What is a half-cousin?
Half-cousins share only one grandparent, because their parents are half-siblings. They are real blood relatives with about half the DNA full cousins share.
- Shared ancestor
- 2 generations up from you
- They call you
- their half-first cousin
- Average shared DNA
- ≈ 6.25%
- Cousin number · removed
- 1 · 0
Where "half" comes from
Full first cousins descend from a couple: both of their shared grandparents. If your parent and their parent had the same mother but different fathers (or vice versa), you share just one grandparent. That single shared ancestor makes you half first cousins.
The same logic applies further out: half second cousins share one great-grandparent instead of a couple.
Shared DNA
Half first cousins share about 6.25% of their DNA on average, around 450 centimorgans, which is roughly the same as a first cousin once removed. DNA sites therefore often list both possibilities for the same match.
Check your own relative
Not sure this is the right term? Enter your actual connection.
Find the most recent ancestor you both descend from, then say how each of you is connected to them.
- They call you
- their first cousin
- Expected shared DNA
- ≈ 12.5%
- Degree (civil / canon)
- 4 / 2
- Also called
- 1st cousin
Why a first cousin?
You share grandparents. You are 2 generations below them; the other person is 2 generations below them.
The cousin number comes from whoever is closer to the shared ancestor: 2 generations down, minus 1 = first cousin.
You are the same number of generations down, so there is no "removed".
Questions people ask
Are half-cousins real cousins?
Yes. They are blood relatives who share one grandparent.
Half-cousin or step-cousin?
Half-cousins share a grandparent by blood; step-cousins are connected only through a marriage.