Age Calculator

Age in years, months and days is calendar arithmetic, not division. The calculator steps forward from the date of birth one whole year at a time for as long as the result is still in the past, then one whole month at a time, then counts the days left over. That is why the answer reads the way a person says it out loud — thirty-four years, two months and nine days — rather than as a decimal nobody uses.

Months are not equal lengths, so the final day count depends on the month it lands in. Stepping forward one month from 31 January reaches 28 February in a common year and 29 February in a leap year, because there is no 31 February to land on. The calculator clamps to the last day of the shorter month, which is the convention civil registries and most legal definitions of age use, and it does the same in reverse so an age never jumps by a day between two adjacent inputs.

Total days lived is a plain count of days from one date to the other, and it includes every 29 February that fell in between. A year is a leap year when it divides by four, except centuries, except centuries that divide by four hundred: 2000 was a leap year and 1900 was not. The calculator applies that rule rather than assuming an average year length, so the total is exact rather than close, and the weeks figure is that same total divided by seven.

Someone born on 29 February has no birthday at all in a common year. This calculator treats 1 March as the day they turn a year older in those years, which is the more common civil convention, and it says which convention it used rather than leaving you to infer it from the number. The total days figure is the same either way, because it counts real days and not birthdays.

A date has no time zone until something gives it one. Both dates here are read as plain calendar dates and compared directly, so an age does not shift by a day because you opened the page on a flight or because a server sits in another country. The two dates are held in your browser and are not sent anywhere; nothing about a date of birth is stored, logged or transmitted.

By default the second date is today, taken from your device clock, and you can set it to any other date instead. That is what a form is asking for when it wants an age as at a particular day — a school cut-off, an insurance term, a visa application, a season that has not started yet. The next birthday line works the other way round: it names the date, the weekday it falls on and how many days are left. If you want the gap between two arbitrary dates rather than an age, the days between dates calculator does that, and the countdown timer counts to a moment in days, hours, minutes and seconds.