Ancestor Search Birthday Calculator

Many older tombstones list age and date of death. This tool calculates birth date from the age of death and the date of death on the tombstone, death certificate or obituary. Results are given in a year-month-day format


Enter the person's date of death and age at death:

Month Year
Do not leave any blank spaces
Use a zero instead of a space
  Days Months Years
Do not leave any blank spaces
Use a zero instead of a space

Click to calculate birthdate:        

Birthdate Calculator Tips for Usage

  • Calculated dates should only be considered approximate due to possible errors or possible different methodology used in the original calculation (found on the tombstone, obituary or death certificate). Be sure to note in your records that your date was calculated.

  • This calculator can use either the exact month method or the 30 day month method to compute a birthdate. While you may think the exact calendar month method may be more reliable, be aware that many of the headstone and obituary ages at death appear to have been computed using the 30-day-month method. (The 30-day-month method assumes that all months have 30 days. It's an approximation which agrees with the exact calendar month method about 2/3 of the time.)

  • A tombstone or death certificate is not considered a primary source for a birthday, but it can give you an approximate date of birth to help in further research.

  • The calculator could also be used to calculate birth year from census data or birthdate from wedding date and age.

  • The calculator allows Julian calendar dates, but you cannot mix Julian and Gregorian dates or ages in the same calculation.

  • Because of the change from the Julian to the Gregorian Calendar, the calculator may not work for anyone born between Sept. 2, 1752 and Sept. 14, 1752 (or when days were lost at the calendar changeover.

  • Be aware of when the calendar was changed from Julian to Gregorian in the country for which you are performing the calculation. See the change from Julian to Gregorian calendar by country.

  • To do this calculation by hand when the online calculator is not available, use the 8870 formula.(the calculator calls this the 30 day month length)

  • If a person died May 6, 1889 at age 71 years, 7 months and 9 days:

  • 18890506
    Year, day, month of death (yyyymmdd)

  •  -710709 Subtract age at death (yymmdd)
  • _________
  •     -8870 Subtract constant 8870
  • ________
    18170927 Born 27 Sept. 1817 (yyyymmdd)

  • This person was born on September 27, 1817

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