What is a fourth cousin?
Short answerYour fourth cousin is the child of your parent’s third cousin: you share a set of 3rd great-grandparents. It works the same both ways: you are their fourth cousin too. Full fourth cousins share about 0.2% 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 3rd great-grandparent.
- Count the generations from each of you up to that ancestor: 5 for one, 5 for the other.
- Take the smaller number and subtract one: 5 − 1 = 4, so they are fourth cousins.
- The difference between the two numbers is how many times removed: 5 − 5 = 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 | fourth cousin once removed |
| Their parent on the shared line | third cousin once removed |
| Your child sees them as your child’s | fourth cousin once removed |
| Your parent sees them as your parent’s | third cousin once removed |
| What they call you | fourth cousin |
Shared DNA
On average, full fourth cousins share about 0.2% of their DNA. That figure is the expected value: it halves with every generation of separation, and real amounts vary from person to person. At this distance, a DNA test may find no shared DNA at all even when the relationship is certain. A half relationship (through only one shared ancestor instead of a couple) shares about half as much: 0.098%.
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 fourth cousin?
Your fourth cousin is the child of your parent’s third cousin: you share a set of 3rd great-grandparents. It works the same both ways: you are their fourth cousin too.
How much DNA do you share with a fourth cousin?
About 0.2% on average. Each generation of separation halves the expected amount, and individual results vary.
What is my fourth cousin’s child to me?
Your fourth cousin once removed.