How to use the birth date from age at death calculator
- Enter the date of death.
- Enter the age in years at death. Add months and days if the record gives them.
- Read the earliest and latest possible birth dates, or the single calculated date when months and days are given.
- Check the result against a birth record or another source before relying on it.
Formula
Years only: latest birth = same calendar day n years before death
Years only: earliest birth = the day after the same calendar day n + 1 years before death
Years and months: subtract the total months from the date of death
Years, months and days: subtract the months, then the days
A person who is n years old on a date has had n birthdays but not yet the next one. February 29 is moved to February 28 in years without one.
A death on June 15, 2020 at age 72
A person who died on June 15, 2020 aged 72 was born between June 16, 1947 and June 15, 1948, a window of 366 days. The latest date means they were 26,298 days old. If the record gives 72 years and 3 months, the birth date is between February 16 and March 15, 1948. If it gives 72 years, 3 months and 5 days, the date is Wednesday, March 10, 1948.
Someone who died on February 29, 2020 aged 1 was born between March 1, 2018 and February 28, 2019.
Reading old records
Gravestones, newspapers and death certificates often give an age instead of a birth date. The age may be exact to the day, rounded down to years, or approximate if the family did not know. A range from this page is a starting point for searching baptism, census or birth records near those dates.
To work with the dates once you have them see the age calculator, the date calculator and the days between dates calculator. Relationships can be mapped with the family tree maker.
Months and days in the age
When months and days are given, the date is found by counting backward. Months have different lengths, so the same age can fit a birth date one day off from the true one. That is why the page notes that an exact date can still be a day away. Treat the result as strong evidence, not proof.
Assumptions and limits
- The age is the completed years (and months and days) at the end of the date of death.
- The calendar is the modern Gregorian one, with years from 1000 on; older calendar changes are not modeled.
- Months run from 0 to 11 and days from 0 to 30, and days need months.
- A recorded age can be wrong, so the range is only as good as the record.
Frequently asked questions
How do I find a birth date from an age at death?
Go back that many years from the date of death. The person was born on or before that date and after the day one more year back, which gives a range of about a year.
Why is there a range of dates?
An age in whole years fits every birthday over a span of 365 or 366 days. Only an age with months and days narrows it to a single date.
What if the person was born on February 29?
The page moves February 29 to February 28 in years without a leap day, and counts the birthday from March 1 in the age rule it uses.
How accurate is the result?
The arithmetic is exact. The result is only as accurate as the age in the record, so confirm it with a birth record.