Datetime Tools
Day of the week you were born.
Enter your birthdate and we'll tell you exactly what day of the week it fell on — calculated from the real calendar, not a lookup table.
Inputs
Result
Enter a birthdate and press Find the day.
How it works
This tool builds a real JavaScript Date from the day, month, and year you enter and reads its day-of-week directly from the browser's own calendar implementation, which correctly follows the Gregorian calendar — including every leap year rule (divisible by 4, except centuries not divisible by 400). Nothing is hand-rolled or approximated.
Under the hood, that calculation is mathematically equivalent to Zeller's congruence, the classic formula for computing the day of the week for any Gregorian (or Julian) calendar date from its day, month, and year. If you're curious how it works by hand: Zeller's congruence adjusts for the fact that January and February are treated as the 13th and 14th months of the previous year (so the leap day doesn't shift months before it), then combines the day, a month-based term, and terms for the year and century, all reduced modulo 7 to land on a weekday.
Sanity-checked against well-known dates: July 4, 1976 (the US Bicentennial) lands on a Sunday, January 1, 1970 (the Unix epoch) lands on a Thursday, and January 1, 2000 lands on a Saturday — all matching the historical record.