Date & Time · 1 min read
How to calculate age from a date of birth
Age in whole years is a subtraction with one check. Exact age in years, months and days needs a little more care.
Last updated November 3, 2026
Age in whole years
Subtract the birth year from the current year. If this year's birthday has not happened yet, subtract one more.
Age in years, months and days
Count full years from the birth date to the most recent birthday, then full months from that birthday, then the remaining days.
Born 14 May 2000, on 30 September 2026
| Part | Span | Result |
|---|---|---|
| Full years | 14 May 2000 to 14 May 2026 | 26 years |
| Full months | 14 May to 14 September | 4 months |
| Days | 14 to 30 September | 16 days |
Result: 26 years, 4 months and 16 days
When the day number is smaller
If the current day of the month is earlier than the birth day, borrow a month and add the number of days in the previous month. This is why two tools can differ by a day or two when they borrow differently: the length of the month used matters.
Leap-day birthdays
A person born on 29 February has a birthday only in leap years. Many places treat 28 February or 1 March as the birthday in other years.
Important
Legal rules differ, so check the rule that applies to you if the exact date matters.