Calculating Date Of Birth from Life Events

  

Your tired.  You find an event (marriage, census, death etc..) in someone's life and know the exact date of that event and you also know the age of the person in years at the time of the event.  So now you can calculate something about their Date Of Birth (DOB) ... you take the year of the event and subtract their age in years ... but then it could be the year before or was it the year after depending on when their birthday fell in the year ?  Ahh ... if only there was a formula to help you.  Look no further help is at hand!

  

Case One - You know about the year only

  

Lets do the simple case first.  You know the year of an event and the person's age in years.  In what year was the person born?

  

Year_Of_Birth = Year_Of_Event - Age_In_Years - 1 OR
                         Year_Of_Event - Age_In_Years

  

So for example, suppose an event happened in 2016 and the person was 43 years old.  In what year were they born?

  

Year_Of_Birth = 2016 - 43 - 1 OR
                        2016 - 43

  

So the person was born in either 1972 or 1973.

  

Case Two - You know the exact date of an event

  

You know the exact date of an event and the person's age in years on the day the event happened.  What does this tell you about the person's DOB ?

  

If the event happened on a date of DD_MMM_YYYY then

  

DOB is FROM (DD_MMM + 1 day) and (YYYY - Age_In_Years - 1)
               TO (DD_MMM) and (YYYY - Age_In_Years) inclusive

  

So for example, suppose an event happened on 23 April 2016 and the person was 43 years old.  What can we imply about the person's DOB?

  

DOB is FROM (23 April + 1 day) and (2016 - 43 - 1)
               TO (23 April) and (2016 - 43) inclusive

  

So the person's DOB could be anywhere from 24 April 1972 to 23 April 1973 inclusive.

  

This level of precision can be very helpful if you have two life events for the same person where you know the date of the event and their age on each occasion.  By applying the formula to both events you can reduce the range of possible dates when the person was born to where the two ranges overlap.  Of course all this depends upon the accuracy of the information and so genealogists have to balance the precision of the formulae with the possible imprecision of the data.  Unfortunately there is no formula that can help with that !