Day of the Week Calculator

Find the weekday of any date

Wondering what day of the week you were born, when a historic event happened or what weekday a future date lands on? Pick a date and this calculator tells you instantly. It shows the weekday in large type, the full date in your language, the day number within the year, the ISO week number and how many days the date is from today.

For example, 12 March 1987 was a Thursday. The calculator uses the proleptic Gregorian calendar, which means the modern calendar rules are applied to every year, including dates before the calendar was adopted in 1582.

How weekdays are determined

Calendar days repeat in a seven-day cycle, so a weekday can be calculated from the total number of days since a known reference date. The rules for leap years add an extra day in February and shift weekdays in later years. Instead of using a formula by hand, the tool relies on the browser's built-in date engine, which handles leap years and century rules correctly.

If you are working with dates before 1582 and need the Julian calendar, see the calendar converter on this site, since Julian and Gregorian dates differ by several days.

Useful applications

People use weekday lookups for birthday and anniversary trivia, genealogy research, planning events years ahead, checking contract deadlines, and settling friendly arguments. The distance from today is shown as days ago or days from now, so you can see how long ago something happened. All calculation takes place in your browser; the date you enter is never sent to a server.

A neat curiosity is that the calendar repeats every 28 years in the Gregorian system, except across century years that are not leap years. That is why a date can fall on the same weekday as it did many years earlier, which you can test with this tool.