CalculatorsConvertersDeveloperTextAll toolsDirectory
Submit your tool Sign in
Theme
Home/Answers/Calculators
How-to

How do I calculate age from a date of birth?

Short answer

Subtract the birth year from the current year, then subtract one more if the birthday has not happened yet this year. Someone born on 15 August 1990 is still 35 on 14 August 2026 and turns 36 on 15 August 2026. A free age calculator does this instantly and also gives the exact age in months and days.

The birthday rule

Year subtraction alone overstates age for part of the year. The correct method is: current year minus birth year, minus one if the current date is before the birthday. That single adjustment is what forms, banks and airlines mean by age, and it is the step people forget when they do it in their head.

Age in days, months and other fun units

Because a calendar year averages 365.25 days once leap years are included, 10,000 days works out to about 27.4 years. An age calculator that reports years, months and days handles leap years and different month lengths exactly, which is fiddly to do by hand and instant in the browser.

Frequently asked questions

How does age work for someone born on 29 February?

In common years there is no 29 February, so the birthday is usually observed on 28 February or 1 March. An exact age calculator still counts the days precisely.

How many years is 10,000 days?

About 27.4 years, since an average year is 365.25 days once leap years are counted.

Why subtract one from the year difference?

Because until the birthday arrives, the person has not completed that year of life yet. Born August 1990 means still 35 in July 2026, not 36.

Related answers