DoomsdayWhat day of the week was it?
Type any date from 1583 to 9999, such as your birthday, a wedding or a day in history. You get the weekday, and the Doomsday method's working, so you could have done it in your head.
How to work it out in your head
Famous dates
- Sunday20 July 1969 · Moon landing
- Thursday9 November 1989 · Berlin Wall falls
- Thursday4 July 1776 · US Declaration of Independence
- Tuesday6 June 1944 · D-Day
- Monday15 April 1912 · Titanic sinks
- Saturday1 January 2000 · The millennium
- Friday29 June 2007 · First iPhone on sale
- Sunday26 December 1937 · John Conway born
- Tuesday29 February 2028 · Next leap day
How does this work?
Every weekday on this page comes from the Doomsday algorithm, which mathematician John Conway designed to be done in your head. It rests on one fact: in any year, 4/4, 6/6, 8/8, 10/10 and 12/12 all fall on the same weekday, which Conway called the year's doomsday. Every month has a date like that.
To find a weekday, you work out the year's doomsday from a weekday for the century and a small number for the year. Then you count from the nearest doomsday date in your month. The working above shows each step for the date you entered.
Why 1583?
The Gregorian calendar began in October 1582. Before that, and in some countries for much longer (Britain and its colonies until September 1752, Russia until 1918), dates were kept in the Julian calendar, which needs a different anchor. The Doomsday app teaches the Julian version too.
Want to do this without a phone? It takes about a dozen facts and a little practice. Start with the free guide, practise in the trainer, or learn it properly in the Doomsday app.
Stop looking it up.
Doomsday teaches you to name the weekday of any date in a few seconds.
