Long Island Genealogy
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Birth Date Calculator

This calculator is a useful tool for genealogists. It is designed to calculate the birth date when the age at death and the date of death are the only facts known. As we all know this is often the only information recorded on older headstones.

Please make entries in each box on lines 1 and 2
Use a zero where you do not have a number to enter
Item Day Month Year
Date of Death 
Age at death in Days - Months - Years
Calculated Birth Date Will Appear Here - Day - Month - Year:

To perform your calculation enter data on both lines 1 and 2 
then press this button

Note regarding Birth Date Calculator:  While doing some testing on this with 30+ death certificates already containing a birth date, death date, and age, I have found it to be only 39% accurate.  It was 1-3 days off 38.5% of the time and more than 3 days the remaining 22.5%.  No one really knows exactly how stonecutter's figured the age of the person.  Did they use a formula, count off the days between birth and death, did they figure in Leap year?  Varying methods could have been used.  A friend has a different method of calculating a birth date and running the same test, found it to be only 22.5% accurate!  These methods work ok for approximate birth dates, but it should be understood that these date's are most likely not correct.  In running a several step process from when the stonecutter first figures the age from the birth date and carves the date on the stone and then someone tries to do just the opposite, there is lots of room to make errors along the way.
Tony Bengston