or data available on the internet and portrayed here.