How Accurate Are Ancestry DNA Matches?

Solve your DNA Mystery Ebook

Discover your family’s story.

Enter your name to start your discovery.

You open up your Ancestry DNA results for the first time, and click on DNA Matches.  A long list of people that you’ve never heard of appear, and Ancestry DNA says that they are your cousins.  Some are first, second, or third cousins, and others are 4th-8th cousins.  Is this possible?  How accurate are Ancestry DNA matches?  You are not alone in wondering this – it is actually one of the most common questions.

In this article, you will learn about the accuracy of Ancestry DNA matches.  By the end, you’ll understand which of the matches on your list are absolutely accurate, and which matches you should be more skeptical about.

How Accurate Are Ancestry DNA Matches

The general answer to this question is that Ancestry DNA matches are very accurate.  Ancestry is one of the “Big 3” DNA testing companies, has a lot of experience in the industry, and an excellent reputation.  I personally have been using Ancestry DNA for several years now, and have had more than seventeen known immediate and extended family members test with the company.  I have found a high level of accuracy among the test results that I administer.

There are several things you should know about your DNA matches, however.  While the people who show up on your matches are definitely related to you in some way, there can be some leeway in interpreting how they are related to you.  Ancestry predicts your relationship distance based on the amount of shared DNA.  There is no other way for the software to know how you are related, since your family tree doesn’t show up in your DNA.  I’ll teach you when Ancestry’s prediction is always right, and when you need to look at the match with a more open-mind.

When the Ancestry DNA match prediction is always accurate

If you have a DNA match that shows up in one of these categories, the prediction is always* 100% accurate:

  • Parent/Child
  • Immediate Family
  • Close Family

The closer your relationship is to someone, the more DNA you share.  For this reason, it is easier for Ancestry to be extremely confident about two things:  the fact that you are related, and how you are related.  For every relationship type, there is a range of amount of DNA that is shared for that distance.  For close relationships, there is no overlap between the amount of DNA shared and the possible relationship.

What does it really mean?

  • If you have a match in the Parent/Child category, this means that the person is either your parent or child
  • If you have a match in the immediate family category, this person is likely a full sibling
  • If you have a match in the close family category, this person is like a half-sibling, full aunt, full uncle, niece, or nephew.  There is a small chance that this person could also be a first cousin, and you will have to know more details about the person to know for sure.

* The only situation that would cause the relationship prediction for these categories to be incorrect would be if there is an identical twin in the family – it happens, but it’s uncommon.

Ancestry's DNA Matches Are Pretty Accurate

Photo Credit: Richard Matthews CC by 2.0 License

When the Ancestry DNA relationship prediction is usually right, or almost right

As I mentioned previously, for every relationship type, there is a range of shared DNA that is usually found for that relationship distance.  Sometimes, that range can overlap with another relationship type.  For example:

  • First cousins typically have 575-1330 centimorgans (cMs) or 8%-18.5% matching DNA
  • First cousins once-removed, half first-cousins, and half-great aunts and half-great uncles usually have between 215-650 cMs (or 3%-9%) matching DNA

(Read this article to see how to find the number of shared centimorgans on Ancestry DNA)

You can see that there is a small overlap in the amount of DNA that is shared in those very different relationships.  Ancestry DNA has ways that they try to make sure they give you the best prediction.  For example, the closer in relationship you are, the more DNA segments you share, too.  But since your family tree isn’t written into your DNA, per se, they can’t tell you for sure.

Your matches that are in the following categories can be “almost right”:

  • 1st cousin
  • 2nd cousin
  • 3rd cousin

This means that when you have a DNA match from the above relationships, depending on where they fall in the range, could be placed in the “wrong” category, just because you share more or less DNA than average.  It doesn’t mean that Ancestry’s website made a mistake, it just means that you have to be careful and look at other evidence to figure out the exact relationship.

In order to figure out where they really are on your tree, or how they are related to you, you can try to find out more information about your match.   These are some ways you might be able to do just that:

  • What is their username?  Sometimes people use their surnames in their username, and this can give you clues
  • Do they have a family tree attached to their DNA or on their Ancestry profile?  Taking a peek at their tree can tell you a lot about how you might be related – including their approximate age.
  • If they don’t have a tree, you might consider sending them a message.  Ask them what the main surnames in their family are, so you can try to find a connection.

(Read this article to read more about contacting DNA matches)

Are DNA matches like rolling the dice?

Photo Credit: Peaches&Cream, CC BY 2.0 License

Sometimes, the Ancestry DNA relationship estimate is usually wrong

Since the way DNA is inherited appears to be completely random, this leads to the range of shared DNA.  You can share more or less than the average amount of DNA typically shared for any given relationship with your matches.  The more distant the relationship, the more overlap there is in the ranges for all “levels” of cousins.

For example, we will look at 3rd cousins.  3rd cousins can share 0 cMs of DNA, up to around 200 cMs.  That’s easy enough to understand, right?  The problem is that 3rd cousins once, twice, and three times removed, as well as 4th-8th cousins all share amounts of DNA that fall into that same range.

This means that the DNA matches in the 4th cousin category, which are typically estimated to be 4th-6th cousins from you, you will have to use more traditional means (see the previous section for ideas) to determine your relationship.  The same is true for those DNA matches that Ancestry says are “Distant Cousins” to you.   Ancestry DNA’s distant cousin category estimates that they are 5th-8th cousins.  As you can see from the 3rd cousin example, there is a possibility that you share a very low amount of DNA with a 3rd cousin, and because of that, they might show up in the distant cousin category.  This is unusual, but possible.

This is the major reason why it’s still an excellent idea to not ignore your 4th-8th cousin matches, since many of them will be more closely related to you than the Ancestry DNA prediction, and can provide valuable information for finding family and researching your family tree.  Yes, many of them will be distant cousins, but some of them won’t be.  It’s worth a look.

(It is important to note that 10% of 3rd cousins and 50% of 4th cousins will share no DNA at all.  The more distant the cousin relationship, the less likely it is that there will be shared genetic material between two cousins, even though you are still related in a genealogical sense.)


I hope that this article has helped you understand the way that Ancestry DNA groups matches into categories, and whether or not those relationship predictions are accurate.  If you have a DNA match that you are puzzling over, I’d love to hear about it in the comments.

Thanks for stopping by!




How Accurate Are Ancestry DNA Matches?
Article Name
How Accurate Are Ancestry DNA Matches?
Are your Ancestry DNA matches accurate? Find out when they are accurate, and when you might need to look more carefully at the match.
Publisher Name
Who Are You Made Of
Publisher Logo