Age Calculator

How the age calculator works

Enter a date of birth and the date you want to measure to, which defaults to today. The calculator counts complete years first, then the complete months left over, then the remaining days. If the day of the month hasn't been reached yet, it borrows the number of days in the previous month, the same way you'd figure age by hand. It also shows the total number of days and weeks between the two dates.

Why age math is tricky

Months have 28, 29, 30 or 31 days, and leap years add February 29 every four years (except century years not divisible by 400). That makes "how many months and days old" less simple than dividing by 30. For example, from January 31 to March 1 is one month and one day in a non-leap year when counting from the end of February. This calculator uses actual calendar dates so leap years and month lengths are handled correctly.

Common uses

• Checking eligibility for school enrollment, sports leagues, retirement benefits or age-restricted services.
• Filling out forms that ask for age in years and months.
• Finding a baby's age in weeks or months.
• Calculating the age of a pet, building, or anniversary.
• Planning milestone birthdays such as 10,000 days old.

Leap-day birthdays

People born on February 29 celebrate on February 28 or March 1 in common years, depending on custom or local law. This calculator considers the birthday reached once the calendar date passes February 28 in non-leap years.

Age in other cultures

Some East Asian traditions count a newborn as one year old and add a year at the new year. This calculator uses the international standard: age 0 at birth, one year added on each birthday.