What is a half cousin?
Short answerHalf cousins are cousins whose parents are half-siblings, so they share one grandparent instead of a grandparent couple. Half first cousins share about 6.25% of their DNA on average, half the amount full first cousins share. In everyday speech most families simply call them cousins.
Where half cousins come from
If your father and your aunt share a mother but have different fathers, they are half-siblings. Their children, you and your cousin, share only that grandmother: you are half first cousins.
How Family Trees names them
The app uses “half” only for siblings and calls the next generation first cousins, which matches everyday use. Their shared grandparent is visible on the tree, so the half relationship is clear when you look.
Half cousins and DNA
Shared DNA halves at every half link. Half first cousins average around 6.25%, close to full first cousins once removed, which is why DNA matches alone can’t always tell those two apart.
Let Family Trees name it for you
Every parent link in Family Trees is birth, adoptive, step or foster, and every couple is married, partners, separated or divorced. From that, the app names each relative in plain words on their page and under How are they related?, including half, step, foster and in-law relations. It’s free for up to 100 people.
Questions
Are half cousins blood related?
Yes, through the one grandparent they share.
How much DNA do half first cousins share?
About 6.25% on average, half of what full first cousins share.