Day of the week calculator
4 July 1776 was a Thursday. The page gives the day for any date and then writes out Conway’s Doomsday rule underneath, because the answer is on every phone and the method is not — and the method is what lets you do it in your head for the rest of your life.
What day any date fell on — with Conway's Doomsday rule written out underneath, because the word itself is on every phone and the method is not.
Checked against every date across twelve years · How we check
That day was a
Thursday
Day 239 of 2026, ISO week 35.
How to do it in your head
| Anchor for the 2000s | Tuesday |
| Doomsday for 2026 | Saturday |
| A doomsday date in this month | 8 |
| Days from there to your date | +19 |
| Landing on | Thursday |
Every year has one weekday — its doomsday — shared by 4/4, 6/6, 8/8, 10/10, 12/12, 5/9, 9/5, 7/11 and 11/7. Find it once and every date in the year is a short hop from the nearest of those.
The dates worth memorising
The whole trick rests on a handful of dates that share a weekday within any year. The even months pair with themselves — 4/4, 6/6, 8/8, 10/10, 12/12 — and the odd ones pair across: 5/9 and 9/5, 7/11 and 11/7. Conway's mnemonic for the second set is “I work from 9 to 5 at the 7-11”. March is the 14th, which is Pi Day and easy to keep.
Learn those, learn the four century anchors, and the rest is adding a small number and taking the remainder on division by seven. It is the only mental calendar method simple enough that people actually retain it, which is why it is worth printing rather than hiding behind an answer.
Questions people actually ask
- What is the Doomsday rule?
- A mental method invented by John Conway. Every year has one weekday — its doomsday — that a set of easily remembered dates all fall on: 4/4, 6/6, 8/8, 10/10, 12/12, and the pairs 5/9, 9/5, 7/11 and 11/7. Find that weekday for the year, hop from the nearest of those dates to yours, and you have the answer. With practice it takes a few seconds.
- How do I find the doomsday for a year?
- Start from the century anchor — Tuesday for the 2000s, Wednesday for the 1900s, Friday for the 1800s, Sunday for the 2100s. Take the last two digits of the year, divide by 12 and keep the quotient, the remainder, and the remainder divided by four. Add all three to the anchor and reduce modulo seven. For 2026 that lands on Saturday.
- Why are January and February different?
- Because a leap day sits between them and the rest of the year. January’s doomsday is the 3rd in a common year and the 4th in a leap year; February’s is the last day of the month, the 28th or the 29th. Everything from March onward is unaffected, which is why the memorable pairs all start in April.
- Does this work for dates before 1752?
- The arithmetic does; the calendar may not. Britain and its colonies used the Julian calendar until September 1752 and then skipped eleven days to catch up, so a date recorded at the time and the same date read as Gregorian are different days. Catholic Europe made the jump in 1582 and Russia not until 1918, which is why old dates are often written with both.
- What day of the week was I born?
- Enter the date above and the answer comes with its working. Birth weekdays are close to evenly distributed, but not exactly: scheduled caesareans and induced deliveries have made weekday births noticeably more common than weekend ones in most developed countries over the last few decades.