Day Finder
Work out which day of the week any date fell on, from 1900 to 2099. Learn the Doomsday trick from the explanation after every answer. Five dates daily.
How to play
- You are shown a date between 1900 and 2099. Choose the weekday you think it fell on.
- After each answer you see whether you were right and a step-by-step Doomsday explanation of how to get there in your head.
- Answer five dates to finish. Your score and the dates you missed are listed at the end.
- Share your result as a row of green and red squares.
Tips and strategy
- Every year has a doomsday: a weekday shared by 4 April, 6 June, 8 August, 10 October and 12 December. Learn those five dates first.
- Other easy anchors are 3 January (4 January in a leap year), the last day of February, 14 March, 9 May, 11 July, 5 September and 7 November.
- Once you have the anchor in a month, count the gap to your date in weeks and spare days.
- Practise on dates you know. Checking your own birthday is a good way to see the pattern.
FAQ
- What is the Doomsday rule?
- It is a method devised by the mathematician John Conway. Each year has a doomsday weekday, and certain memorable dates always land on it, so any other date is a short count away.
- Why only 1900 to 2099?
- Within those two centuries the rule uses just two century anchors, which keeps the mental arithmetic manageable.
- Are the answers checked against a real calendar?
- Yes. The correct weekday comes from the real Gregorian calendar, and the explanation is checked to agree with it.