How the birth year is worked out
Subtract the age from the year of the “age on” date. If the birthday hasn't come yet that year, the person was born one year earlier. When you don't know, both years are possible, so the calculator shows both.
Example: someone is 30 on November 6, 2026. If their birthday has already passed in 2026, they were born in 1996; if it's still to come, in 1995.
Ages on documents and records
Census forms, ship lists and certificates often record an age instead of a date of birth. Set “Age on” to the date of the record to get the birth year it implies. Ages on old records were sometimes rounded, so treat the result as a starting point and look for a birth or baptism record to confirm it. For ages at death, the age at death calculator can work back to a full date.