Compute exact age in years, months, and days between a birth date and a reference date using calendar arithmetic—the same breakdown used on legal forms, eligibility checks, and milestone reminders.
Algorithm
Starting from the reference date, subtract the birth year, month, and day. If the day difference is negative, borrow one month and add the length of the previous calendar month (28–31 days). If the month difference is negative, borrow one year and add 12 months. The result is three non-negative integers: years, months, and days.
Dates are parsed as ISO YYYY-MM-DD strings in local time. When no reference date is supplied, today is used automatically.
When to use it
Handy for verifying age on a specific deadline (school enrollment, contract start, insurance effective date), calculating tenure or membership duration, or teaching calendar borrowing without a spreadsheet.
Limitations
Invalid date strings and reference dates before the birth date return explicit errors instead of partial results. Leap days are handled by native date logic, but timezone boundaries at midnight are not modeled—use noon UTC dates if you need cross-timezone consistency. The tool counts calendar units, not total elapsed days or hours.
Example
Birth 2000-01-01 with reference 2024-06-15 yields 24 years, 5 months, 14 days.