Age Calculator

How to use the Age Calculator

1. 1
   Enter the date of birth. Use the year-month-day picker. Any date is accepted, including leap days.
2. 2
   Set the date to measure against. It defaults to when this page was updated. Change it to today, or to a future date.
3. 3
   Read the breakdown. Exact age, total days and weeks lived, the weekday of birth, and days until the next birthday.

About calculating age

Age looks trivial until you try to compute it precisely, at which point the calendar stops cooperating. Months are not a fixed length, so "one month after 31 January" has no obvious answer — 31 February does not exist. The convention used here, and by most date libraries, is to clamp to the end of the target month, making it 28 February. That single decision resolves a surprising number of edge cases, including leap-day birthdays. A related trap is subtracting date components independently: taking 1 March minus 31 January gives one month and minus two days, which is nonsense but is exactly what a naive implementation produces. This calculator instead advances whole months from the birth date without overshooting, then counts the remaining days, which cannot go negative. It also reports total days lived, which is the figure to use for anything that needs arithmetic rather than presentation, since it carries no month-length ambiguity at all. Everything runs in your browser and in UTC, so the answer does not drift with your timezone or reach a server.

Frequently asked questions