This birth from death date calculator works out when a person was born from just two facts: the date they died and their age at death. It is the classic family history problem posed by a headstone or a death record that reads died on a certain date, aged so many years, with no date of birth given. Enter the date of death and the age at death in completed years, and the calculator returns the possible year of birth along with the earliest and latest dates the birth could have fallen on. There are always two candidate years rather than one, because an age counted in whole years does not tell you whether the person had already had their birthday when they died. If they had, the birth year is the death year minus the age; if their birthday was still to come, it is one year earlier again. The calculator brackets the answer between the latest possible birth date, which is the age in years before the death date and assumes they died on their birthday, and the earliest possible birth date, the day after they would have turned a year older. That roughly one year window is the tightest you can get without a known birthday. The defaults describe someone who died in March 2020 aged 72. Change them to your own record, and see the worked example below.
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years
1947 or 1948
possible year of birth
Latest possible birth date15 March 1948
Earliest possible birth date16 March 1947
Age at death72 years
The birth year cannot be pinned to one figure without a known birthday, so both candidates are shown. Dates are the standard Gregorian calendar; historical records before 1752 may use older calendars.
How it works
Age at death is the number of completed years between birth and death, which leaves the birthday itself hidden. Subtracting the age from the death year gives the later candidate birth year, the one that holds if the birthday had already passed that year. The year before it is the other candidate, for the case where the birthday was still ahead. To bracket the exact date, the latest possible birth date is the death date shifted back by the age in years, which is the born-on-your-birthday case, and the earliest possible birth date is the day after the person would have turned one year older, because any earlier and they would have reached the next age before dying. The true birth date sits somewhere in that window of a little under a year.
Worked example
Suppose a record shows a death on 15 March 2020 at age 72. Subtracting 72 from 2020 gives 1948, the later candidate birth year, with 1947 the earlier one. The latest possible birth date is 72 years before the death date, which is 15 March 1948, the case where the person died on their 72nd birthday. The earliest possible birth date is the day after they would have turned 73, which is 16 March 1947. So this person was born between 16 March 1947 and 15 March 1948, in either 1947 or 1948 depending on where their birthday fell in the year.
