What day of the week was I born on?

Almost nobody remembers the weekday they were born on. Your parents might, or there’s a faded line on a birth certificate somewhere. Easier to just check:

How weekdays actually repeat

Weekdays run on a tight seven-day loop, so every date in history sits on a fixed day. The pattern shifts in a way that’s easy to picture once you see it.

A common year is 365 days. Divide by 7 and you get 52 weeks plus 1 leftover day. That single leftover is why your birthday lands one weekday later each year: a Tuesday birthday becomes a Wednesday the next year. For example, if you were born on a Friday, your birthday the following (common) year falls on a Saturday. The formal way to compute any date’s weekday is the Doomsday rule (source: Doomsday rule on Wikipedia). Then a leap year throws in 29 February, so the shift jumps by two instead of one whenever 29 February falls between two of your birthdays. (If you also want your age rather than the weekday, try the age calculator.)

So the sequence for a birthday isn’t random at all. It creeps forward by one most years, two across a leap day, and the whole thing cycles back around every 28 years (in the Gregorian calendar, ignoring the century quirks).

A quick sanity check

Some well-known dates make good reference points:

If the tool agrees with these, it’s working, and it does, because it uses the same date engine as the rest of the site.

Doing more with your birth date

The weekday is the fun fact. The age calculator goes further: exact age in years, months, and days, plus how that maps onto the Persian calendar. And if you were born on a Persian date and want its Gregorian twin (or the other way around), the Jalali ⇄ Gregorian converter handles that in a tap.

Worth knowing: the weekday is timezone-stable here. It’s computed from the calendar date itself, not your local clock, so two people checking the same birth date anywhere in the world get the same answer.