How do I calculate an exact age?

Subtract year from year, month from month and day from day, borrowing where a subtraction goes negative. Dividing total days by 365.25 is an approximation that drifts around birthdays.

What happens with a 29 February birthday?

In non-leap years this calculator uses 1 March as the birthday, which matches the most common legal convention. Some jurisdictions use 28 February instead.

Age Calculator

Work out an exact age in years, months and days from a birthdate, plus days until the next birthday.

Draft — figures checked, awaiting an editorial read. Not indexed.

Years— years

Months: — months
Days: — days
Total days lived: — days
Total weeks: — weeks
Days to next birthday: — days
Note: —

Formula: Subtract the birthdate from the target date field by field, borrowing days from the preceding month and months from the year where needed.

What this calculates

This gives an exact age in years, months and days as of today or any date you choose, along with the total days lived and the countdown to the next birthday. Calculating age properly is harder than subtracting two years, because months have different lengths and leap years exist. Dividing total days by 365.25 gets close but drifts, and the drift is largest exactly where precision matters most — around a birthday, and for young children where months are the meaningful unit.

How it works

The two dates are subtracted field by field: years from years, months from months, days from days. Where the day of the target date falls before the day of birth, a month is borrowed and the days of the preceding month are added — which is why the answer depends on the actual calendar rather than an average month length. Where the month then goes negative, a year is borrowed. All arithmetic runs in UTC so daylight saving transitions cannot shift a date across a boundary.

Worked example

Someone born 15 June 1990, as of 21 August 2026. Years: 2026 − 1990 = 36. Months: 8 − 6 = 2. Days: 21 − 15 = 6. No borrowing is needed, so the answer is 36 years, 2 months and 6 days. Had the target date been 10 August instead, the day subtraction would go negative — 10 − 15 = −5 — so a month is borrowed, July's 31 days are added to give 26 days, and the months drop to 1.

Common mistakes

Dividing total days by 365.25. It is a reasonable approximation and it is wrong by a day or two either side of a birthday, which is the one time anyone checks. Second, mishandling 29 February birthdays — this calculator treats the next birthday in a non-leap year as 1 March, which is the common legal convention, though jurisdictions vary. Third, forgetting time zones: an age is a date calculation, and running it in local time near midnight can shift the answer by a day.

Common questions

How do I calculate an exact age?: Subtract year from year, month from month and day from day, borrowing where a subtraction goes negative. Dividing total days by 365.25 is an approximation that drifts around birthdays.
What happens with a 29 February birthday?: In non-leap years this calculator uses 1 March as the birthday, which matches the most common legal convention. Some jurisdictions use 28 February instead.