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Day of the Week Calculator
What day was it? Pick any date from year 1 to 9999.
July 20, 1969 was a
Sunday
- Day of year
- 201
- ISO week
- 29 (1969)
- Which Sunday
- 3rd of July
- Days ago
- …
Do it in your head: the Doomsday rule
Every year, certain easy dates all share one weekday, the year's "doomsday": 4/4, 6/6, 8/8, 10/10, 12/12, 9/5, 5/9, 7/11, 11/7, and the last day of February. Find that weekday, then count from the nearest one.
- Century anchor. 1900s start from Wednesday (1900s Wednesday, 2000s Tuesday; the pattern repeats every 400 years).
Change the date above and step through again; it works for every year the calculator accepts.
Common uses
- What day was I born? Enter your birth date. You'll also see the next years your birthday lands on the same weekday.
- Planning ahead. Check whether a deadline, wedding date or anniversary falls on a weekend before you commit.
- History. The Moon landing (20 July 1969) was a Sunday; the fall of the Berlin Wall (9 November 1989) a Thursday.
Need a whole month rather than one date? Use the perpetual calendar.
Questions people ask
How do I find what day of the week I was born?
Enter your date of birth above. The calculator shows the weekday, how many of that weekday have passed since, and which upcoming birthdays land on the same weekday.
How does the calculator work?
It counts the days between your date and a known reference (1 January 1970, a Thursday) and takes the remainder after dividing by 7. The Doomsday method below reaches the same answer in your head.
Who invented the Doomsday rule?
The mathematician John Horton Conway published it in 1973, building on Lewis Carroll's earlier method. Conway reportedly trained himself to answer in under two seconds.
What about dates before 1582?
The result uses the proleptic Gregorian calendar (the modern calendar extended backwards). Historical sources before the switch usually used the Julian calendar, which gives a different weekday for the same written date; our date converter shows both.