Age looks like "this year minus birth year," but your true age depends on whether your birthday has passed yet. This guide explains how age is correctly calculated and how to express it in years, months and days. To see your own age down to the day, use the age calculator.
How is age calculated?
The correct method is to subtract the birth date from today's date. You take the difference in years — but if this year's birthday hasn't happened yet, you subtract one year. For example, someone born in December 2000 is 25, not 26, in August 2026, because the December birthday hasn't arrived.
In years, months and days
A full age is often written as "X years, Y months, Z days." To find it, you count the years first, then the remaining months, then the leftover days. Because month lengths vary from 28 to 31 days, doing this breakdown by hand can mislead; a tool handles the month and day rollovers correctly.
Leap years and 29 February
For people born on 29 February, age still increases every year; in non-leap years the birthday is usually treated as 28 February or 1 March. The calculator accounts for this special case.
How many days or months old?
You may want your age as total days, weeks or months instead of years — "how many months" for babies, or "how many days have I lived" as a fun fact. The age calculator shows all of these at once. To measure any two dates in general, you can also use date difference.
In short
Age is found by subtracting the birth date from today; if this year's birthday hasn't happened, subtract one year. A full age is expressed in years-months-days, and leap years affect the count. To see your exact age in seconds, try the age calculator.