Day of the Week Calculator

About this calculator

This calculator determines which day of the week any calendar date falls on, using the same date-arithmetic logic as Zeller's congruence — accounting correctly for leap years and the Gregorian calendar's rules — so it works for dates far in the past or future, not just the current year.

It's used to check what weekday a historical event happened on, to figure out the weekday of a birthday or anniversary in a given year, or to plan an event on a specific future date without having to flip through a calendar.