Age calculator

Why “as of” is a field and not just today

This site builds to static files, so the page you’re reading was written before you opened it and has no way of knowing what day it is. A page that said “today” would be right on the day it was published and quietly wrong every day after. Instead the reference date is stated, so the answer is true for the date it names — and if your browser runs JavaScript, it’s already been moved to your actual today.

It’s also useful on its own: ages are usually wanted as of a specific date — a school cutoff, a policy start, a date in the past — rather than as of right now.

Leap-day birthdays

Someone born on 29 February turns a year older on 28 February in a common year here. That follows from how this site adds months and years everywhere else: a day that doesn’t exist in the target month clamps to the last one that does. Holding the anniversary to 1 March instead would mean adding a year and measuring a year gave different answers, and a calculator that disagrees with itself is worse than one that picks a convention and says so.