🎂 Age Calculator
Exact age in years, months, and days. Runs privately in your browser.
Why calendar age is fiddlier than it looks
Calendar arithmetic is fussier than it looks: months have different lengths, and a person born on the 31st has no '31st' in every month. The calculator counts whole years first, then whole months, then leftover days — the same convention used on official documents — and it uses your browser's local timezone so there are no off-by-one surprises around midnight.
The 'as of' field defaults to today but accepts any date. That turns the tool into a countdown ('how old will I be at the 2030 deadline?') or a historical check ('how old was she when the treaty was signed?'). Age on a future date shows the age you will have reached on that date.
How the years, months and days are counted
Age = full years between dates + remaining whole months + remaining days, borrowing from the actual length of the previous month when the day-of-month goes negative — exactly how calendars, not averages, count time.
Worked through: born 15 March 1990
Born 15 March 1990, as of 9 September 2026: 36 years, 5 months, 25 days. If the as-of date is 15 March 2027, the result is exactly 37 years, 0 months, 0 days. A baby born 31 January has no '31 February' problem: the calculator rolls correctly to the end of shorter months.
Where people slip up
- Confusing the date of birth format expectations — the input uses your browser's date picker, which follows your locale.
- Expecting age in total days only — use the Date Difference Calculator for raw day counts.
- Forgetting timezone: a birth at 23:30 on the 14th is legally the 14th, not the 15th.
- Leap-year birthdays are counted on 28 Feb or 1 Mar by convention — the calculator follows standard legal counting.
Age questions we get asked
Why does my age differ by a day from another website?
Timezones. Many sites compute in UTC; this one uses your browser's local time, matching your documents.
Can I calculate age at a future date?
Yes — set the 'as of' field to any future date to see the age that will have been reached.
Does it handle leap years?
Correctly — 29 February birthdays and leap-year spans are counted per the calendar.
How do I get just the total days?
The Date Difference Calculator between birth date and target date gives raw days directly.
Is this how official age is calculated?
Yes — the year/month/day borrowing convention matches what government and medical forms expect.
Other date tools
Tip: double-check inputs before relying on results for important decisions.