Birth and Death Date Calculators

Online Birth and Death Date Calculators

Name	Website	Description
Birth Date Calculator	longislandgenealogy.com	Used to help you calculate birth date when the tombstone only gives the date of death and the exact age
Date Calculator	Calculator.net	General date calculation site but calculates birth/death dates the way genealogical records do.
Age Calculator	Rootsweb	Has 4 various calculators to determine birth date and age including the **8870 method
Ancestor Search Age Calculator	searchforancestors.com	Used when you want to determine the date of death from a birth date and exact age
Tombstone Birthday Calculator	searchforancestors.com	This calculator allows Julian calendar or Gregorian dates to help you calculate birth date when the tombstone only gives the date of death and the exact age. This calendar also allows for a 30 day month or **(8870) method

Calculating Dates Using Online Calculators

There are two ways to calculate a date from an age at death:

• 30 day month method; example: 28 Apr 1864
• exact month method; example: 30 Apr 1864

This can be explained with this example: Death date: 13 Mar 1870 Age at death: 5 years 10 months, 13 days, Two answers can be given: Exact month method: 30 Apr 1864 30 day month method: 28 Apr 1864

Which Way is Better?

That just depends on how you wish to calculate the date. The 30 day month method assumes that all months have 30 days, whereas the exact month method uses the exact amount of dyas for each month.

Although, the exact month method would be more accurate when calculating a date. Some believe that the dates and ages calculated and found on tombstones uses the 30 day month method.

Records that may give an exact age at death and a death date can be found on:

Death records Grave markers (typically older markers)

Church records Obituaries

Tips for Using Date Calculators

• Be aware that some of these Websites have other types of calculators with different functions, explanations and tips, with various kinds of information. So check out the rest of the page. (The following examples are what you might find for tips)
• Some calculators may require you to put a 0 in a box instead of leaving a box blank, also using a 0 in front of a single digit month may or may not be required.
• Due to possible errors or different methodology used in Calculated dates from original calculations. (found on the tombstone, obituary or death certificates) , please make a note in your records that the date was calculated..
• The calculator could also be used to calculate birth year from census data or birth date from wedding date and age.
• When calculating Dates using the Julian or Gregorian Calendar you can't use the two together.
• There is what is called a 30-day-month/or **8870 method which assumes that all months have 30 days, many of the headstones and obituary ages at death appear to have been computed using this method. It's an approximation which agrees with the exact calendar month method about 2/3 of the time.)
• 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 the calendar was changed from Julian to Gregorian in which ever country for which you are performing the calculation. See the change from Julian to Gregorian calendar Dates by country.

How to calculate by hand - Estimated date

There is what is called a 30-day-month/or **8870 method which assumes that all months have 30 days, many of the headstones and obituary ages at death appear to have been computed using this method. It's an approximation which agrees with the exact calendar month method about 2/3 of the time.

When the online calculator is not available, use the **8870 formula or the 30 day month length

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

18890506 Year, day, month of death (yyyymmdd) 1889--05--06

-710709 Subtract age at death (yymmdd) 71yr-07mo-09dd 

_________ 18179797

   -Subtract constant 8870

________ 18170927 Born 27 Sept. 1817 (yyyymmdd) 1817yr-09mo-27dd

This person was born on September 27, 1817