Exact age in years, months and days plus next-birthday countdown.
Updated
Quick start
Pick a date of birth (and optionally a reference date — defaults to today) and read the exact calendar age plus useful totals.
Set the date of birth. The reference date defaults to today, but you can change it to any date.
See calendar age in years, months and days, plus total months, weeks, days, hours, minutes and seconds.
Find out how many days until the next birthday, what weekday it falls on, and the next round-number milestones (10 000 days, 1 billion seconds, etc.).
In-depth guide
"How old am I?" sounds like a one-line answer, but the right way to compute it requires walking the calendar day by day. This guide explains how this tool figures it out, the edge cases (leap days, end-of-month birthdays), and a few related metrics worth knowing.
It's tempting to write:
age = currentYear − birthYearBut this overstates age by 1 for anyone whose birthday hasn't happened yet this year. Born in December 1990? In January 2024 you're still 33, not 34. Subtracting years also breaks completely when you cross month and day boundaries — try working out the age of someone born on a leap day if you want to feel the pain.
This tool walks the calendar the same way you would on paper:
The result is a triple (Y, M, D) that satisfies D < days-in-prev-month and M < 12 — exactly what a human would say.
About 1 in 1 461 people are born on Feb 29 (≈ 5 million worldwide). Their birthday only exists in years divisible by 4 (with the usual Gregorian carve-outs for centuries). This tool handles it the standard way:
End-of-month birthdays follow the same logic: someone born on Jan 31 still "turns" on Jan 31 every year, regardless of February's length.
Below the exact age, this tool shows a handful of raw totals — how many seconds, minutes, hours, days, weeks and months have passed since the date of birth. They're satisfying in a useless-fact way ("I've been alive for over 1 billion seconds!") and occasionally useful for trivia, milestone planning or just calibrating intuition.
The milestones table picks out the closest round-number anchors: every 10 000 days, half a billion seconds, the next "big" birthday. Past and future are listed together, ranked by how close they are to the reference date.
No. Age math runs entirely in your browser. Nothing is sent to a server, stored or logged.
We compute calendar age by stepping years/months/days separately and borrowing across months when needed, exactly like a human would: subtract the day, borrow from the month if it went negative, subtract the month, borrow from the year. That way February is 28 (or 29) days, and a leap-day birthday lands on Feb 29 in leap years and Mar 1 the rest of the time.
In non-leap years, the next-birthday countdown lands on Mar 1 because Feb 29 doesn't exist. The exact-age value is unaffected — you still gain a year on Feb 29 / Mar 1 depending on which one the calendar offers.
Total months is years × 12 plus the residual months — i.e. how many full calendar months have elapsed. It doesn't include the dangling days. The total days figure is the more accurate raw count.
By default it's today, so you get the live age. But you can set it to any date — useful for working out how old someone will be on a specific event, or how old a historical figure was at a specific moment.
Standard nerd-fun anchors: every 10 000 days lived, the half-billion-second mark, the billion-second mark, and a few legal-age birthdays (18, 21, 30, 50, 65, 100). The list is sorted by how close it is to your reference date.
Calendar age is not just (current year − birth year). Someone born in December 1990 is still 33 in January 2024, not 34, because their birthday hasn't come yet. Subtracting years overstates age by 1 for anyone whose birthday is later in the year.
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