Cousin Relationships

Calculating cousin relationships can be a bit tricky. When you extend out beyond first cousins, you can get into a situation where you have to calculate the number of generations between you and your cousin. In this article, we will show you how to calculate your cousin relationships with different family members.

Make sure that you also try our cousin relationships calculator. It is a great way to see how many generations you have between you and your cousin.

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Our close blood family connections are very easy to understand and far from complex. Our links to our grandparents, parents, uncles, aunts, sisters, brothers, sons and daughters are very basic. Barring any complex family secrets, we know where our relationship stands with these close members of our families.

It isn’t until we start using the word cousin that we begin to stumble over how we are related to someone. We catch ourselves saying things like “oh that’s great Aunt Edna’s daughter” instead of referring to their actual relationship with you, which is a first cousin once removed.

Maybe it's time to try and explain cousin relationships a little so that we can feel more comfortable in knowing how we are related.

The Easy Cousin

It’s best to start with the easiest cousin connection we likely have, the first cousin. This connection is simple and if we have aunts or uncles we may all know some first cousins. Quite simply, a first cousin is the child of our aunt or uncle. They are also our parents' nieces or nephews.

When Are They Just Cousins?

One important rule to remember is that when the term cousin is used without any other term except maybe a number, this means they are in the same generation as you.

This basically means that you are the same number of generations separated from your shared ancestors. This may be your grandparents, great grandparents or however many generations back you could go.

These relationships are first, second, third cousins etc, and the numbering carries on adding each successive generation.

What Does Removed mean?

Now we come to the more complicated terms. What exactly does the term "removed" refer to? This actually isn’t too complicated either as it merely indicates that the relative is a cousin of a different generation. As an example, if your first cousin has a child then that child is your first cousin once removed.

The reason that the child is once removed is that they are one generation further away from your shared ancestor. So, whereas the shared ancestors are your grandparents, to your first cousin once removed they are great grandparents.

This works in both directions generationally because, as an example, your grandparents' first cousin would be your first cousin twice removed. The removal refers to the fact that they are two generations back from your generation.

The greater the separation of generations between your cousin and your mutual ancestors the higher the removed number would be.

Calculating Cousin Relationships

In order to quickly determine your relationship with a cousin there are simple ways to remember how to figure this out. Firstly, for cousins in the same generation:

  • Start by determining who your closest shared ancestors are
  • Remember that first cousins share the same grandparents
  • Add one for every successive generation you go back in terms of grandparents. For example, if you share great grandparents you are second cousins, if it's great-great-grandparents then you are third cousins and so on.

Next, we tackle cousins who are not in the same generation.

  • Start by determining which cousin has the smallest generational gap between your common ancestors. If this were to be a great-great-great grandchild then your cousin match is fourth cousins.
  • Then determine how many generations separate you and your cousin either forward or backwards in the generational count. If this is three generations then you would be fourth cousins three times removed

Cousin Matches and DNA

If you have tested with Ancestry or 23andMe you probably have an extensive list of third, fourth and fifth cousins. The question is how accurate is the relationship estimate? In terms of close blood relationships, DNA testing is largely accurate and easy to understand. When we get further away in relationships it can become more complicated.

Even beginning at the first cousin level the amount of shared DNA is generally not extensive. In terms of shared DNA percentage, a first cousin relationship is similar to a great grandparent. This means on average you might share 12.5% of your DNA. However, this is not a fixed amount and the real number can vary between 4-23%.

This wide potential gap in shared DNA means that a first cousin could potentially test closer to a second cousin level of DNA. This obviously means that second, third and fourth cousins may also test inaccurately or may not share any DNA with you at all.

When it comes to distant cousin DNA matches you really need to support them with documentation for them to be accurate. If they can be traced back to the correct shared ancestor through records and the DNA match falls within the right levels then the relationship is confirmed.

Other Cousin Complications

There are some other interesting cousin connections that upset the proverbial apple cart. One such connection is the rare double cousin. When siblings marry the siblings of another family and both couples have children, the resulting offspring are double first cousins.

Genetically double cousins have received more of the same DNA because their parents married into the same families. The DNA relationship is closer to that of a half-sibling than a first cousin. As such this could make for some odd DNA results.

There are also half cousins which is an interesting term. This occurs when the children of your shared ancestor, from whom you and your cousin descend, were only half-siblings. Because they only shared the DNA of one of your shared ancestors you and your half-cousin share less DNA than you would if you were full cousins.

Final Thought

As confusing as cousin relationships can be, they are not impossible to figure out as long as you can trace your lines back to your common ancestor. The rules are simple and all you have to do is do the relationship math.

Neil Edwards

Neil Edwards

Genealogist and family-tree research specialist

Neil was born in Shropshire, England surrounded by centuries of living history. His interest in the past has been a lifelong passion leading to undergraduate degrees in both Economic History & Geography and History & Politics.

This interest in history quickly translated to family history when he moved to the U.S. in 2010. It was here that he began working on his own family tree as well as that of his American wife. That research allowed him to gain a wealth of experience working with both U.S. and European genealogical documents and studying their best uses in researching family history.

Following 9 years of honing his genealogical research skills, Neil was proud to have earned a certificate in Genealogical Research from Boston University in late 2019. Neil also took part in the research process for a Duke University study into the families of 19th Century UK Members of Parliament.

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