This article gives simple and clear explanations of the fourth cousin relationship.
I also answer as many questions around fourth cousins as I can think of. Let’s start with the basics!
What Is A Fourth Cousin?
Your Fourth Cousins are children of your parents’ third cousins. You each have a great-grandparent who are first cousins to each other.
You share 3rd great-grandparents with your fourth cousins. You are both five generations away from your common ancestors.
Here is an illustration of the relationship.
One of your great-great-grandparents is a sibling of a great-great-grandparent of your Fourth Cousin.
What is a 3rd great-grandparent?
A 3rd great-grandparent is the same as a great-great-great grandparent. In other words, there are three greats.
We simply word this as “3rd” to avoid repeating all those greats.
Difference With Other Cousins Relationships
Fourth Cousins are more distantly related than third cousins.
If you’d like to see clear diagrams, check out our article that explains third cousins.
But let’s focus on other relationships that can be confused with fourth cousins.
Fourth Cousins are more closely related than fifth cousins. Your child is a fifth cousin to the child of your fourth cousin.
But what about Fourth Cousins once removed? Let’s look at that next.
Fourth Cousin Once Removed
When your Fourth Cousins are “once removed”, this means that they are one generation away from you.
This can be either up a generation (your parents’ generation) or down a generation (your children’s generation).
Children of your fourth cousins
Probably the easiest to understand are the children of your fourth cousins.
These children are your fourth cousins once removed.
Let’s keep going down the tree.
If your fourth cousin once removed had children, these kids would be your fourth cousins twice removed. They are down another generation.
Your parents’ fourth cousins
We’ve looked at the relationship when the removed is down a generation.
But what if it’s up a generation at your parents’ level?
The fourth cousins of your parents are your fourth cousins once removed.
What does 4C1R mean?
You may see articles or charts referring to 4C1R.
4C1R stands for fourth cousin once removed.
Are Fourth Cousins Blood Related?
Your fourth cousins are blood relatives because you share common ancestors i.e. two of your 3rd great-grandparents.
However, if the cousin relationship is through marriage, then you are not blood relatives.
Do Fourth Cousins Share DNA?
Fourth Cousins share amounts of DNA ranging from about 0.07% to 0.5%. The average percentage of shared DNA is about 0.2%.
The number of reported shared centimorgans ranges from zero to 139 cM. The average is about 35 cM.
(% estimates from 23andMe. Cm as reported by DNA Painter).
The reason for the variability is that people inherit different amounts of DNA from common ancestors.
DNA gets shuffled, separated, and recombined as it passes down through generations.
You will receive DNA from your 3rd great-grandparents that your cousins don’t get – and vice versa.
The amount passed down from your 3rd great-grandparents also gets smaller with each generation.
Using DNA websites
If you’ve used one of the big commercial DNA testing services, you may be researching a list of DNA relatives who also tested with the same company.
The websites like Ancestry and 23andMe will give you a prediction of relationships based on the amount of shared DNA.
Be aware that the higher end of the range for fourth cousins will overlap with the lower end of a third cousin. So don’t assume that the labels are correct.
Can Fourth Cousins Not Share DNA?
DNA from specific ancestors gets reduced as it passes through generations.
Is it possible that you don’t share any DNA with a fourth cousin? The answer is yes.
There is a possibility of about 30.7% that you will not share DNA with a fourth cousin.
In other words, about three in ten of your fourth cousins will not share DNA with you.
This gets worse when we move out a generation to fourth cousin once removed. The possibility increases significantly to 52% of not sharing DNA. In other words, that’s a little over half.
These numbers are based on work by a researcher at Cambridge University, Kevin Donnelly. He conducted a study into the probabilities that people don’t share DNA with family members.
How Many Fourth Cousins Do You Have?
Birth rates in your country and community play a big part in predicting the number of fourth cousins.
I wrote an article on using birth rates to calculate the numbers for the U.S., the UK, and Ireland. These were the results based on the 2013 statistics:
- United States: 305 Fourth Cousins
- United Kingdom: 194 Fourth Cousins
- Ireland: 264 Fourth Cousins
I suspect that the U.S. number may vary widely between communities and income levels in the country.
Can you find local birth rate stats for your community? Are you from another country?
Just follow this article where I calculate how many cousins Irish people have. You can work out your own predictions using the same formula.
Are Fourth Cousins Really Family?
Are fourth cousins part of close family? Extended family? Distant family?
This depends on the context. I’ll look at this from a legal context, a genetic context, and normal conversations.
Legal context
In many jurisdictions, fourth cousins are not considered immediate family in legal matters.
For example, if your employment has restrictions that mention immediate family then this probably does not include fourth cousins.
However, you should always check with the specific department (or state authority).
Day-to-day conversation
Because the common ancestors go back so far, many of us have never met fourth cousins. Or at least, we haven’t been aware that acquaintances are colleagues fall into this bracket!
For that reason, they are considered distant family in normal conversation.
DNA websites
If you’ve tested with a commercial DNA site, you may be researching your DNA relatives.
Some of the websites put a label of “distant relatives” on many people in your list of DNA matches.
My fourth cousins on Ancestry.com are under the “distant relatives” label. In contrast, second cousins are labeled as “close family”.
Can You Marry Your Fourth Cousin?
Every state in the U.S. allows marriage between fourth cousins.
Most countries in the world allow fourth cousins to marry.
Some American states and other countries do have restrictions on first cousin marriages.
However, fourth cousin relationships are so distant that there are no legal impediments against marriage.
Can Fourth Cousins Get Married In A Catholic Church?
You may be aware of restrictions and hurdles for first cousins to get a Catholic wedding.
Fourth cousins can marry in a Catholic church without any restrictions. There is no need to get permission or dispensation from the church hierarchy.
The reason is the way that Canon Law rates the degree of relatedness.
Canon law and fourth cousins
Canon law is based on counting the number of generations away from the common ancestors for the two potential spouses.
The common ancestors of you and your future third-cousin spouse are your 3rd great-grandparents.
You are both five generations away from your common ancestors. We add those numbers together to come up with ten degrees.
This is called ten degrees of consanguinity. Don’t get too caught up with the terminology.
The point is that Canon Law used to prohibit marriages up to the sixth degree. This was more recently relaxed to the fourth degree (first cousins).
Fourth cousins have always fallen outside the restrictions.
Frequently Asked Questions
Do fourth cousins share the same blood?
Fourth Cousins are blood-related and are considered to share the same blood as their common ancestors, their 3rd great-grandparents.
If you want to know how much DNA they share, check out an earlier section in this article.
How are third and fourth cousins related?
Your third and fourth cousins are one generation away from each other.
One of your fourth cousin’s parents is a third cousin to one of your parents.
