Age in Years

Age = Reference Date − Birth Date (accounting for whether birthday has passed)

Calculates completed years by comparing the birth date to the reference date, adjusting for whether the birthday has occurred yet in the current year.

Age in Months

Total Months = (Years × 12) + Remaining Months

Converts the age into total calendar months by multiplying completed years by 12 and adding any additional months since the last birthday anniversary.

Age in Days

Total Days = Reference Date − Birth Date (in days)

Counts every calendar day between the birth date and the reference date, automatically accounting for leap years (366-day years) and varying month lengths (28–31 days).

Decimal Age

Decimal Age = Total Days ÷ 365.25

Expresses age as a single decimal number by dividing total days lived by 365.25, the average number of days per year when accounting for leap years. Useful for statistical and scientific applications.