Doomsday Weekday Calculator
Weekday, with the doomsday anchor
The Doomsday rule finds the weekday of any date using a single anchor day per year. Enter a date and this calculator returns its exact weekday instantly and shows that year's doomsday — the weekday shared by 4/4, 6/6, 8/8, 10/10 and 12/12 — so you can learn the mental method.
Doomsday Rule
Weekday the clever way
The weekday, and the Doomsday behind it
The Doomsday rule is a clever method for working out the day of the week for any date in your head. This calculator gives you the answer instantly and shows the “doomsday” — the weekday that certain easy-to-remember dates always fall on in a given year — so you can learn the trick as you go.
In every year, dates like 4/4, 6/6, 8/8, 10/10, 12/12 and the last day of February all share the same weekday: that year's doomsday. Once you know it, you can reason your way to any other date quickly.
Learning the method
This tool shows the doomsday for the year of your date and the weekday of the date itself, so you can check your own mental maths. For your birthday specifically, our guide covers what day of the week you were born on.
Why the Doomsday rule is worth knowing
Mental weekday calculation is a classic party trick, but it is also useful — planning around which day a future date lands on, checking historical dates, or settling an argument without a calendar. The beauty of Conway's method is that it needs only one memorised anchor per year and a little arithmetic, so with practice you can name the weekday of any date in a few seconds. This calculator gives the instant answer and shows the year's doomsday, so you can check your own working as you learn.
Related tools
For a straightforward weekday lookup with day-of-year and week number, use the day of the week calculator.
Common questions
What is the Doomsday rule?
What is a year's doomsday?
Does this calculate the weekday for me?
Is it accurate for old and future dates?
- Method: John Conway’s Doomsday algorithm on the proleptic Gregorian calendar.
- Reference: the Doomsday rule — each year’s anchor weekday, shared by 4/4, 6/6, 8/8, 10/10 and 12/12.
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