Understanding genealogy and family relationships can sometimes feel like a complex puzzle. Terms like “first cousin once removed” can leave people stumped.

The key to deciphering these terms is understanding generational differences. A cousin is referred to as being once-removed or twice-removed based on how many generations are between you and the person you describe.

What is a first cousin?

With DNA testing, Facebook, and online family trees bringing us new cousins daily, it’s essential to understand what it means to be first cousins once removed. Cousin relationships are defined by degrees of separation from a common ancestor, and this article will help you distinguish between different types of cousins based on the number of generations between you and your cousin.

To be considered a first cousin, you must share one set of grandparents (maternal or paternal). The offspring of those grandparents are your aunts and uncles. When those siblings have children, the grandchildren are your first cousins. If those grandchildren have children of their own, the grandchildren are your first cousins once removed. Each generation that separates you from your cousin adds one to the cousin designation, so your first cousin once removed is your first cousin’s child or grandchild, and your second cousin once removed is their child or grandchild, etc.

The number of generations between you and your cousin may seem like a lot. Still, the good news is that most commercial ancestry tests will accurately detect this relationship up to your fourth or fifth cousin, so it’s usually easy to figure out how you are related to your cousin once or twice removed, or even thrice or more removed.

What is a second cousin?

A second cousin shares one or more of your common grandparents. They may also share one or more of your great-grandparents, in which case they are a 1st cousin once removed. Generally, you will share DNA between 3 and 592 cm (on average) with your second cousin.

The labeling of cousins is based on the number of generations between your shared ancestor and the two cousins. The number of “removes” identifies how far apart you are in the generation chart. For example, your mother’s first cousin’s children are her first cousins, and her grandchildren are her first cousins once removed.

As the generations increase, the relationships become more distant, and the names are shortened. The number of generations between you and your cousins determines the degree of relationship or cousinhood.

Count how many “greats” are in the common ancestor’s title to calculate the relationship and add 1. For example, your maternal aunt’s grandson is her first cousin once removed because he has three “greats” in common with you and one of the shared great-grandparents. The same applies if the child of your first cousin is their first cousin once removed. This makes sense because they have the same great-grandparents but are separated by a single generation.

What is a third cousin?

Understanding the relationships between cousins is essential, especially if you’re using DNA to research your family history. Knowing the exact degrees of cousin-ness will help you determine how much DNA you may or may not share with someone. It will also allow you to identify potential genetic matches for disease-related studies.

A first cousin once removed (C1R) is a relative who shares a common ancestor with you but is one generation older than you. If that cousin has children, their child is your first cousin once removed’s grandchild. A second cousin, once removed, is a relative with one or more of your great-grandparents. If that cousin has a child, their child is your second cousin once removed’s grandson or granddaughter.

Third cousins are those in the same generation as you or your children. If a first cousin once removed has a child, you are a third cousin to that child. A second cousin once removed is a cousin that has two or more of the same great-grandparents. If that second cousin has a child, you are a second cousin to their son or daughter. Third cousins on either side of your family share about 1-2% of their DNA. However, that amount could be significantly lower if they are from distant family tree branches.

What is a fourth cousin?

A fourth cousin is related to you through a common ancestor who is your three or more great-grandparents. This relative can either be your parent’s first cousin or the child of your first cousin. In both cases, the relationship is a fourth cousin once removed.

The concept of cousins, once removed, can be complicated because it’s not always clear whether your relation is a generation above you or below you. You can only determine this by counting the generations between you and your cousin.

If your first cousin’s child is a generation above you, they are your first cousin once removed. However, if their child is a generation below you, they are your first cousin twice removed.

DNA testing to identify family relationships can be extremely helpful when building your genealogical tree. Depending on the type of test you have taken (autosomal, YDNA, or mitochondrial), you may be able to see genetic relationships up to five or six degrees away.


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