What is a half cousin?
Half first cousins share one grandparent instead of two, because their parents are half-siblings.
Preset to this relationship. Change the steps to compare with neighbouring relationships.
They are your
half-first cousin
Common ancestor: your grandparent. Expected shared DNA: 6.25%
Shorter branch = 2 steps → 2 − 1 = 1 → first cousin. Branches differ by 0 → not removed.
Half first cousins share on average 6.25% of their DNA — half the 12.5% expected between full first cousins.
The same logic extends: half second cousins share one great-grandparent instead of a couple.
In everyday life most families simply say "cousin"; the half matters most when interpreting DNA matches.
To check a real pair of relatives, add them to the family tree maker and use How related?, or look them up on the cousin chart.
Questions
Are half cousins blood related?
Yes, through the one grandparent they share.
Is a half cousin the same as a step-cousin?
No. Step-cousins are joined by marriage only and share no ancestors.