This article gives simple and clear explanations of where first cousins fit in your family tree.
I also answer some common questions around first cousin relationships, like whether you can get married.
Let’s start with the basics!
Table of Contents
What Is A First Cousin?
Your first cousins are the children of your aunts and uncles.
Here is an illustration of the relationship. Do your parents have brothers and sisters? Their children are your first cousins.
You and your first cousins are of the same generation. You share common grandparents. So your common ancestors go back two generations.
What Is A Half Cousin?
If your parents have half-siblings then their children are your half cousins.
Your most recent ancestor is one grandparent as opposed to two grandparents.
Here’s an example scenario. Your grandfather married twice and your father has a half-brother through the earlier marriage. This man is your half-uncle.
The children of your half-uncle are your half first cousins. If that’s confusing, the illustrated picture below should make it clear. Note that your grandmother is not in this branch of the family tree (she will be in other branches).
It’s rare in English-speaking cultures to reference the “half” half-cousin relationship. Most of us will simply call them our cousins.
It only becomes important in some legal scenarios such as inheritance.
We share less DNA with half-cousins than with full cousins. This is because we have one most recent common ancestor instead of two.
What’s The Difference Between First Cousins And Second Cousins?
First cousins are a closer relationship to you than your second cousins.
This is best described in the picture below. On the left, you share grandparents with your first cousin. In other words, you are two generations from your common ancestors.
The picture on the right shows you and your second cousin at the bottom of the tree. You share great-grandparents where are three generations away.
We have a separate article answering a range of questions on second cousins.
First Cousins Versus First Cousins Once Removed
People do get confused between these two relationships. What does “once removed” mean anyway?
We’ve written a separate article on what first cousins once removed means. It’ll show you several possible relationships in a family tree that fall under the “once removed” category.
The Name Of The Relationship Works Both Ways
When you are first cousin to family members, they are also first cousin to you.
A lot of family relationships don’t work like that. You are niece to your aunt, but of course, your aunt is not your niece.
But “first cousin” is the same term for the relationship from both sides.
What does 1C mean?
You may see articles or charts referring to 1C.
1C1R stands for first cousin (1st Cousin).
Are First Cousins Blood Related?
Your first cousin is a blood relative when you share common ancestors.
If the cousin relationship is through marriage, then you are not blood relatives.
Let’s take an example to explain. Let’s say that your uncle married a woman who had a child from a previous relationship.
Personally, I would call this child my cousin. (Some cultures may not).
However, we are not blood related.
Do First Cousins Share DNA?
First cousins share amounts of DNA ranging from about 7.3% to 13.8%. The average percentage of shared DNA is about 12.5%.
This is about 400 to 1,400 centimorgans of shared DNA.
(% 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. You will receive sections of DNA from your grandparents that your cousins don’t get – and vice versa.
The amount passed down from your 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 first cousins will overlap with the lower end of half-siblings and aunts or uncles.
If you need more help with understanding the relationships on these services, check out these overviews:
- How to research your Ancestry DNA matches
- How to research your 23andMe DNA relatives
Can first cousins not share DNA?
I mentioned that the DNA from an ancestor gets reduced as it passes through generations.
Is it possible that it could all disappear within two generations? The answer is no. First cousins will always share some DNA.
This was demonstrated by a researcher at Cambridge University. Kevin Donnelly conducted a study into the probabilities that people don’t share DNA with family members.
There will be enough DNA to meet the thresholds of the major DNA testing sites.
In other words, if you and your first cousin have both tested on Ancestry.com or 23andMe, then you should be able to see each other listed as DNA relatives.
How Many First Cousins Can You Have?
One of my mother’s aunts had eleven children. There are 32 first cousins in that family branch alone.
This wasn’t too unusual for Ireland in the 1940s and 1950s. However, the Irish birth rate has fallen in recent decades. I have far fewer first cousins than my mother (but lots of second cousins).
The purpose of this anecdote is to show that birth rates in your country and community play a big part in predicting the number of first cousins.
I wrote an article on using birth rates to calculate the numbers. Below are the counts for the United States, the United Kingdom, and Ireland.
I’m showing the numbers from first cousin out to 8th cousin. Specifically, Americans tend to have 4.4 first cousins, British people have 3.5 first cousins and Irish people have 4.1 first cousins.
If you’re from somewhere else, just find recent birth rate statistics for your country and follow this article where I calculate the number of cousins Irish people have.
Do First Cousins Count As Close 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, including the United States, first cousins are often considered close family in legal matters.
For example, if your employment has restrictions or rules that mention close family then this probably includes first cousins. This could apply to providing commercial contracts or to getting permission to attend funerals.
However, you should always check with the specific department (or state authority). The interpretation may vary between organizations.
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 “close family” on some people in your list of relatives.
