If you tested your DNA with Ancestry, and are trying to make sense of you DNA match list, you are not alone! Those of us who use Ancestry DNA use fourth cousin matches as a guidepost of how many “good” DNA matches we have, since these cousins (and their family trees) can help us learn about our family history.
In this post, I will help you understand the following:
- What a 4th cousin is, which is different than a 4th cousin DNA match (you’ll understand why)
- What a 4th cousin DNA match is
- How to know how you are related to your fourth cousin matches
- Why fourth cousin matches are useful
Ready to get started understanding your very valuable fourth cousin matches?
What is a 4th cousin?
An actual fourth cousin is a person with whom you share great-great-great grandparents. You could share a set of great-great-great grandparents, or just one great-great-great grandparent. If you only shared one great-great-great grandparent, then you would be, technically, a half-fourth cousin.
To put your relationship with a 4th cousin in perspective, you have 32 great-great-great grandparents, so you will share 2 out of 32 of these ancestors in common with your fourth cousin. In the case of a half-fourth cousin, you will share 1 out of 32 of these grandparents.
Why is a fourth cousin sometimes different than a fourth cousin DNA match? Keep reading to find out!
What is a 4th cousin DNA match?
You might have noticed that Ancestry DNA has grouped your DNA matches into various categories, ranging from Immediate Family, to 4th Cousin, to Distant Cousin.
As it turns out, Ancestry DNA is only able to estimate your relationship to your DNA match, based on the amount of shared DNA and the number of shared DNA segments.
For this reason, people who are in the 4th cousin category on Ancestry might not actually be fourth cousins. They could be much closer, or much more distant than an actual fourth cousin.
Some of your 4th cousin DNA matches are actually 4th cousins
As you already know, a 4th cousin shares great-great-great grandparents with you. This means that you can have an awful lot of fourth cousins out there somewhere, and it’s unlikely that you know any of them – most people don’t grow up knowing any fourth cousins personally.
The average person could have between about 900-1500 cousins. Obviously, the exact number of fourth cousins that you actually have depends on how many children your great-grandparents had, how many children their children had, and so-on and so-on.
Even so, the average family, having 2-3 children per generation, will grow exponentially, creating a surprising number of descendants fairly quickly.
This whole conversation about 4th cousins has got me thinking about my own family. My grandmother on my dad’s side and her siblings have made a concerted effort to keep our family “together”, even though we live spread out all over the whole country.
A number of our extended family members get together occasionally for a great-uncle’s birthday, or a second cousin’s wedding. I’m the oldest great-grandchild on this side of the family, so most of my second cousins don’t have children yet, but I can imagine a day when our children know each other (they would be third cousins) – and maybe even a day when a few of our grandchildren know each other – fourth cousins!
In other words, it is definitely possible for distant cousins to know each other growing up, but it is unusual and it takes a lot of effort these days when people live so far away from each other.
It seems shocking to imagine that me, and all of my second cousins might eventually have over 200 descendants – contributing our share of the total of 900-1500 fourth cousins to our grandchildren. Yikes! That would be a lot of birthday presents – maybe it is better that we lose track of each other 😉
How much DNA should you share with a 4th cousin?
Since your fourth cousins are not very closely related, there are some important things you need to know about your DNA relationship:
- You will only share DNA with about half of your 4th cousins
- Of those fourth cousins with whom you do share DNA, you will share an average of about 13 cMs (centimorgans)
- The range of shared DNA between fourth cousins can range from 0-125 cMs (the exact range is up for debate, since some experts say that upper limit is around 125 cMs, and others say that the higher end of the range is much lower, at about 40 cMs. A higher number of shared centimorgans between 4th cousins could be indicative of endogamy, meaning marriages between cousins, etc.)
Some of your 4th cousin matches are not actually 4th cousins
While some of your 4th cousin DNA matches are actually 4th cousins, others are not. Since Ancestry DNA (and any other company) can’t really tell you how you are related to most of your DNA matches, they have to use the amount of shared DNA in order to estimate your relationship. At a 4th cousin level, the range of average shared DNA overlaps with that of other relationships.
For example, the lower range of shared DNA with 3rd cousins is zero, just like with 4th cousins (since there is a 10% chance you will share no DNA with a third cousin). This means that you might only share 20 cMs with a third cousin, and the third cousin will get placed in the 4th cousin category on your match list.
Since placement on this list is based only on shared DNA, you can even find the occasional second cousin on the fourth cousin list. I have more than one half-second cousin once-removed on my fourth cousin list. I share my great-great grandfather as a common ancestor with these second cousins once-removed, so this is a much closer relationship than a fourth cousin.
If you click on any given DNA match in the fourth cousin category, you will notice that it says “estimate relationship: 4th-6th cousin”. This is because some of the people in your 4th cousin match list actually might be more distantly related to you than 4th cousin. They could be 5th cousins, or 6th cousins, or any other relationship between.
This is because it’s also possible to share a higher amount of DNA with a 5th or 6th cousin than average, which would “bump” your DNA match up your list, even though they are pretty distantly related.
Note: It’s also possible to share so little DNA with a 3rd-4th cousin match that they end up on your Distant match list. I know that our DNA match lists get pretty long, but if you find yourself with a little extra time on your hands, it is worth looking at your distant match list. You never know who you will find!
How do I know how my 4th cousin match is related to me?
If I am telling you that your “fourth cousin match” might be a 3rd cousin, or might be a 5th cousin, how in the world are you supposed to know how you are truly related? The easiest way is if you have a solid, well-researched, family tree that goes back 5-7 generations, and your DNA match has the same.
In this case, Ancestry will generally compare your family trees for you, and give you a “Shared Ancestor Hint”.
Other times, you might just spot a common surname and geographic location, meaning that the parent or grandparent of this person is likely your common ancestor (but not always!).
If your DNA match doesn’t have a family tree on Ancestry, then you could consider contacting them politely and asking them if they have a family tree, and if they would like to be in contact to try to determine your relationship. You will need to have a subscription on Ancestry in order to view their tree.
If you use the following link, you will be able to have a two-week free trial on Ancestry, which is great for adding records to your family tree (you don’t need a subscription to build your tree) and really getting access to all of the benefits of Ancestry DNA. I will get a small commission if you use this link, at no extra cost to you whatsoever – it helps me support this website, and thanks 🙂 Ancestry Free Trial
Why are 4th cousin matches useful?
Fourth cousin DNA matches are the most useful to Ancestry DNA users. We usually know enough about our family tree to be able to quickly identify how we are related to our second and third cousins, but fourth cousin matches are how we actually learn about the family ancestry that we don’t already know about.
For people who don’t know much about their extended family tree, fourth cousin matches (and their public family trees) are how we can figure out where our great-great-great grandparents (or more distant) lived.
There have even been stories about people using their fourth cousin matches to identify a biological parent, using only those distant matches and nothing further, though I have not personally used this method for this purpose.
I hope that this post has helped you better understand your cousins in the 4th cousin category on Ancestry. If you have anything that you would like to add, or would like to share your experience with fourth cousin matches on Ancestry, I would love to hear from you in the comments.
Thanks for stopping by!