Birthday Calculator

Enter your birth date and the calculator shows the weekday instantly. Fun fact: calendars repeat on a mostly 28-year cycle — the weekdays of a given year match again 28 years later about 3 times in 4, drifting only when the span crosses a century year like 2100 that is not a leap year.

Each person has about a 1 in 365 chance of sharing your exact birthday (1 in 1,461 for February 29). In a group of 23 people there is already a 50.7% chance that some two members share a birthday — the famous birthday paradox — and with 75 people it exceeds 99.9%.

Your half birthday falls about six months after your birthday — add roughly 182 or 183 days, depending on the months involved. People with December birthdays sometimes celebrate half birthdays in June so outdoor parties avoid winter; schools also use half birthdays for summer-born kids so no one misses a classroom celebration.

A calendar year is 365 days, or 366 in a leap year because February 29 adds one day. If your birthday is before February 29 in a leap year, your countdown includes that extra day. The tool always counts across real calendar dates, so the number it shows is exact for the current year.

It shows the weekday you were born, total days lived, your next birthday date and countdown, your zodiac sign and Chinese zodiac animal, plus birthstone and birth flower for your month. Everything is computed locally in your browser — your birth date is never sent to a server.