Age Calculator
Calculate chronological age in years, months and days from a birth date, optionally at a chosen date — with totals in months, weeks and days, plus the next birthday.
Example values are shown — change any of them and the answer updates live.
| Next birthday | Jun 15, 2027 | in 271 days |
| Half-birthday | Dec 15, 2026 | in 89 days |
| 10,000th day | Oct 31, 2017 | 3,243 days ago |
| 20,000th day | Mar 18, 2045 | in 6,757 days |
How age is calculated
Age is calculated with the anniversary convention: you are one year older on each birthday (month and day of birth), not after 365 days. For months and days, the calendar borrows: your age in months is the number of full calendar months since birth — with each month clamped to its real length (31 January plus one month is 28 or 29 February, not 31 February) — and the remaining days complete the difference. This is why calendar age never drifts like a days ÷ 365.25 estimate.
Leap years and 29 February
Leap years add a 29th day to February. Years divisible by 4 are leap years, except century years unless they are divisible by 400: 2000 was a leap year, 1900 was not. For people born on 29 February, the birthday anniversary is observed on 28 February in non-leap years — the age still increments correctly every year.
Age in different units
The total-days count is exact: the number of 24-hour periods between two calendar dates (computed date-only, so time zones and clock time do not affect it). Weeks are whole weeks elapsed; hours, minutes and seconds are simple multiples of the exact day count. Months use the calendar count above, not days ÷ 30.44.
Worked examples
Example 1: born 15 June 1990, today 12 September 2026 → 36 years, 2 months, 28 days. Example 2: born 31 January 2026, on 28 February 2026 → exactly 1 month (the February anniversary completes early, clamped to 28 days). Example 3: born 29 February 2024, on 28 February 2025 → 1 year exactly.
Edge cases
A birth date in the future is rejected. A birth date equal to the reference date gives zero age. When the reference date is before the birthday in its year, the last year has not completed yet. All calculations are date-boundary based — a person is considered one day older at midnight of the next date, regardless of birth time.
Computed exactly from calendar dates (UTC) — no estimation involved.