How Many Centimorgans is a Good Match?

Do you want to know how many centimorgans is a good match? In this post, learn how to determine whether cMs shared between two DNA matches is significant.

The DNA match list can be both exciting and confusing. Almost everyone on your list is likely to be related to you in some way, but figuring out how to evaluate your matches is difficult.

Many people have many hundreds, if not thousands, of people on their DNA match lists, which means that we need a strategy to evaluate our DNA matches.

With so many potential relatives on your DNA match list, where should you start? Is there a best way to decide which DNA matches you should focus on?

One of the first things that you might wonder about is how much DNA shared to between two people is actually significant? Understanding how the number of centimorgans (cMs) that our relative shares with us can be key to learning how we are related.

What is a high cM DNA match?

What is a high cM, or significant DNA match? The answer is: “it depends,” as who is significant to one person might be different for someone else.

What we might define as a significant DNA match will vary depending on what we are trying to learn about our ancestry and how much we already know. Then, when we research our DNA match, we will weigh the amount of shared DNA in relation to our current knowledge about our family tree.

This means that a “significant DNA match” will be different for everyone.

Even so, we could all agree that having a previously unknown DNA match pop up on our list that could be related as a parent, grandparent, full or half-sibling, aunt or uncle, niece, or nephew, or even first cousin, would be considered significant to most of us.

With this in mind, we can define a high cM match as someone who shares at least about 900 centimorgans, or almost 12.5% of our DNA with us. At lower amounts of shared DNA, the relationship possibilities expand greatly, and include more distantly related relatives.

Even though someone who shares less DNA with us might not be as close a relative as those that I mentioned above, we can still find the relationship to be meaningful. In addition, we can also learn a lot from people who are not as closely related.

This brings us to the next question. And, as you might suspect, the answer is equally subjective.

What is considered to be a good DNA match?

A “good” DNA match, in relation to the number of centimorgans shared, would be someone who shares enough DNA with us to make the identification of a common ancestor likely.

For the sake of discussion, we can try to put a more precise definition on what makes a DNA match important for family tree research. We could assume that most people in the United States could eventually, with good research, be able to learn enough about their family tree to identify their ancestors as adults on the 1870 US Federal Census records.

Depending on how old a person is today, ancestors born between 1850-1870 might be as closely related as a great-grandparent, or as distantly as a great-great-great-great grandparent.

Relatives who are descended from these ancestors are related to us as closely as second cousins, and as distantly as fifth cousins.

Therefore, we could define a DNA match with whom we are likely to be able to identify our common ancestor as someone (a.k.a. a “good DNA match”) as someone who shares more than about 20-30 cMs with us. Ideally, the shared DNA would be one 20-30 cM shared DNA segment, instead of more smaller segments equaling 20-30 cMs.

I decided upon the 20-30 cM threshold for a match being significant in most cases because the majority of people who self-reported shared DNA with their 5th cousins to Blaine Bettinger’s Shared cMs Project detailed amounts between 20-39 cMs.

We know that identical DNA segments that are larger than 20 centimorgans are fairly unlikely to be false segments. This means that we can research our family trees and those of our DNA matches with the knowledge that it might be possible to find a genealogical connection with them.

All DNA matches are good matches

You might have noticed that the threshold that I identified above for what equals a significant, or good, DNA match, includes a great number of your matches. Coincidentally, or perhaps not, this is because all of our DNA matches are good matches.

Each person who is on our DNA match list who shares over about 20 cMs with us is likely to be related to us in some way. In this way, researching each DNA match has the potential to teach us something very valuable about our ancestry and family tree.

With so many good DNA matches and so little time, is there a best way to approach evaluating your DNA match list?

How to research your DNA match list

For best results, you should approach your DNA match list in a methodical fashion. Starting at the very first match, which is likely the person most closely related to you on your list, determine who you share as a common ancestor.

For tips to help you figure out how your DNA match is related, read this post:

• How is your DNA match related? Here’s a checklist.

As you work down your list, it is best to take good notes about how you are connected to each DNA match. In addition, starting a small family tree where you can add in your shared ancestor, and the line leading down to your DNA match, is best practice.

This will make it easier to spot how you are connected to other matches.

As you move in to your second and third cousin DNA matches, you might find people whose names are unfamiliar to you. You might considering using the Leeds Method to group these DNA matches into groups sharing common ancestors.

Depending on where your more recent ancestors were born, you might have a great number of DNA matches that are related more distantly than 2nd-3rd cousin on your list. In fact, some people have several hundred DNA matches – or more – estimated to be 4th-6th cousins (like on Ancestry).

It’s important to note that some of those relatives who are estimated to be more distantly related to you might be “half” cousins who only share one common ancestor. The result of this is less shared DNA with closer relatives, so don’t skip the chance to research those more distant cousins.

The number of DNA matches that you decide to research is completely up to you. It all depends on how much time you have and what you would like to learn about your family tree.

Conclusion

I hope that this post has helped you understand more about what makes a DNA match significant, and how to evaluate the amount of DNA that you share with your match in relation to what you know about your family tree.

If you have any questions about something that you read in this post, or if you would like to share a specific question about a number of centimorgans shared with a match, please feel free to join us in the discussion below.

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