What this tool does
Age in decimal years is misleading: someone can be 30.99 and still be 30. This tool calculates age the way it is conventionally stated, as whole years, months and remaining days, and can also report the total days, weeks, and hours between two dates.
How it works
Calendar age is not a division. Months have different lengths, so the reliable method is to count complete years first, then complete months from the resulting date, then the remaining days. Doing it this way avoids the drift that appears when you average month length across a leap year.
Leap days are handled explicitly. Someone born on 29 February has an anniversary only in leap years, and the convention used here is that their age increments each year on the 28th outside a leap year, so their age is never a year behind.
The total-days figure uses the actual calendar and counts leap years across the whole span rather than approximating with 365.25. It measures the number of days that elapse from the start date to the end date, so two dates one day apart return 1.
Worked example
Age of someone born 14 March 1996, measured on 26 September 2026.
- 30 complete years (14 March 1996 to 14 March 2026)
- 6 complete months (14 March to 14 September 2026)
- Remaining days: 26 - 14 = 12
30 years, 6 months and 12 days.
Accuracy and limitations
- Uses the calendar date only. Where a specific time of day matters, such as for medical or legal deadlines, confirm against the relevant authority's rule.
- Public holidays and non-working days are not excluded from any day count.
Frequently asked questions
- How is age calculated exactly?
- By counting complete calendar units rather than dividing elapsed days by 365.25. Complete years are counted first, then complete months, then the leftover days. This matches how ages are stated on official documents and avoids drift caused by unequal month lengths.
- How are leap years handled?
- A year is a leap year if it divides by four, except centuries which must divide by 400. Days-between calculations count them accurately. For 29 February birthdays, age increments on the 28th in non-leap years so the person is never shown as a year younger.
- Can I find the date that someone turns a given age?
- Add the number of years to the birth date. If the resulting date does not exist, such as 29 February in a non-leap year, the convention here uses 28 February. This is useful for eligibility cut-offs and deadlines.
- Are the day counts inclusive?
- The total is the number of days that elapse between the two dates, not a count of both endpoints. Two dates one day apart give 1, and the same date twice gives 0. This is the convention used for most deadlines and countdowns.