Age Calculator

Details

About this tool

Turns a birth date into an exact age on any date you choose, plus the total in months, weeks, days and hours, the weekday you were born on, and the countdown to the next birthday.

Age sounds like subtraction and is not. Calendar months have different lengths and leap years add a day, so an age is counted the way people count it: whole years first, then whole months from the last birthday, then the days left over. Dividing the total days by 365 gives a different - and wrong - answer, drifting by a day for roughly every four years lived.

That distinction matters wherever an age is a legal fact rather than a nicety: eligibility thresholds, insurance bands, pension dates, retirement calculations, medical dosing by age, school enrolment cut-offs. In all of them the boundary falls on a birthday, not on a count of days, and "how old on this specific date" is the question actually being asked - which is why the second date is adjustable rather than fixed to today.

Someone born on 29 February has a birthday in three years out of four. The convention here is that in a common year the birthday falls on 1 March, which is what most legal systems use, though a few treat 28 February as the date instead - worth checking if the day itself carries a consequence.

The calculation is calendar arithmetic on day numbers with no time zone involved, so it cannot shift by a day depending on where you are, and it runs entirely in your browser: a date of birth is personal data and there is no reason for it to leave your device.

Good to know

Questions people actually ask

How is someone born on 29 February aged?

Their birthday falls on 1 March in a common year, which is the convention most legal systems follow. A minority treat 28 February as the date instead. It only matters when the day itself carries a consequence - a threshold, a policy start - and in that case check the rule that applies to you.

Why not just divide the days by 365?

Because that ignores leap years and drifts by about a day every four years. Someone who has lived 7305 days is 20 years old exactly, but 7305 ÷ 365 gives 20.01. Age is counted in whole years from the birthday, then whole months, then the remaining days - which is what this does.

Can I work out an age on a past or future date?

Yes - the second date is adjustable rather than fixed to today. That is the question that usually needs answering: how old someone was on the date of an event, or will be when a policy starts or a threshold is reached.

Is a birth date sent anywhere?

No. All the arithmetic happens in your browser. A date of birth is personal data, and there is no reason for a calculator to have it on a server.

Why does the result differ from another calculator by a day?

Almost always a time zone. Tools that build a timestamp from a date and then convert it can shift the day depending on where the visitor is. This one works on calendar day numbers with no time of day involved, so the answer is the same everywhere.