What is a first cousin?
Short answerYour first cousin is the child of your aunt or uncle: you share a set of grandparents. It works the same both ways: you are their first cousin too. Full first cousins share about 12.5% of their DNA on average.
The family line, drawn out
Follow the highlighted line from you up to the shared ancestor and down to them.
How to work it out
- Find the nearest ancestor you share: your grandparent.
- Count the generations from each of you up to that ancestor: 2 for one, 2 for the other.
- Take the smaller number and subtract one: 2 − 1 = 1, so they are first cousins.
- The difference between the two numbers is how many times removed: 2 − 2 = 0 (not removed).
Cousins are only “removed” when they belong to different generations. Two people in the same generation are never removed, whatever their ages.
Their family and yours
Relationships shift by one step for each generation. Here is how the people around them relate to you:
| Their child | first cousin once removed |
| Their parent on the shared line | aunt or uncle |
| Your child sees them as your child’s | first cousin once removed |
| Your parent sees them as your parent’s | niece or nephew |
| What they call you | first cousin |
Shared DNA
On average, full first cousins share about 12.5% of their DNA. That figure is the expected value: it halves with every generation of separation, and real amounts vary from person to person. A half relationship (through only one shared ancestor instead of a couple) shares about half as much: 6.25%.
Let Family Trees name it for you
In Family Trees, open anyone’s page to see how they are related to you in plain words, or choose any two people under How are they related?. The app counts the shortest blood line through birth and adoptive parents, names step, foster and in-law relations too, and uses exactly the words on this page. It’s free for a family of up to 100 people. You can also try the relationship calculator here.
Questions
What is a first cousin?
Your first cousin is the child of your aunt or uncle: you share a set of grandparents. It works the same both ways: you are their first cousin too.
How much DNA do you share with a first cousin?
About 12.5% on average. Each generation of separation halves the expected amount, and individual results vary.
What is my first cousin’s child to me?
Your first cousin once removed.