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Common ancestor birth year finder

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  • Common ancestor birth year finder

    After getting some distant cousin matches on Family Finder, I found the task of calculating where to look for a common ancestor to be very repetitive.

    By deducting the birth year of distant ancestors to my birth year and dividing it by the number of generations separating us, I consistently came up with 33 years. That number seemed high compared to life expectancy, but considering males can become fathers through most of their life, and women historically gave birth to more children than now, it seems to work well as an average.

    First cousins share grandparents (2 generations back), second cousins share great-grandparents (3 generations back), etc. If I have a 4th cousin, our common ancestor is likely to be 5 generations away.

    When navigating trees back more than a few generations, you can easily lose your bearing. An approximate birth date of the generation you're looking for helps. The formula is simple: (my birth year) - (# of generations * generation span) = ancestor's birth year.

    I built a simple spreadsheet to display this info as a table for quick reference. I set my birth year and the generation span length as variables, and allowed for a range in generation span. I attached the file here for those who may find it useful.

  • #2
    Its a compressed zipped folder.
    How do I look at it?


    • #3
      The forum does not allow uploading Excel files, so I had to compress it. You should be able to download it and decompress it on your computer.

      For those weary of downloads, I added a screenshot that shows the formulas used so you can re-create it.

      If I have time, I may create a javascript version so it's web accessible.


      • #4
        I took the time to build a javascript version. It's not pretty but it works.

        In the bottom right panel, enter your birth year and the cousin level, then click "Find".