How old am I exactly? Age in years, months, and days

“How old are you?” gets a one-number answer. “How old are you exactly?” is a different question (years, months, and days), and it’s surprisingly easy to get wrong by hand because months aren’t the same length.

Enter your birth date and the tool sorts it out:

The method (and the borrowing trick)

Exact age is a subtraction with carrying, just like the arithmetic you learned as a kid, except the columns are days, months, and years, and they don’t carry in tens.

1. Subtract the day-of-month. If it goes negative, borrow a month and add that month’s length in days.
2. Subtract the month. If that goes negative, borrow a year and add 12 months.
3. Subtract the year.

The fiddly part is step 1: which month’s length do you borrow? It’s the previous month’s, and that varies: 28, 29, 30, or 31 days. Get that wrong and your “days” figure is off. This is the single most common mistake in age math, and it’s exactly the bit the age calculator gets right every time.

Why “just subtract the years” isn’t enough

Plenty of people compute age as this year − birth year. That’s fine until you hit the obvious problem: if your birthday hasn’t happened yet this year, you’re a year younger than that subtraction claims.

For example: born in November 2000, checking in July 2026? Year subtraction says 26. But your November birthday is still months away, so you’re actually 25 years and change. The exact method handles this automatically because the day and month comparison forces the borrow. No off-by-one. (This day/month/year breakdown is how ISO 8601 durations express ages too, source: ISO 8601 on Wikipedia.)

Two calendars, one age

Because this site runs on both calendars, the age tool can give your age counted in the Persian (Jalali) calendar too, useful if you think of your birthday in Shamsi terms. The total number of days is identical either way; only the years/months/days breakdown shifts, since the months have different lengths. There’s more on those lengths in the Persian months reference, and on the year-counting itself in how old am I in the Persian calendar.

If you just want to convert your birth date between calendars first, the Jalali ⇄ Gregorian converter does that, and the date difference calculator will count the raw days to any other date. Everything runs locally on your device.