Age Calculator

How the age calculation works

Your age is not simply the number of days since you were born divided by 365. Months have between 28 and 31 days, and every fourth year (with a few exceptions) has an extra day. To give an answer that matches how people actually talk about age, the calculator works in three steps:

1. Full months. It counts how many whole months fit between your date of birth and the target date. A month is complete when the same day number comes around again — from May 15 to June 15, for example.
2. Years and months. Those whole months are split into years (12 months each) and the months left over.
3. Remaining days. Finally it counts the days from the last “monthly anniversary” to the target date.

So someone born on May 15, 1990 is 36 years, 4 months and 25 days old on October 10, 2026: 436 whole months have passed (36 years and 4 months), the last monthly anniversary was September 15, 2026, and 25 days have passed since then.

End-of-month birthdays

If you were born on the 31st, some months simply don’t have that day. In that case the monthly anniversary falls on the last day of the shorter month. Born on January 31? Your first “month” is complete on February 28 (or the 29th in a leap year). This is the same rule that banks and most calendar software use when they add months to a date.

Leap years and February 29

A year is a leap year when it is divisible by 4, except for years divisible by 100 that are not divisible by 400. That is why 2000 was a leap year but 1900 was not. People born on February 29 — sometimes called leaplings — celebrate their real birthday only once every four years. In the years between, this calculator moves the birthday to February 28, so the age changes on the last day of February rather than skipping into March.

What the totals mean

• Total months is the number of complete months you have lived.
• Total weeks is the number of complete weeks; the remaining days are not shown.
• Total days counts every calendar day from your date of birth up to the target date, including leap days.
• Total hours multiplies the total days by 24.

Common uses

People use an age calculator to fill in forms that ask for age in years and months (sometimes called chronological age), to check eligibility for school entry, sports categories, pensions or insurance, to work out a baby’s age in months or weeks from the totals above, or simply to count down to the next birthday. Because you can change the second date, it is also a quick way to find out how old a historical figure was at a certain event.

This tool always counts from a date of birth. To count the days between any other two dates, such as the days left until a trip or the business days in a project, use the date calculator instead.