Day of the week calculator
Which weekday any date falls on, from year 1 to 9999, with a mental-maths method you can follow along.
Day of the weekDateMath Pro
Date20 July 1969
Sunday
Sunday, 20 July 1969
Work it out yourself: the Doomsday rule
John Conway devised this method in 1973 and could reportedly name the weekday of any date in under two seconds. Step through it for the date above.
- Century anchor. For the 1900s the anchor is Wednesday. (Anchors cycle every 400 years: 1800s Friday, 1900s Wednesday, 2000s Tuesday, 2100s Sunday.)
- Year within the century: 69. 69 ÷ 12 = 5 remainder 9; 9 ÷ 4 = 2 (drop the fraction).
- Add them up. anchor + 5 + 9 + 2, reduced mod 7, lands on Friday: the doomsday of 1969.
- Nearest doomsday date in July. 11 July is a Friday.
- Count the gap. 20 − 11 = 9 days; Friday moved by 2 is Sunday.
Why weekdays drift
365 days is 52 weeks plus 1 day, so a date usually falls one weekday later each year, and two later after a 29 February. The full Gregorian cycle of 400 years is exactly 146,097 days, a whole number of weeks, so the calendar for 2426 will be identical to 2026's.
Questions people ask
What day of the week was I born?
Enter your date of birth and the calculator gives the weekday, using the Gregorian calendar for all years.
How can I work out the day of the week in my head?
Use John Conway's Doomsday rule: every year, certain easy dates (4/4, 6/6, 8/8, 10/10, 12/12, 9/5, 5/9, 7/11, 11/7 and the last day of February) all fall on the same weekday, the year's "doomsday". Find the doomsday, then count from the nearest of those dates. The step-through on this page shows each stage.
Does this work for dates before 1582?
It uses the proleptic Gregorian calendar. Countries switched from the Julian calendar at different times (Britain and its colonies in 1752), so for older historical dates recorded in Julian style, convert them first.
What weekday does a date fall on in a future year?
Each date moves forward one weekday per year, or two when a 29 February is crossed. That's why the calendar repeats exactly only every 400 years.
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