Half Cousin
See what a half cousin is, drawn as a family diagram with only one shared ancestor at the top. Change the degree and the removal for any other half cousin.
Free · runs in your browser · nothing is uploaded
Recent
Your last 10 settings, saved only in this browser. Nothing is uploaded.
How to find out who is your half 1st cousin
- Read the heading “Your half 1st cousin” and the sentence under it. It names who the relative is in words.
- Press a chip such as “1st cousin once removed” to jump to another relationship.
- Or set “Cousin degree” (1st to 10th) and “Times removed” (0 to 10) yourself.
- Under “Who is younger?” choose whether they are younger than you or older than you. With 0 times removed, both of you are in the same generation.
- Press “Swap viewpoint” to see the relationship from their side. The tiles “Seen from you” and “Seen from them” give the wording for each of you.
- Under “Shared ancestors” choose “One person (half cousins)” if you share only one ancestor.
- Look at the family diagram. It shows the common ancestors at the top, your line on the left and their line on the right.
- Read “Generations from the common ancestor” and “Expected shared DNA” for the numbers behind the name.
- Read the line under the diagram. It says how many generations you and they are below the shared ancestor and which person in the diagram is the cousin.
- Press a neighbouring chip, for example the next degree or one more removal, and watch the two generation numbers and the DNA figure change.
- Press “Copy link to this result” to share the exact relationship.
What is a half cousin?
A half cousin is a cousin with whom you share only one common ancestor. Full cousins share both grandparents, the couple. For half 1st cousins, one grandparent had children with two different partners, and your parent and theirs are half-siblings. The word half describes the shared ancestors, not how close the two people are as cousins.
Are half cousins blood related?
Yes. Half cousins descend from the same grandparent, so they are related by blood through that one person. They are not related through the other grandparents.
What is the difference between a half cousin and a full cousin?
A full 1st cousin shares a couple of grandparents, and the diagram shows two ancestors at the top. A half 1st cousin shares one, and the diagram shows one. The cousin degree is the same, since it depends only on how many generations separate you from the shared ancestor. The expected shared DNA is halved.
| Relationship | Generations (you and them) | Full relatives | Half relatives |
|---|---|---|---|
| 1st cousin | 2 and 2 | 12.5% (1/8) | 6.25% (1/16) |
| 1st cousin once removed | 2 and 3 | 6.25% (1/16) | 3.125% (1/32) |
| 2nd cousin | 3 and 3 | 3.125% (1/32) | 1.5625% (1/64) |
| 3rd cousin | 4 and 4 | 0.78125% (1/128) | 0.39063% (1/256) |
How much DNA do half cousins share?
For half 1st cousins the average is 6.25%, which is 1/16 of the genome, against 12.5% for full 1st cousins. These are theoretical averages over many pairs and real amounts vary, so DNA cannot prove or disprove a half relationship on its own. A half 1st cousin and a full 1st cousin once removed average the same figure.
Is a half cousin the same as a second cousin?
No. Full second cousins share great-grandparents and average 3.125% of DNA. Half 1st cousins share one grandparent and average 6.25%. The names answer different questions: how far back the shared ancestor is, and how many of them there are.
What is a half cousin once removed?
The child of your half cousin, or the half cousin of your parent. The generation counts are 2 and 3 and the expected DNA is 3.125% (1/32).
What are the four types of cousins?
There is no official list of four. The groups usually meant are 1st, 2nd and 3rd cousins by degree, plus half cousins. “Removed” is a separate idea: it counts generations between two people and can be added to any of them.
Frequently asked questions
Are half cousins real cousins?
Yes. They are cousins who share one ancestor instead of two, and the cousin degree is counted in the same way as for full cousins.
How do half cousins appear in a DNA test?
A half 1st cousin is expected to share about 6.25% of DNA, the same average as a full 1st cousin once removed. Several relationships overlap, so a DNA match alone cannot name the relationship.
Can half cousins be the same age as me?
Yes. Cousins are in your generation, but generation is not age. A half cousin can be older or younger than you.
What is a half cousin chart?
A cousin chart whose cells are halved. The cousin chart has a setting “Shared ancestors” with “One person (half cousins)” that fills the table with the half names and half the DNA.
Are double first cousins half cousins?
No, the opposite. Double first cousins are cousins through two pairs of siblings, so they share both sets of grandparents. Their expected DNA is about 25%, twice the figure of ordinary first cousins. This page shows cousins through a single line only.
Does this upload my information?
No. Only the numbers you choose are used, and they stay in your browser.
- Third Cousin: shared ancestors, the chart and the DNA of third cousins.
- Second Cousin Once Removed: the child of your second cousin or the second cousin of your parent.
- First Cousin Once Removed: the most searched relationship, explained from both sides.
- Cousin Calculator: work from the common ancestor to the name.
- Cousin Chart: all cousin degrees and removals in one table.
- Relationship Calculator: relationships between two people in a tree.
- Relationship Chart: the chart of family relationships.
- Inbreeding Coefficient Calculator: how related two parents are.
- Kinship Terms: relationship words in other languages.
- How Many Ancestors Calculator: ancestors per generation.
- Gedcom Viewer: open a family tree file.