What Day of the Week Was I Born

You need your full date of birth to find your birth weekday: the day, month and year. For example, 1 January 2000 was a Saturday, while 1 January 2001 was a Monday.

This is the weekday of the date you were born. Your birthday this year, or your next birthday, may fall on a different day of the week.

Weekdays repeat every seven days, but a year does not contain an exact number of weeks. A common year has 52 weeks and 1 day. A leap year has 52 weeks and 2 days.

Those extra days move the same date to a different weekday in the following year. Here is how 1 January changes:

The move from Saturday in 2000 to Monday in 2001 is two days because 29 February 2000 falls between those dates. For birthdays later in the year, check whether a leap day falls between the two birthdays. Simply knowing that one of the years is a leap year is not enough.

The calculation counts the days between your birth date and a date whose weekday is known. It then divides by seven and uses the remainder. Full weeks bring you back to the same weekday.

Starting with Saturday 1 January 2000, seven days later is Saturday 8 January. Ten days later is Tuesday 11 January: one full week takes you to Saturday, and three more days take you to Tuesday.

For dates farther apart, the count must include the actual month lengths and leap years. In the Gregorian calendar, a year divisible by four is usually a leap year. A century year also needs to be divisible by 400. That is why 2000 was a leap year and 2100 will not be. [S02]

It will not necessarily take seven years. Leap days change the pattern. Someone born on Saturday 1 January 2000 also had Saturday birthdays on 1 January 2005, 2011 and 2022.

The full Gregorian weekday pattern repeats over 400 years. That period contains 146,097 days, or exactly 20,871 weeks. Shorter repeats depend on the particular date and the leap years in between, so an “every seven years” shortcut is unreliable.

For your next celebration, the birthday countdown calculator shows the next birthday date and its weekday.

For a modern birth record, use the local date written on the record. Once you know that date, you do not need the birth time to find its weekday.

Time and location matter if you are converting the moment of birth to another time zone. A late-night birth in one place may fall on the next date elsewhere. The conversion can change the date, and therefore the weekday, you are asking about.

Historical records need a further check. This calculator uses the Gregorian calendar, extending it backward for earlier dates too. An old document may use another calendar. Establish which calendar the record uses before treating the result as the weekday observed in that place at the time.