How to Calculate Age From a Date of Birth

Calculating age sounds simple, but exact results need care. Months have different lengths, leap years add an extra day, and many forms ask for age on a specific date rather than today. An age calculator handles these rules automatically.

The quick method

1. Subtract the birth year from the current year.
2. If the birthday has not happened yet this year, subtract one.

Example: born on 15 August 2000, checking on 21 October 2026 → 2026 − 2000 = 26, and the birthday has already passed, so the age is 26.

Exact age in years, months and days

1. Count full years since the date of birth.
2. Count full months since the last birthday.
3. Count the remaining days, borrowing the number of days in the previous month when needed.

Example: from 15 August 2000 to 21 October 2026 is 26 years, 2 months and 6 days.

What about leap-year birthdays?

People born on 29 February have a calendar birthday only every four years. Most systems treat 28 February or 1 March as the birthday in non-leap years, depending on local law. The calculator shows the exact elapsed time so you can apply the rule that fits your situation.

Use the free age calculator

1. Open the Age Calculator.
2. Enter the date of birth.
3. Optionally choose the date to calculate the age on (for example an exam or application deadline).
4. See the age in years, months and days, plus totals in months, weeks and days.

Related date tools

• Date Difference Calculator – days between any two dates.
• Date Calculator – add or subtract days, weeks, months or years.
• Business Days Calculator – working days between dates.