Cousin Relationship Calculator
Name the relationship between two people from how many generations each is from a shared ancestor, including cousin degree, removal and half relationships.
Counting to the common ancestor
Every blood relationship can be described by two numbers: how many generations each person is from the nearest ancestor they share. Count 1 for a parent, 2 for a grandparent, 3 for a great-grandparent. Siblings are 1 and 1; first cousins share grandparents, 2 and 2; second cousins share great-grandparents, 3 and 3. The cousin degree is the smaller number minus one, and the removal is the difference between the two numbers. If A’s great-grandparents are B’s great-great-grandparents, A is 3 generations from them and B is 4: they are second cousins once removed, because the smaller number is 3, giving degree 2, and the difference is 1.
What “removed” means
“Removed” is the most misunderstood word in family history. It does not mean distance by marriage or a cousin who has moved away. It means the two people are in different generations relative to the shared ancestor. Your first cousin’s child is your first cousin once removed, and so is your parent’s first cousin: in both cases one of you is 2 generations from the shared grandparents and the other 3. Your first cousin’s grandchild is your first cousin twice removed. A common misconception is to call a cousin’s child a “second cousin”; second cousins are the children of first cousins, related to each other, not to the first cousins’ generation.
Aunts, nieces and the great-grand problem
When one person is 1 generation from the ancestor, the relationship is aunt, uncle, niece or nephew rather than cousin. Your parent’s sibling is your aunt or uncle, 1 and 2. Your grandparent’s sibling, 1 and 3, is your great-aunt or great-uncle, which some genealogists prefer to call a grand-aunt or grand-uncle, since that person is in your grandparents’ generation. Your great-grandparent’s sibling, 1 and 4, is a great-great-aunt or great-grand-aunt. When one person is 0 generations from the ancestor, they are that ancestor: parent, grandparent, great-grandparent and so on.
Half relationships and DNA
Relationships through a couple are full; relationships through only one shared person, such as the children of half-siblings, are half. The name is the same with “half” in front, but the expected DNA halves. On average, first cousins share 12.5% of their autosomal DNA, about 850 centimorgans, and half first cousins 6.25%, about 425 cM. Second cousins once removed share on average 1.56%, about 106 cM, but the actual amount varies widely, and some distant cousins share no detectable DNA at all even though they are genealogically related.
How to use it
- Identify the nearest ancestor or ancestral couple the two people share.
- Count the generations from person A up to that ancestor, and from person B.
- Choose whether they descend from a couple or from only one person.
- Read the relationship in both directions and the expected shared DNA.
Questions from the record office
What is a second cousin once removed?
Either the child of your second cousin or the second cousin of one of your parents. In both cases, one person is 3 generations from the shared ancestors, the great-grandparents, and the other is 4. The cousin degree comes from the smaller number and the removal from the difference.
What does "once removed" mean?
That the two cousins are one generation apart relative to their common ancestor. Your first cousin’s child is your first cousin once removed, and so is your parent’s first cousin. Twice removed means two generations apart, such as your first cousin’s grandchild.
Is my cousin's child my second cousin?
No. Your cousin’s child is your first cousin once removed. Second cousins are people whose parents are first cousins; your child and your first cousin’s child are second cousins to each other.
How much DNA do first cousins share?
On average about 12.5% of their autosomal DNA, roughly 850 centimorgans, because they share two grandparents. In practice, first cousins commonly share anywhere from about 400 to 1,400 cM. Half first cousins, who share one grandparent, average about 425 cM.
Disclaimer: Genealogy results apply published conventions and inheritance averages to the values you enter. They are not proof of a relationship, parentage or descent, and not legal, medical or genetic advice. Several relationships share each DNA figure, and calendars and spellings varied by place and time: check every conclusion against original records, and consider the privacy of living relatives before sharing it.