What day was it?
Enter any date, past or future, to find its day of the week. The calculator also gives the day of the year, the ISO week number, whether the year is a leap year, and how many days separate that date from today.
How it works
The calculator counts the days between the date and a reference date whose weekday is known, then takes the remainder of the division by 7. It uses the proleptic Gregorian calendar, the calendar in use today extended backward. Britain and its American colonies switched from the Julian calendar in September 1752, so for earlier English-language records, a date may be written in the old style and differ by 11 days or so.
Worked example
July 4, 1776, the date of the Declaration of Independence:
- The date is 91,432 days before November 3, 2026, a Tuesday.
- 91,432 = 7 × 13,061 + 5, so the weekday is 5 days before Tuesday.
- Result: Thursday. 1776 was a leap year, and July 4 was its 186th day.
The Doomsday rule
John Conway’s Doomsday rule lets you find the weekday of any date mentally. In each year, a set of easy-to-remember dates fall on the same weekday, the “doomsday”: 4/4, 6/6, 8/8, 10/10, 12/12, 5/9 and 9/5, 7/11 and 11/7, March 14 (Pi Day), July 4, Halloween, and the last day of February.
| Year | Doomsday |
|---|---|
| 2024 | Thursday |
| 2025 | Friday |
| 2026 | Saturday |
| 2027 | Sunday |
| 2028 | Tuesday (leap year) |
For 2026, doomsday is Saturday, so December 12 is a Saturday and December 25, 13 days later, is a Friday.
Leap years
A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. 2000 was a leap year, 1900 was not, and 2100 will not be. That rule keeps the calendar within about a day of the seasons over 3,000 years.
Fun uses
- Find the weekday you were born on, or of a parent’s or grandparent’s birth.
- Check the weekday of historic events, such as the Moon landing on Sunday, July 20, 1969.
- Plan future events: see whether a birthday or holiday falls on a weekend in a given year.