Determining Cousins – My Formula/Process

Determining Cousins

I was recently asked by a family member how to figure out cousins, 1st, 2nd, 3rd, and so forth and what “removed” means.  What makes someone a first cousin once removed, and so forth.
First, there are many charts on the Internet that show how to figure out the relationships. I have pinned several of them to my “Genealogy – Cool stuff I find” board on Pinterest.
When I use a chart, I use Blaine T. Bettenger’s chart most often.  Not only does it show the cousin relationships, it also shows the average number of centimorgans of DNA you would expect from a particular relationship and a range matching to show relationships.  I like this one because it shows the DNA amounts for various relations. My link to it is via the DNA Testing Advisor.com page on DNA Relationship Data. (By the way, I’m very excited to be seeing Blaine Bettenger, Ph.D., J.D. speak at the Maine Genealogical Society’s 2016 Spring Workshop this April 23.)

My Formula/Process

I don’t think I’ve seen this method anyplace, but it is the method I use and it works really well for me.

First, determine the common ancestor two people
share. Second, count the number of generations to the common
ancestor for person number 1. (For example, it is 4 generations to my 2nd
great grandparent.) Third, count the number of generations to the same common ancestor for person number
2. (for example, 5 generations to the same
person.) Take the smaller number and subtract one. That gives
the cousin number. (for example, above person #1 is 4 generations to a
common ancestor, subtract 1.  Whoever I
share that common ancestor with is a 3rd cousin.
 Finally, take the larger generation number and
subtract the smaller number. That defines the “removed” number.  (In the
above example, the larger number was 5 generations, minus 4 generations, equals
1, or once removed.

So, if Marion (Sanford) Brown is my 2nd great grandmother and Marion (Sanford) Brown is your 3rd great grandmother, we are third cousins once removed. 
Try it a couple times and you will find it works really easy. It is how I do it and it works well for me.
So, cousins are defined by who you share a common ancestor with, removed is defined by the generational difference between you and a cousin. 
– Don Taylor
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