Shared cM | How Am I Related to My DNA Matches?

You’ve found a DNA Match you don’t recognize. That’s not uncommon! Family trees attached and tools such as the Shared cM Project can help you discover your relationship. Follow these three steps to finding that relationship–the Shared cM Project comes up in #2.

Strategies for Finding Your Relationship to Your DNA Matches: The Shared cM Project

1. Ask them who they are.

Before you even start using the Shared Centimorgan Project, you can reach out to your DNA matches and ask them what they know about their birth roots. Between the two of you, you may be able to figure it out. However, connecting with your matches can be something as tricky or sensitive as a first date. Just like any first date, there are things you can do to increase your chances of a second date (a response from your DNA match). These strategies can be found in my FREE Tips for Contacting Your DNA Matches.

2. See how much DNA you share with your match.

The biggest clue you get with every single DNA match is your amount of shared DNA. This is reported in cM, and sometimes as a percentage (23andMe only includes the percentage.) Some testing companies also list your possible genealogical relationships. This information will be similar to what you’ll be able to see for yourself at the Shared cM Project, our next destination.  

3. Take shared DNA data to the Shared cM Project

Blaine Bettinger spearheaded this collaborative effort we now call the Shared cM Project. He collected the shared cM data for known relationships from genetic genealogists just like you. The resulting free chart gives you a good estimate of how much DNA should be shared for different relationships. Here’s what the chart looks like (it may be updated over time):

How to Use the Shared cM Project

This short video demonstrates the Shared cM Project for you—and tells you when you need it.

For each DNA match, you can see on the chart what kinds of genealogical relationship best fit your total shared DNA. For example, if I share 69 cM with my match, we might be third cousins. But we might also be second cousins once or twice removed.

(Note: If you tested at 23andMe and only have a % of shared DNA, use the interactive chart below to convert that to cM or multiply the percentage by 74.5).

Jonny Perl and Leah Larkin have taken the Shared cM Project even further. They created an interactive Shared cM relationship chart on the DNA Painter website. Input the shared cM value to see the possible relationships and statistical probabilities for the likelihood of each of these relationships. This tool has TWO versions. One reflecting some original probabilities, and the Beta version (accessed by clicking the small, green “Beta with updated probabilities” on the left) with the most up-to-date estimates.

Notice in the above case that it is about 38% likely that you have one of those four listed relationships. A half 2C would share one of your 8 great grandparents. A 2C1R is a second cousin once removed, and indicates that this person is on a different generation than you are; they are either older or younger than you.

It is important to realize that these numbers are just estimates and honestly, as long as the probability of your relationship isn’t zero, you are probably OK. These numbers are just for you to use as a guide to help you know when you should start looking for your common ancestor with your match.

Next steps: Discovering the right relationships for your DNA matches

Now, how do you determine which is the correct relationship? It’s time for a two-prong approach.

Contact your DNA matches. I know. We said this already in the first step above. But sometimes it takes a couple of tries to get a real conversation going. It can be intimidating. That’s why we offer a free downloadable guide to contacting your DNA matches. If you didn’t grab it above, get it now:

Do genealogy research! It’s time to use traditional records and research skills to better understand the genetic clues in your family history mysteries. Read our free articles on the kinds of records and techniques that help you build a better family tree for your DNA matches.

Learn to Do the DNA—faster and with confidence

When it comes to identifying your DNA matches, you want to get it right. And you don’t want to go in circles or get lost in your analysis of who’s related to whom and how. (Believe me, it happens!)

My book is the ultimate step-by-step, do-it-yourself guide to figuring out how you’re related to your DNA matches. It even has special sections for what to do about specific situations that come up, like cousin intermarriages, endogamy, half-relationships, unexpected connections, unresponsive DNA matches and more.