How to Use This Tool
Enter a date of birth and, if you want the age on some other date, change the second field. The answer uses the calendar method rather than dividing by an average year length.
Whole years, then whole months, then borrow
Age is counted in three steps, and every legal and administrative system agrees on them:
- Count complete years since the birth year.
- Count complete months since the last birthday.
- Count the days left over. If the day-of-month has not been reached yet, borrow the length of the preceding month.
Born 15 May 1990, measured on 11 August 2026: 36 complete years, then May to August is 3 months but the 11th is before the 15th, so only 2 are complete and the remaining days borrow July's 31 days, giving 27. The answer is 36 years, 2 months and 27 days.
That borrowing step is why the same gap in days can produce a different month-and-day result depending on where in the year it falls — borrowing February's 28 days is not the same as borrowing July's 31.
Why dividing by 365.25 gives a different number
The same example is 13,237 days. Divide by 365.25 and you get 36.2409 years; divide by 365 and you get 36.2658. Neither is the calendar answer, and neither is stable — the error moves depending on how many leap years happen to fall inside the interval.
For a rough figure it does not matter. For anything where a threshold applies — a pension date, a minimum age, a school year cut-off — use the calendar method, because that is what the rule means.
The leap-day birthday
If you were born on 29 February, three quarters of your birthdays do not exist. Under the borrowing convention above, on 28 February 2026 you are 25 years, 11 months and 30 days — and you turn 26 on 1 March.
That is a convention, not a fact about the world. Some jurisdictions define the anniversary as 28 February for legal purposes, which matters for things like coming of age or a licence expiring. If the date is load-bearing, check the specific rule; if it is a birthday party, pick whichever you prefer.
Time zones can move the answer by a day
Age is a date calculation, not a timestamp calculation, so this tool treats both dates as plain calendar dates with no time zone attached. That is deliberate: if it used your local clock, someone born in Auckland and measured in Los Angeles could come out a day younger than the passport says. Every official calculation uses the calendar date as written on the document.
