Leeds Method: Which Matches Should You Use?

I often get questions about which matches should be used when doing the Leeds Method. For the most part, it depends on what you already know about your family and matches.

Unknown Biological Parent or Grandparent

If you are trying to identify an unknown biological parent or grandparent, you probably don’t know your 2nd and 3rd cousins. In that case, I recommend using matches who share between 90 and 400 cM of DNA with you. This is because we are hoping to find 2nd and 3rd cousins and avoid any first cousins who share two grandparents with you. And, for most people this range works.

(Read this post to understand why we want 2nd cousins but not 1st cousins.)

Known Biological Parents and Grandparents

However, if you know your biological parents and grandparents and are able to identify some of your matches, you should use those matches who share only ONE grandparent with you and avoid those who share TWO grandparents with you.

Above I’ve shared a diagram of me and my first cousin once removed (1C1R), “Dave.” We share 350 cM of DNA. Let’s look at two scenarios:

1. 1. If I were creating a Leeds Method chart and he was a “key person”—that person who started a color cluster and I used his Shared Matches to create the color cluster—then the chart would be fine. He shares only one of my grandparents with me: Hazel.
   2. If he was creating a Leeds Method chart and I was a “key person,” then that color cluster would include matches from two of his grandparents: Emil and Myrtle. Instead, he should exclude me on his initial chart.

Why avoid 1st cousins?

When using the Leeds Method, we are hoping to discover four clusters based on our four grandparent lines. First cousins, however, match us on either our dad’s or our mom’s side. If we created clusters based on them, we could potentially only get 2 clusters instead of 4.

Can I add in 4th cousins?

I suggest creating the initial chart first. But then, yes, you can add in 4th cousins. In fact, it’s encouraged!