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Age Calculator

Enter a date of birth to get an exact age broken down into years, months and days, along with the totals and the countdown to the next birthday. You can also set the second date to work out how old someone was, or will be, on any other day.

Defaults to today. Change it to work out an age on any date.

Enter a date of birth to calculate an exact age.

How to use this tool

  1. Enter the date of birth. The field uses your device's date picker, so the display format matches your own regional settings.
  2. Leave the second field on today's date for a current age, or change it to calculate an age on a specific past or future date.
  3. The exact age appears underneath, together with total months, weeks and days, and the days remaining until the next birthday.

Formula and method

Years, months and days

years  = end.year  − start.year
months = end.month − start.month
days   = end.day   − start.day

if days < 0:   borrow the length of the previous month
if months < 0: borrow 12 months from the year count

Age is counted the way a person would count it — calendar unit by calendar unit, borrowing from the next unit up when needed. Because months are different lengths, the borrowed number of days depends on which month is being borrowed from, which is why a fixed 30-day month gives the wrong answer.

Worked examples

Born 15 January 2000, age on 10 March 2024

  1. Years: 2024 − 2000 = 24
  2. Months: 3 − 1 = 2
  3. Days: 10 − 15 = −5, so borrow February's 29 days (2024 is a leap year) and reduce the months by one
  4. Days become 29 − 5 = 24, months become 1

24 years, 1 month and 24 days.

Born 29 February 2000 — when is the next birthday in 2025?

  1. 2025 is not a leap year, so 29 February does not exist
  2. The date falls back to the last day of the month

28 February 2025.

Notes and limitations

  • Dates are treated as calendar dates, not moments in time. The calculation ignores time of day and time zones entirely, so it gives the same answer wherever you are and is unaffected by daylight-saving changes.
  • Leap years are handled by the full Gregorian rule: divisible by four, except centuries, unless divisible by four hundred. The year 1900 was not a leap year; 2000 was.
  • A 29 February birthday is treated as falling on 28 February in common years, which is the most widely used convention. Some jurisdictions use 1 March for legal purposes.
  • Total months is the whole number of complete months, not the total days divided by an average month length. The two give different answers.
  • The default date comes from your own device clock. If your device's date is wrong, so is the result.

Frequently asked questions

How do I calculate my exact age?

Subtract the birth date from today one calendar unit at a time — years, then months, then days — borrowing from the next unit up when a figure comes out negative. Enter your date of birth above and the calculator does it for you.

How many days old am I?

The calculator shows the total number of days between your date of birth and today, including every leap day that has passed. It is listed under total days alongside the totals in months and weeks.

How is age calculated for someone born on 29 February?

In leap years the birthday falls on 29 February as normal. In common years this calculator treats it as 28 February, which is the usual convention. A few legal systems use 1 March instead, so check if it matters formally.

Can I calculate my age on a future date?

Yes. Change the second date to any future date and the calculator shows how old you will be then. It works for past dates too, which is useful for filling in forms that ask for your age at a particular time.

Why does total months not match total days divided by 30?

Because months are not 30 days long. Total months here counts complete calendar months, which is what people mean by the figure. Dividing days by 30 gives an approximation that drifts by several days a year.

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