How do you calculate age in years, months and days?

Count whole years first, then whole months, then the days left over. The calculator does it by finding the largest number of whole months between the two dates and measuring the remainder in days from there, which avoids the negative day counts that simpler methods produce around short months.

What happens if I was born on 29 February?

Your exact age in years, months and days is still precise, because it is measured from the real date. For the next birthday countdown in a year with no 29 February, the calculator uses 28 February and says on screen that it has done so. Different countries and institutions handle this differently, so check what your own paperwork says if it matters legally.

Why do some age calculators disagree with each other by a day?

Almost always because of how they borrow days across a month boundary. From 31 January to 1 March, one method says one month and one day and another says one month and minus one day, which then gets patched into something wrong. This page adds months with the day clamped to the length of the month it lands in, so 31 January plus one month is 28 or 29 February and the remainder is never negative.

Can I work out age on a date other than today?

Yes. Switch the second date away from today and put in any date you like. That is how you check an age on an application cut-off date or an exam eligibility date rather than on the day you happen to be looking.

Is the age calculator free?

Yes. It runs entirely in your browser, there is no account and no signup, and neither date you type is sent anywhere.

Age calculator

Your exact age in years, months and days, on today or on any date you choose. It also gives the total in days and weeks and counts down to your next birthday. Leap years and short months are handled properly, which is where most age calculators quietly go wrong. Free, no signup.

Date of birth

Age on

Pick another date to check an age on an application cut-off or an exam eligibility date.

Pick a date of birth and a date to measure to.

How age in years, months and days is worked out

Age looks like simple subtraction and is not. Taking one date away from another field by field gives you a day count that can come out negative, and the usual fix is to borrow days from a neighbouring month. Which neighbouring month you borrow from is exactly where different calculators disagree, and it is why two of them can be a day apart on the same pair of dates.

This page avoids the borrow entirely. It counts whole months first, then measures what is left in plain days:

months = largest n where birth date + n months is on or before the target date

years = floor(months / 12), remaining months = months mod 12

days = calendar days from (birth date + months) to the target date

Adding a month clamps the day to the length of the month it lands in, so 31 January plus one month is 28 February, or 29 February in a leap year. Because the anchor date is always on or before the target, the leftover day count can never be negative and never needs patching.

Leap years, and the case that breaks other calculators

A year is a leap year when it divides by 4, except that a century year has to divide by 400. So 2000 and 2024 have a 29 February, and 1900 and 2100 do not. The total day count on this page is a real calendar count, so every leap day between your two dates is included.

31 January to 1 March. In a leap year the answer is 1 month and 1 day, because 31 January plus one month is 29 February, and 1 March is one day after that. A calculator that borrows the length of the month before the target date instead ends up with 1 month and minus 1 day and then rounds its way to something wrong.

Born on 29 February. From 29 February 2000 to 28 February 2001 this page reports exactly 1 year, and 365 days. From 29 February 2004 to 29 February 2024 it reports exactly 20 years, and 7,305 days, which is 20 times 365 plus the 5 leap days in between.

For the birthday countdown in a year with no 29 February, the page uses 28 February and says so on screen. That is a convention rather than a fact of arithmetic, and countries differ on it, so check your own paperwork wherever it matters legally.

A worked example

Take a birth date of 15 August 1995 and a target date of 15 August 2025. The exact age is 30 years, 0 months and 0 days. The total is 10,958 days, not 10,950, because 8 leap days fall in that span: 1996, 2000, 2004, 2008, 2012, 2016, 2020 and 2024. In whole weeks that is 1,565 weeks and 3 days.

Move the target date back one day to 14 August 2025 and the age becomes 29 years, 11 months and 30 days, with 1 day left until the birthday. The jump from 29 years and 11 months to 30 years happens on the day itself, which is the behaviour every eligibility form assumes.

Frequently asked questions

How do you calculate age in years, months and days?: Count whole years first, then whole months, then the days left over. The calculator does it by finding the largest number of whole months between the two dates and measuring the remainder in days from there, which avoids the negative day counts that simpler methods produce around short months.
How does this handle leap years?: February is treated as 29 days in a year divisible by 4, except centuries that are not divisible by 400. So 2000 and 2024 have a 29 February and 1900 and 2100 do not. The total day count is a real calendar day count, so every leap day between the two dates is included.
What happens if I was born on 29 February?: Your exact age in years, months and days is still precise, because it is measured from the real date. For the next birthday countdown in a year with no 29 February, the calculator uses 28 February and says on screen that it has done so. Different countries and institutions handle this differently, so check what your own paperwork says if it matters legally.
Why do some age calculators disagree with each other by a day?: Almost always because of how they borrow days across a month boundary. From 31 January to 1 March, one method says one month and one day and another says one month and minus one day, which then gets patched into something wrong. This page adds months with the day clamped to the length of the month it lands in, so 31 January plus one month is 28 or 29 February and the remainder is never negative.
Can I work out age on a date other than today?: Yes. Switch the second date away from today and put in any date you like. That is how you check an age on an application cut-off date or an exam eligibility date rather than on the day you happen to be looking.
Is the age calculator free?: Yes. It runs entirely in your browser, there is no account and no signup, and neither date you type is sent anywhere.

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