How do you work out the day of the week?

The weekdays repeat every 7 days, so you can get any date's weekday from a date you already know. A normal year moves the weekday on by one, and a leap year by two: 1 January 2000 was a Saturday, so 1 January 2001 was a Monday.

For doing it in your head there's the doomsday rule. In any year, 4/4, 6/6, 8/8, 10/10, 12/12 and the last day of February all fall on the same weekday. In 2026 that's a Saturday, so 21 October 2026, eleven days after 10/10, is a Wednesday.

Tool description

Pick a Date, or press Today to jump back to the current one, and the tool shows:

  • Day of the Week, such as Wednesday
  • Full Date, written out in your language
  • Occurrence in Month, such as "3rd Wednesday of October", handy for things like "every second Tuesday"
  • ISO Day Number, from 1 for Monday to 7 for Sunday, as in ISO 8601
  • Day of Year, from 1 to 366
  • Weekday or Weekend, with Saturday and Sunday as the weekend

Everything is worked out in your browser. The tool uses the Gregorian calendar for every date, even before it was adopted in 1582, so very old dates won't match records kept in the Julian calendar.

Examples

Date Day Occurrence in Month ISO Day Number Day of Year
2000-01-01 Saturday 1st Saturday of January 6 1
1969-07-20 (Moon landing) Sunday 3rd Sunday of July 7 201
2024-02-29 Thursday 5th Thursday of February 4 60
2026-10-21 Wednesday 3rd Wednesday of October 3 294
2038-01-19 Tuesday 3rd Tuesday of January 2 19

Features

  • Finds the weekday of any date, past or future
  • Shows which occurrence of that weekday it is in the month
  • Gives the ISO day number and the day of the year