What it is for
This calculator instantly tells you what day of the week (Sunday through Saturday) any date falls on — past, present or future — handy for checking the weekday of an old birthday, a historical date, or planning future events.
How the calculation works
The calculation uses the browser's own calendar system, which already accounts for leap years and Gregorian calendar rules, ensuring accuracy for any date within the supported range.
Fun fact
The Gregorian calendar, used today across most of the world, repeats on a 400-year cycle — meaning the pattern of weekdays for each date repeats exactly every 400 years.
Frequently asked questions
Does this tool work for very old dates?
It works well for dates within the modern Gregorian calendar (from 1582 onward); for earlier dates, results may not match the historical calendars actually used at the time.
Can I look up future dates?
Yes, the calculator works equally well for any future date.
Does the result account for leap years?
Yes, the weekday calculation automatically accounts for leap years.