Use the shared matches tool at 23andMe, AncestryDNA, FTDNA, Living DNA or MyHeritage DNA to blow your family history mysteries wide open! Here’s how to use it to build your family tree and identify your DNA matches.

The very day that AncestryDNA’s shared matches tool first launched back up in 2015, I got up at 5:30 am with plenty of goals and ambitions. I didn’t end up doing much else that day.

Fast-forward to today, and the shared matches tools at this and other DNA testing websites can STILL help you solve more genetic genealogy mysteries than just about any other tool. Here’s what it can do for you.

DNA shared matches tool

The shared matches tools at 23andMe, AncestryDNA, FamilyTreeDNA, Living DNA and MyHeritage all help you identify DNA matches who are related to you AND to another match you already know. Basically, the tool helps you cluster together people who are related on similar branches of the family.

Let’s take a look at how this might work for you. (First, FYI, the shared matches tool goes by different names at different testing company websites. Learn what they are and how to locate them on each website.)

Let’s say you have a second cousin, Denise, whom you have already identified on your match list. You know your most recent common ancestors (MRCA) are Joseph and Louise Mitchell. You want to gather others who share DNA with both you and Denise. Those individuals then have a high likelihood of being related to Joseph and Louise in some way.

So we click on the shared matches tool for Denise. We find that Mike, Spencer, and Wendy all have DNA in common with you and Denise. After reviewing family trees, you are able to determine that Mike is related through Louise’s sister and Wendy is related through Joseph’s brother. (You see that Wendy’s actual relationship to you is not 4th cousin, as the site estimates, but she is actually your 3rd cousin once removed. Remember that the relationship given is not always the exact relationship of two people who have been tested. (Here’s how to better understand that relationship estimate.)

But what about Spencer? Spencer, unfortunately has not yet linked his family tree to his Ancestry account or answered any of your queries about his family tree. I am sure he has just been busy. Or he doesn’t know his family tree. Or his computer was captured by aliens or smashed by his two-year-old grandson just as he was about to click “send” and reveal how the two of you were connected. Whatever the case may be, up until this point you haven’t heard a peep from Spencer and therefore have absolutely no way to figure out how Spencer was related to you.

But now you know that he is somehow associated with the Joseph and Louise Mitchell family, because he came up as someone who shares DNA with both you and Denise.

Apply shared matches to a DNA match without a tree

We can take this one step further and ask Ancestry to show us who has DNA in common with you and Spencer. You can see from the graphic shown below that while Mike still remains, Wendy has dropped off the list. Now there are two possible explanations for this: The first is that Spencer is related through Louise’s parents, John and Sarah, and that is why he is not sharing DNA with Wendy.

The other, less likely, possibility is that Spencer is related through Joseph’s parents Louis and Mary, but doesn’t share enough DNA with Wendy to be detected on this test.

While this information is helpful, it still hasn’t completely solved the case. If you’re on Ancestry, look first to see whether Spencer has a tree that’s not linked to his DNA results.

If an unlinked tree doesn’t answer your questions, it’s time to follow up with specific questions to your matches. Sometimes your DNA matches don’t answer you. If you never hear from Spencer, the key to figuring out how he is related to you may be in the new match, Beth, who shares DNA with you and Spencer. If you can figure out how Beth is related to you, you will know Spencer is related in a similar way.

What to do next: Free guide to contacting your DNA matches

There are things you can do to increase the chances that Spencer (and your other DNA matches) will respond to you meaningfully. Over the years, through trial and error, I’ve learned what to say—and what NOT to say. I’ve summarized my best tips in a free downloadable guide. Please, help yourself to a copy!

Download free guide to contacting DNA matches