How to use the day of the week calculator
Pick any date from 1 January 1583 to 31 December 9999. The result shows straight away:
- the weekday, in a sentence such as “25 December 2026 is a Friday” or “20 July 1969 was a Sunday”;
- the day of the year, from 1 to 365, or 366 in a leap year;
- the ISO week number, the week numbering used in Europe and in business planning (see week numbers);
- whether the year is a leap year;
- the next year in which the same date falls on the same weekday.
Below the result, a step-by-step table works out the weekday with John Conway’s Doomsday rule, so you can check the answer or learn to do it without a calculator. The Doomsday calculator page explains each step in detail.
Example dates
| Date | Weekday | Note |
|---|---|---|
| 4 July 1776 | Thursday | US Declaration of Independence |
| 1 January 1900 | Monday | 1900 was not a leap year |
| 20 July 1969 | Sunday | Apollo 11 Moon landing |
| 9 November 1989 | Thursday | Fall of the Berlin Wall |
| 1 January 2000 | Saturday | 2000 was a leap year |
| 25 December 2026 | Friday | Day 359, ISO week 52; next Friday Christmas in 2037 |
How the weekday is calculated
A week has seven days, so the weekday of a date depends on how many days have passed since a known starting point, divided by seven. A common year has 365 days, which is 52 weeks and 1 day, so a date moves one weekday later each year. A leap year has 366 days, so dates after February 29 move two weekdays.
The Gregorian calendar has three leap year rules:
- A year divisible by 4 is a leap year,
- except a year divisible by 100, which is not,
- except a year divisible by 400, which is a leap year after all.
So 2000 was a leap year, but 1900 was not and 2100 will not be. These rules make the calendar repeat exactly every 400 years, because 400 Gregorian years contain exactly 20,871 weeks. That is why a weekday can be calculated for any date in the range. See what is a leap year for the full story.
Calendar reform
The Gregorian calendar replaced the Julian calendar in 1582, when ten days were dropped. Not every country switched then: Great Britain and its colonies changed in 1752, and other countries later still. The calculator always uses the Gregorian calendar, so for historical dates check which calendar the source used. To count the days between two dates, use the days between dates calculator, or browse a full 2026 calendar.