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What is a Fourth Cousin?

What is a fourth cousin? How many fourth cousins does the average person have? In this post, you’ll learn the answer to these questions, as well as:

  • What is a fourth cousin once-removed?
  • Whether fourth cousins share DNA
  • What is a half-fourth cousin?
  • Are fourth cousins blood related?
Image describing the subject of the article, "What is a Fourth Cousin?"

Most people grow up knowing only their first and second cousins. Only rarely will someone know a third or fourth cousin personally and know how they are related.

So, it is understandable that the exact cousin relationship between these two cousin types is a bit confusion. My goal is that this post clears everything up for you.

What is a fourth cousin?

A fourth cousin is a person who shares one set of great-great-great grandparents with you. Another way to think about it is that a fourth cousin is descended from a sibling of your great-great grandparent.

In order to be a fourth cousin without any generations “removed”, you both must be the same number of generations descended from your great-great-great grandparent. You and your fourth cousin must both be the great-great-great grandchildren of that common ancestor.

The other bit of information that is important to explain in more detail is that you also must be descended from different children of that 3rd great-grandparent. If you and your cousin are both descended from the same child of the ancestor, then you might be third cousins.

Fourth cousins are relatives descended from our common ancestor on collateral lines of our family tree.

Fourth cousins share which grandparent?

To put it simply, fourth cousins share at least one great-great-great grandparent. This ancestor is also known as the most recent common ancestor.

The image below shows an example of fourth cousins. The “ancestors” are Abel and Maria. Two of their children are displayed in the example, and you can see how the descendants of their children are related.

A chart depicting the answer to "what is a fourth cousin?"  This includes an example of two fourth cousins descended from Abel and Maria through two different descending lines of their offspring
In this image, you can see what is a fourth cousin. The fourth cousins in this example are great-great-great grandchildren of Abel and Maria, descended from two of their children.

To explain the graphic even further:

  • The children of Abel and Maria are siblings
  • The grandchildren of Abel and Maria are first cousins
  • The great-grandchildren of Abel and Maria are second cousins
  • The great-great grandchildren of Abel and Maria are third cousins
  • The great-great-great grandchildren of Abel and Maria are fourth cousins

As long as the descendants of Abel and Maria are the same number of generations removed from the common ancestor (in the case of fourth cousins, five generations), they are fourth cousins.

If Abel and Maria’s great-great-great grandchild would like to know how to describe their exact relationship to a cousin who is of a different generation (i.e. Abel and Maria’s great-great grandchild), then they will have to read the next section about fourth cousins once-removed.

If you have a fourth cousin who is descended from a sibling of your great-great grandparent who married a sibling of a great-great grandparent of a different line of your family, then you have a double-fourth cousin. You can read more about double-fourth cousins here:

What is a fourth cousin once-removed?

A fourth cousin once-removed is the child of your fourth cousin or the fourth cousin of your parent (i.e. you are the child of the fourth cousin).

When two cousins share the same common ancestor but don’t share the same number of generations in descent from said ancestor, we use the term “removed“.

The person who is the closest to the common ancestor sets the cousin-relationship type (i.e. first/second/third/fourth cousin) and then the “removed” is calculated from that’s person’s generation level to the other cousin.

For example, in the case of fourth-cousin once-removed, we know that a fourth cousin is a great-great-great grandchild of the common ancestor. If the other cousin is the great-great-great-great grandchild, then there is one generation difference between them and they are fourth cousins once-removed.

What is a fourth cousin twice-removed?

If your relative is grandchild of a fourth cousin, then they are fourth cousins twice-removed. The common ancestor shared is still your great-great-great grandparent, but that ancestor is the great-great-great-great-great grandparent of your fourth-cousin twice-removed.

If there are more than two generations between the cousins, then you just keep counting, adding the number of generations removed. For example, a great-grandchild of your 4th cousin is a fourth-cousin three-times removed.

What is a half-fourth cousin?

As you now know, a fourth cousin is someone that is descended from a full sibling of your great-great grandparent. You share both great-great-great grandparents with your fourth cousin.

A half-fourth cousin is a person who is descended from your great-great grandparent’s half-sibling. In other words, you only share one great-great-great grandparent in common.

For some people researching their family tree, distinguishing between full and half-fourth cousins is very important. This is especially true when it comes to those who use DNA to research their family trees.

Half-fourth cousins will share less DNA, on average, as full fourth cousins.

How many fourth cousins do I have?

Any given person might have 940-1500 4th cousins, or more. However, the actual number of relatives that you have on any generation depends on lots of variables.

For example, if all of your great-great-great grandparents had lots of kids, and all of those kids survived to adulthood and had lots of kids themselves, then you might have more 4th cousins than the average person.

Alternatively, if your ancestors and their descendants were affected by natural disasters, wars, famines, and illness, you might have fewer fourth cousins than average.

It might be possible to track down all of your fourth cousins, but it would likely take years of work. Plus, if you have ancestors that lived in other countries 150 years ago, your 4th cousins might be located all over the world.

Are fourth cousins blood related?

Will 4th cousins be blood related, or share DNA? You will only share genes with about 50% of your many fourth cousins.

This is because we don’t actually share DNA with all of our relatives. Furthermore, 4th cousins are considered to be distant cousins.

The amount of DNA that you will share with a fourth cousin with whom you do share DNA is will be small. The 4th cousin DNA percentage shared is .19%, which works out to about 14 centimorgans.

If you have 940 4th cousins and all of them took a DNA test, statistics tell us that only about 470 of those cousins would show up as DNA matches to you. In other words you are related genealogically to all of your fourth cousins but you might not share DNA.

Furthermore, if your fourth cousin is a half-fourth cousin, there is a higher chance that you will not share any identical DNA.

A true 4th cousin can be different than a fourth cousin DNA match. If you want to learn about fourth cousin DNA matches on sites such as Ancestry DNA, click here:

What is a Fourth Cousin Pinterest Image


I hope that this post helped you understand more about fourth cousins, how many fourth cousins you have, and whether fourth cousins are always “blood related” (whether they share DNA).

While it’s not very common to grow up knowing any of your fourth cousins personally, it is not impossible! Other times, we get to know our fourth cousins by accident through our genealogy research.

If you have any questions about something that you read in this post, or if you would like to share your own experience finding fourth cousins, I would love to hear from you in the discussion below

Thanks for stopping by today!

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