Day of the Week Calculator

How the Day of the Week Calculator works

How the day of the week calculator works

The weekday cycle has repeated every seven days without a break since the Gregorian calendar began, so the formula counts the days between a known date and yours and takes the remainder after dividing by seven. A remainder of zero gives the same weekday as the reference date, one gives the next weekday, and so on.

Worked examples

For example, the Moon landing on 20 July 1969 was a Sunday: it was the third Sunday of July and day 201 of the year. As a second example, 1 January 2000 was a Saturday, and the United States Declaration of Independence, 4 July 1776, was signed on a Thursday. Enter any of those dates to check.

Why the weekday shifts each year

A common year of 365 days is 52 weeks and one day, so a date moves forward one weekday each year. After 29 February in a leap year it moves two. That is why your birthday usually falls a day later each year, and sometimes jumps by two.

How many days until the weekday repeats?

A calendar for one year can be reused when the next year starts on the same weekday and has the same length. That happens after 6, 11 or 28 years, depending on where the year sits in the leap cycle.

Day of the week for 1 January and 25 December, 2020 to 2043

Related tools