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Cousin calculator
Is your cousin's daughter your second cousin or your first cousin once removed? Find the closest ancestor two people share, say how each descends from them, and the calculator names the relationship — in both directions.
Work out a relationship
Tip: the common ancestor is the closest person (or couple) both people descend from. For you and a first cousin, that is your shared grandparents — so you are each a "grandchild".
Cousin chart
Rows show Person A's generation below the common ancestor, columns show Person B's. Each cell says what Person B is to Person A. Click any cell to load it into the calculator.
How the cousin rule works
Count how many generations each person is below the common ancestor: a child is 1, a grandchild 2, a great-grandchild 3, and so on. Then:
- Cousin degree = the smaller number minus 1. Two grandchildren (2 and 2) are first cousins; two great-grandchildren (3 and 3) are second cousins.
- Times removed = the difference between the two numbers. A grandchild (2) and a great-grandchild (3) are first cousins once removed; 2 and 4 are first cousins twice removed.
- If either number is 0, one person is the ancestor — a direct line (parent, grandparent…).
- If the smaller number is 1, one person is a child of the ancestor, so they are siblings, or aunt/uncle and niece/nephew.
Worked examples
| Question | Generations | Answer |
|---|---|---|
| My first cousin's child | 2 and 3 | First cousin once removed |
| My parent's first cousin | 3 and 2 | First cousin once removed |
| My child and my first cousin's child | 3 and 3 | Second cousins |
| My grandparent's sister | 3 and 1 | Great-aunt (grand-aunt) |
| My second cousin's grandchild | 3 and 5 | Second cousin twice removed |
| My father's half-brother's son | 2 and 2, half | Half first cousin |
What "once removed" really means
"Removed" only means different generations. Your first cousin's child is one generation below you, so they are your first cousin once removed. Your parent's first cousin is one generation above you — also your first cousin once removed. The term works in both directions, which is why the relationship is the same whichever person you ask.
A common mix-up: your first cousin's child is not your second cousin. They are a second cousin to your children, because your children and they are in the same generation.
Half cousins and double cousins
Half relations share only one ancestor instead of a couple — for example, children of half-siblings are half first cousins. They share, on average, half as much DNA as full cousins of the same degree.
Double cousins are related through both sides of the family, typically when two siblings from one family marry two siblings from another. Double first cousins share both sets of grandparents and, on average, about 25% of their DNA — as much as half-siblings. Run the calculator once for each line and add the DNA figures together.
How much DNA do relatives share?
The percentages above are long-run averages for autosomal DNA. Because DNA is inherited in random chunks, real pairs vary: two first cousins can share anywhere from about 7% to 19%, and very distant cousins may share no detectable DNA at all. Treat DNA-test predictions as ranges, and confirm them with records.
Frequently asked questions
What relation is my cousin's child to me?
Your first cousin's child is your first cousin once removed. To your children, the same person is a second cousin.
What does "once removed" mean?
The two cousins are one generation apart. Twice removed means two generations apart, and so on.
What is a second cousin?
Second cousins share great-grandparents but not grandparents. They are the children of two first cousins.
Is a great-aunt the same as a grand-aunt?
Yes. Your grandparent's sister is a great-aunt in everyday English and a grand-aunt to many genealogists. Read more in family relationship names explained.
How much DNA do first cousins share?
On average about 12.5%, though the real figure for any pair varies, typically between roughly 7% and 19%.
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