For example, Ancestry.com includes first cousins in their close family category. You can read more on Ancestry’s relationship labels here.
Normal conversation
You’re wondering why you didn’t get a wedding invitation, and the answer is that only “close family” were invited. What does that mean?
You see “close family only” on a funeral notice. Should you attend?
This depends on the culture and community. First cousins may be a stretch!
But here’s a hint that may help. “Immediate family” does not usually include first cousins. So, if people are using the term “close family” instead, then that may expand to the children of aunts and uncles.
Do First Cousins Look Alike?
Anecdotally, I can tell you that I know first cousins who are often mistaken as brothers. They resemble each other more closely than they look like their own siblings.
However, I also know plenty of first cousins who bear no family resemblance.
There is no way of predicting whether first cousins will look alike or not. They both inherit a percentage of DNA from two grandparents – but they may not inherit the same chromosomes or regions of DNA.
As a theoretical example, let’s say that an area of DNA that influences hair color. Some first cousins may receive this section unchanged from one grandparent. Others may receive it from a different grandparent.
Due to the random nature of inheritance, there is no way of predicting who gets what.
What Degree Is A First Cousin?
You may see references in legal or genealogical texts about the degrees of “kinship” between cousins. You may also see terms like “collaterals within the fourth degree”.
Let’s explain these terms clearly. A “collateral” is simply a relative who isn’t in your direct line. This includes your uncle or aunt, or any of your cousins.
But what do “degrees” mean? This is a measure of the distance between you and your cousin. It’s a very simple count of the number of people between you and your common ancestors.
In this case, the common ancestors are your grandparents – who are also the grandparents of your first cousin.
There are two degrees (or hops) between you and your grandparents. The same applies to your first cousin. You simply add these counts together!
A picture tells a thousand words! This diagram should make it clear.
What degree of relationship is a first cousin?
First cousins are at the fourth degree of relationship.They are collaterals within the fourth degree.
Can You Marry Your First Cousin?
Nearly half of states in the United States do not allow marriages between first cousins. At the time of writing, these were:
- Alaska, Arkansas
- Delaware
- Idaho, Iowa
- Kansas, Kentucky
- Louisiana
- Michigan, Mississippi, Missouri, Montana
- Nebraska, New Hampshire, North Dakota
- Ohio, Oklahoma, Oregon
- South Dakota
- Texas
- Washington, West Virginia, Wyoming
State laws do change over time, so you should double-check with your state of interest.
Some more states only allow first cousin marriage when some conditions are met.
For example, the woman may be required to be past the age of child-bearing. This age differs in different states.
Exceptions may also be made for younger people if infertility can be proven.
Outside the U.S.
It may surprise you to learn that the United States is somewhat unusual in having these restrictions. The U.S. is joined by China and North Korea with prohibitions.
Many other countries have no restrictions on first cousins. It’s legal in most European countries. Here are just some of the countries where first cousin marriage is legal:
- Canada
- United Kingdom
- Ireland
- Australia
- France
- Japan
- India
There are many more on the list.
Can First Cousins Get Married In A Catholic Church?
Even though it may be perfectly legal to marry your first cousin, there are other hurdles if you want to a Roman Catholic wedding.
In general, the Catholic Church isn’t keen on first cousin marriages. But they do have a procedure to get permission for a church marriage.
First cousins must get permission from the local Bishop in order to get married in a Catholic church. I’ll explain why in the next section.
You may see reference in older articles and books about having to get permission from the Vatican. Don’t worry!
The changes to Canon Law in 1983 relaxed this. Your local bishop can provide the dispensation.
Are you sure you are first cousins?
But I want to say straight away that make sure you really are “first” cousins.
Are you actually first cousins once removed? Then you usually won’t have a problem.
Read our article on first cousins once removed which explains the relationship and what it means for church marriages.
So let’s get into the details of Canon law.
Canon Law and first cousins
Canon Law is quite specific on the cousin relationship, but it doesn’t actually mention the term “first cousin”.
Instead, they talk about degrees of consanguinity. Consanguinity simply means blood-related.
I’ve already looked at “degrees” in an earlier section. There’s a diagram that explains exactly how may degrees are between you and your first cousins.
The answer is that first cousins are at four degrees of consanguinity. Relatives at this level must get dispensation from a local bishop to have a church marriage.
That is a little daunting. However, your local priest should help you with the application process.
What about more distant cousins?
I described half first cousins earlier in the article.
This adds one extra degree to the count, which brings it out of the prohibited category i.e. there are no restrictions.
Frequently Asked Questions
Do first cousins share the same blood?
First cousins are blood-related and are considered to share the same blood as their common ancestors.
If you want to know how much DNA they share, check out an earlier section in this article.
Do first cousins share the same grandparents?
First cousins share the same grandparents. One of your parents is a full sibling of the parent of your first cousin.
