How to Work Out the Day of the Week for Any Date

Finds which day of the week a date falls on, for any date in the Gregorian calendar, past or future.

Enter a year, a month and a day, and this tool gives the day of the week. It answers the weekday you were born on, the weekday of a historical event, or the weekday of an appointment far ahead.

w = ((n + 3) \bmod 7) + 1

Here $n$ is the day number of the date and $w$ the weekday, running from 1 for Monday to 7 for Sunday. Weekdays repeat every seven days and do nothing else, so the remainder on dividing the day number by seven is the whole answer. The 3 corrects for the reference date behind the day numbering, 1 January 1970, having been a Thursday.

Worked example

27 July 2026 is a Monday.

1 January 2026 was a Thursday, and 27 July is the 208th day of that year, so it lies 207 days later. Dividing 207 by seven leaves a remainder of 4, and four days on from Thursday is Monday.

Points to watch

The calculation follows the Gregorian calendar throughout. Countries adopted that calendar at different times, Britain in 1752 and Japan in 1873 among them, so for earlier dates the answer will not match the calendar then in local use.

The weekday is given by its English name, with the ISO 8601 number beside it so that nothing has to be looked up.