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Birthdate Calculator - 

Estimates Date of Birth Using Death Date and Age

by Cliff Lamere    18 May 2003


This calculator by Ben Buckner uses the Gregorian calendar in which the New Year begins on January 1, instead of the J ulian calendar which had New Year on March 25.  The latter calendar was used in England and English colonies until 1752.  New Netherland (later New York), a Dutch colony, used the Gregorian calendar until 1664 when the English took control, then the Julian calendar until 1752, then returned to the Gregorian calendar.  The two calendars also differed by 10 days before 1700 and 11 days after 1700.  This had quite an impact on dates.  In an extreme case, a person born Jan 31, 1660 in New England would have been born the same day as a person who came into the world in New Netherland on Feb 10, 1661 (appearing to be almost 12 months later!!).  


For more information, see the notes below the calculator, and also my webpage:  

Julian and Gregorian Calendars - Effect on Church and Civil Records


Directions:  In day-month-year format, enter the date of death and age at death before computing the date of birth.  If any number is missing, the calculator will not work.  You can substitute a 0 for a missing number, but the poorer the input, the more inaccurate the answer will be.


Birthdate Calculator
















There are many Buckner birthdate calculators online.  They seem to be of two types, only one of which accurately calculates all February dates.  The calculator on this webpage will display February 28 rather than February 30 or 31.  In leap years, it will accurately display February 29 as the date.


The two types of calculators display the calculated month differently, thereby making them easy to distinguish from each other.  If the month is shown as a 3-letter abbreviation (for example, Oct), then not all February calculations will be correct.  If the month is shown as a number, February dates will be calculated correctly.  However, the numbered month confuses some people.  An answer of     1   3   1920    can be interpreted as January 3 or March 1.  It is intended to be March 1.  I have added the words Day, Month, and Year to the ANSWER windows above so that you will not likely misinterpret the answer.  When I was trying to provide a link to an accurate calculator from my website, I could find no calculator with that feature.  The result is that I made my own webpage.


Some online Buckner calculators allowed a choice of using 30-day months or calendar months (the accurate number of days per month).  However, seldom did the calendar month option work in those calculators.  




Caution:  Undertakers used various methods to determine the person's age at death which appears on a gravestone.  Because we cannot know the method used to make the original calculation, today it is impossible to be certain about the true birth date of a person no matter how accurate the calculator may be.  When recording the date you determined by using a calculator, the date should be preceded with something that makes it clear that the date is not certain.  Examples would be:     about     abt.     c.     circa     .  Or, you may want to describe the date as "estimated".  Personally, I use c. because it is the shortest.




The calculator on this webpage uses the Gregorian calendar (developed by Pope Gregory XIII) which begins each year on January 1.  The previous Julian calendar (developed by Julius Caesar) had the year begin on March 25.  Roman Catholic countries (and regions of countries) in Europe quickly adopted the Gregorian calendar which was proposed in 1582.  Protestant countries did not.  


The Dutch in New Netherland (later called New York) were using the Gregorian calendar when the English took control of the colony in 1664.  This meant the return to the Julian calendar (until 1752 when England and its colonies made the switch).  This also meant that "double dates" were often recorded.  You may have seen a date like 10 Feb 1720/21.  To correspond with today's dating system, you would record the double date as 10 Feb 1721, ignoring the difference in the number of days unless it is important for some reason.  Double dates occur only for the dates from 1 Jan to 24 Mar.  (see comments in the introduction at the top of this webpage for more details.)


Albany & Eastern New York Genealogy

Visitors since 18 Mar 2003