Age Calculator

Subtracting two calendar dates sounds simple, but doing it correctly means accounting for months of different lengths (28 to 31 days), leap years (an extra day every 4 years, with exceptions for century years), and the fact that "how many months" depends on which specific months you're counting between. A naive calculation — just subtracting year, month, and day components independently — produces wrong results whenever the day-of-month or month components don't line up cleanly, which is most of the time.

This calculator handles that correctly: it walks from your date of birth forward to the reference date, borrowing days from the previous month and months from the previous year exactly the way you'd count by hand, so the years/months/days breakdown is always exact — not an approximation based on average month length.

Checking eligibility for something with an exact age cutoff (school admission, a competition, a legal age requirement), filling in an exact age on a form instead of just a birth year, figuring out how many days old a baby is, or simply settling an argument about exactly how many days until a birthday. Because you can set the reference date to anything — not just today — it also works for calculating someone's age as of a past or future date, like how old someone was on a specific historical date, or will be on a future one.