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Confused by all those cousins-once-removed? Use this handy relationship calculator to get things straight.

What exactly are cousins-once-removed? The charts below will help you calculate these types of blood relationships

Blood relationships are determined by calculating the shared ancestry of two individuals. That is determined by counting the generations from each individual to the closest common ancestor; siblings share a parent, first cousins share a grandparent and so on.

In contrast, consanguinity usually refers to a calculation of shared ancestry that includes all common ancestors.

Most cultures and languages have special terms to describe close blood relationships such as mother, father, parent, child, sibling, aunt, uncle, niece, nephew, and cousin.

Those relationships are well-understood and it is not necessary to actually count the generations to know the relationship. Terms in common use for more distant relationships are generally less precise. In English, people who share an ancestor more than two generations back may simply be called cousins or distant cousins. Many people, for example, could not express the precise relationship between the Subject and the Cousin's Child as shown in the chart below:
Here's how to calculate the relationship.

The closest common ancestor is the Grandparent of the Subject (two generations) who is also the great-grandparent of the Cousin's Child (three generations).

When the number of generations to the common ancestor is not the same for both the subject and the relative, the first part of the relationship term is determined by the lesser of the two distances to the common ancestor. In this case, that is two, and so the first part of the relationship is "First Cousin". The second part of the relationship term is determined by the difference between the two distances to the common ancestor. In this case, that is one (three minus two), and so the relationship term is First Cousin, Once Removed.

After reading the above, one might be tempted to call a niece or nephew a "sibling once removed", but I don't recommend it!

Please note that a descendant of your first cousin can never be a second cousin to you. The number of times removed increases with each generation. As shown below, a second cousin is related through one of your great grandparents.

The chart shows an interesting characteristic of relationship terms. Most of the terms for near relations are not reciprocal: mothers and fathers have daughters and sons, aunts and uncles have nieces and nephews. The most common reciprocal term is cousin: cousins have cousins. Note that "1st Cousin Once Removed" appears twice in the chart. The child of your 1st cousin and the child of your great aunt or uncle are both your first cousin once removed. Note that the number of generations difference is the same:

The relationship from a child of your great aunt or great uncle to you is the same as the relationship from you to a child of your 1st cousin. Return to Home Page from cousins-once-removed

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