How Accurate is AncestryDNA?

As consumers we are always seeking the best products or at least the ones that best suit our needs and circumstances. It’s only logical then that if we are going to pay cash to get something like a genealogical DNA test we want to know it’s good.

In this post we are going to look specifically at AncestryDNA to try and determine how accurate their tests are. We will look at all the aspects of the results they offer and assess how valid and worthwhile an AncestryDNA test is.

How Accurately Does AncestryDNA Test Our DNA?

We only have AncestryDNA’s word for this but according to the site itself they have an accuracy rate of 99% for each genetic marker they test. As they do not share their exact processing techniques we can only really take their word for this statistic.

It should be noted however that our DNA is what it is so as long as they receive a viable sample and they have a solid testing process then the accuracy should be relatively good. This is of course only referring to their ability to read our DNA, not necessarily the interpretation of the results.

There is understandably one set of circumstances whereby accuracy could be completely compromised and that would be if the company ever mixed up samples. Well none of the big testing companies have ever released data regarding any mixed up samples but It is safe to say based on human fallibility it must have happened at least once or twice.

Generally speaking though in the first phase of the testing Ancestry does have a good record and they seem to know what they are doing when it comes to reading our DNA. Though there are questions about accuracy when it comes to the DNA tools they offer.

Ethnicity Estimate

One of the biggest reasons most people sign up for an AncestryDNA test is the ethnicity estimate. In fact their marketing leans very heavily into this aspect of the test. You have probably seen the heartwarming commercials about people discovering their heritage. Just how accurate are these estimates of our ethnicity?

Well AncestryDNA, as do all the other testing companies, cover themselves by making it clear that these ethnicity estimates are just that, estimates. What they essentially do is read segments of our DNA that match to common segments that are usually found in individuals from specific regions.

The algorithms that do this work are very impressive and I can’t even begin to understand how they do it. Generally speaking the larger estimates are usually quite accurate but when we get into the more trace regions the accuracy can fail a little.

This is because sometimes our DNA may recombine in a certain way to create a segment that looks like something else. We may have a segment that appears African in nature but it was just a random recombination. It may not in fact indicate a distant African ancestor.

This was likely the case when I got my first test results several years ago. I was assessed as having an estimated 1% Native American DNA result. I am very British. My ancestors going back two centuries were all very British so it didn’t make sense.

Within a few updates the Native American DNA disappeared from the estimate but of course my DNA never changed so why would that be? The simple answer being that initially it looked like a segment of my DNA may be Native American. As testing improved it would become apparent that this was incorrect.

In the most recent update back in September of 2022 my results were pretty accurate when I compared them to my known ancestry on paper. There is nothing unexpected and nothing below a 2% estimate so for me it seems very accurate.

This may not be the case with everyone and of course because we do not always inherit DNA from all of our ancestors we may not see our entire ethnic background. Someone with a known great-great-great Native American ancestor might not actually inherit DNA from them.

Even though the Native American ancestor is part of our bloodline, if we do not inherit their DNA then it can not show up in an ethnicity report. In this instance AncestryDNA is only inaccurate because the DNA is not there for them to find.

DNA Matches

A big favorite of mine is the DNA matches with those hundreds of potential cousins we discover. Just how accurate is this match list though? Well as with the ethnicity estimate the result's accuracy depends on how much DNA we share with the other sample.

When we share a lot of DNA with these matches then the likelihood is that we share a recent common ancestor. AncestryDNA are good at reading our DNA and they are also good at finding those we match with thanks to their very extensive DNA database.

As with ethnicity estimates however when the shared DNA percentage gets lower we do enter a range where we might find the match is simply accidental. Sometimes the DNA we share with someone else is the result of recombination and not inheritance. This would mean that we do not actually share a recent common ancestor.

So in terms of AncestryDNA’s accuracy in cousin matches they get it correct when we share a lot of DNA with a match and they are good at offering potential ways we may be related. The more distant the match and the less DNA we share the more likely it is that it is purely coincidental.

Thrulines

This third tool that AncestryDNA offers is to my mind the least accurate of the three. It uses DNA matches and the content of your tree when compared to the DNA matches tree to estimate your relationship.

I have found a few of these estimates to be correct but only after I fully check each connection they made for the estimate. There have however been some that were completely wrong.

The reason this is a very flawed tool is because it relies on the accuracy of our family trees. I am confident in the accuracy of my own tree but that is only after a decade of research and learning from some pretty fundamental mistakes.

There are trees out there that are just terrible with people being assessed as the parents of others when they were just 4 at the supposed child’s birth. I have seen so many ridiculous errors which are glaring because to my shame I made some of them too in my early days.

We can generally trust the DNA match as long as it is to a high level but we can not always trust each other's trees and as such Thrulines can be very inaccurate.

Conclusion

When it comes to reading our DNA AncestryDNA are pretty accurate and seem to know what they are doing. It is when it comes to interpreting our DNA that we start to see some inaccuracies. When our matches are of a low percentage then mistakes are very possible.

That said ethnicity estimates and DNA matches are both fairly accurate at the higher levels so they are certainly worth taking the test for. Thrulines on the other hand although fun in theory can be wildly inaccurate. If you are to use it you must remember to test the connections they suggest before they assume them to be correct.

Neil Edwards

Genealogist and family-tree research specialist

Neil was born in Shropshire, England surrounded by centuries of living history. His interest in the past has been a lifelong passion leading to undergraduate degrees in both Economic History & Geography and History & Politics.

This interest in history quickly translated to family history when he moved to the U.S. in 2010. It was here that he began working on his own family tree as well as that of his American wife. That research allowed him to gain a wealth of experience working with both U.S. and European genealogical documents and studying their best uses in researching family history.

Following 9 years of honing his genealogical research skills, Neil was proud to have earned a certificate in Genealogical Research from Boston University in late 2019. Neil also took part in the research process for a Duke University study into the families of 19th Century UK Members of Parliament.

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