Day of the Week
What day any date falls on — including the day you were born.
About this tool
Pick any date and see its weekday instantly, with the distance from today and — for birthdays — which weekday your next one lands on. It handles the full calendar range, past and future, using the same Gregorian rules that govern real calendars.
The party trick: Doomsday
Mathematician John Conway invented a method that turns any date into its weekday in seconds of head-math. The spine: in any given year, an easily-memorised family of dates — 4/4, 6/6, 8/8, 10/10, 12/12, plus 9/5, 5/9, 7/11, 11/7 and the last day of February — all fall on the same weekday, the year's "doomsday". For 2026 that's Saturday. From the nearest anchor, any date is a small hop of adding and subtracting days mod 7. Practised doomsdayers do any date in under five seconds, and learning it teaches you more about the calendar's structure than any almanac — for instance why the 13th is fractionally more likely to fall on Friday than any other day (the 400-year Gregorian cycle isn't perfectly even: Friday wins 688 of the 4,800 month-13ths). Related date arithmetic: days between dates and business-day counts.
Frequently asked questions
How do I find what day I was born?
Pick your birth date above — the weekday appears instantly, along with how many days ago it was and what weekday your next birthday falls on.
What is the Doomsday rule?
Conway's mental method: dates like 4/4, 6/6, 8/8, 10/10, 12/12 and the last day of February all share one weekday each year. Anchor on that, then hop to any date by counting days mod 7.
Is Friday the 13th really more common?
Very slightly, yes: over the Gregorian calendar's 400-year cycle the 13th falls on Friday 688 times — more than any other weekday (Thursday manages 684). It's a quirk of the leap-year pattern, not a curse.
Why does my birthday's weekday shift each year?
A normal year is 52 weeks + 1 day, so the weekday advances one step — two after a leap day intervenes. That's also why calendars repeat exactly only every 28 years (usually).