Age calculator

What this calculator tells you

Your age is not one number. It is a count of completed years, then the completed months since your last birthday, then the days since your last monthly anniversary. That is why two people born in the same year can legitimately be different ages on the same day.

Alongside that, the calculator shows the same span in single units: total days lived, total weeks, and total hours. Those numbers are useful for forms, insurance questions, visa applications and anything that asks for an age in days.

How the calculation works

The method counts completed months first, then the days left over. In detail:

1. Count the months between the two dates: (end year − start year) × 12 + (end month − start month).
2. Add that many months to the date of birth, clamping the day to the last valid day of the target month. Someone born on 31 January reaches “one month later” on 28 February, not 3 March.
3. If that anchor lands after the target date, use one month less.
4. The remaining days are the difference between the anchor and the target date.
5. Whole years are the months divided by twelve.

This is the convention used on official forms: you have completed a month when the same day-of-month comes round again, or when the month is too short and its last day has passed. It is also why the answer can differ by a day or two from a calculator that just subtracts the three fields and borrows a flat 30 days.

A worked example

Take someone born on 15 June 1994, measured on 30 October 2026.

• Years: 2026 − 1994 = 32
• Months: October − June = 4
• Days: 30 − 15 = 15

No borrowing is needed, so the age is 32 years, 4 months and 15 days. Total days lived: 11,825. That is 1,689 weeks and 2 days, or 283,800 hours. The next birthday falls on 15 June 2027, 228 days after the measurement date.

Why the days field is the one people get wrong

Three things break simple subtraction:

• Month length. Months are 28 to 31 days. Borrowing a fixed 30 is wrong about a third of the time.
• Leap years. A 29 February birthday exists once every four years, and has to be handled explicitly rather than allowed to roll into March silently.
• Time zones and daylight saving. If you diff two timestamps instead of two calendar dates, a clock change can move the result by a day.

This page works in calendar dates and does all arithmetic in UTC, so none of those three cases can shift the answer. Invalid dates such as 31 February are rejected instead of being quietly converted to 3 March.

When you might need the exact form

Exact ages in years, months and days are asked for on medical forms, school admission cut-offs, some visa and pension applications, and in paediatric dosing. Where an official body defines age differently — for example, counting age as of 1 January — use their rule rather than this page.