Finding the weekday of a date
Want to know what day you were born on, or what day of the week a holiday falls on next year? Enter the date and the page shows the weekday at once, along with where the date falls in its year.
Examples
- January 1, 2000 was a Saturday, the first day of a leap year with 365 days still to come.
- October 17, 2026 is a Saturday, day 290 of the year, in ISO week 42.
- May 15, 1990 was a Tuesday.
Leap years
A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 2000 and 2024 were leap years, but 1900 was not and 2100 will not be. This is the rule of the Gregorian calendar, introduced in 1582.
Doing it in your head
Mathematician John Conway's "doomsday" method lets you find the weekday of any date mentally: certain easy-to-remember dates (4/4, 6/6, 8/8, 10/10, 12/12, and the last day of February) always fall on the same weekday in a given year. In 2026 that weekday is Saturday.
How this works
The page converts the date into a count of days in the Gregorian calendar and reads the weekday from it, writing the name in the page's language. It also counts the day of the year, finds the ISO 8601 week, checks the leap-year rule and subtracts the day of the year from the length of the year for the days left.
Frequently asked
What day of the week was I born?
Enter your date of birth and the page shows the weekday.
Is this year a leap year?
The page shows it for any date: years divisible by 4 are leap years, except centuries not divisible by 400.
Does it work for old dates?
Yes, using the Gregorian calendar extended backwards; before 1582 people used the Julian calendar.
What is the doomsday rule?
A mental method by John Conway that uses easy anchor dates that share a weekday each year.
Sources
Reviewed Oct 17, 2026 · test vectors fixtures/calculators/date/day-of-week-calculator/