Date of Birth Calculator

Enter an age in years, months, and days plus the date that age applied to calculate the matching birth date with transparent calendar arithmetic.

Age on reference date · years

Months

Days

Reference date

—Calculated date of birth

This reverse calculation assumes the entered years, months, and days are an exact calendar age on the reference date. Records that state only an age in completed years describe a range of possible birth dates rather than one exact date.

Reverse an exact age

Enter the exact years, months, and days of age and the reference date on which that age applied. The tool subtracts those calendar components to return a corresponding birth date.

Records with age in years only

If a record says only “age 30,” the birth date is not uniquely determined. This page returns one exact date only when the months and days you enter are intended as exact age components.