What are double first cousins?
Double first cousins share all four grandparents. It happens when a pair of siblings from one family marries a pair of siblings from another.
Preset to this relationship. Change the steps to compare with neighbouring relationships.
They are your
double first cousin
Common ancestors: your grandparents. Expected shared DNA: 25%
Shorter branch = 2 steps → 2 − 1 = 1 → first cousin. Branches differ by 0 → not removed.
Because they are related through both parents, double first cousins share about 25% of their DNA on average — similar to half-siblings or a grandparent and grandchild, and twice the figure for ordinary first cousins.
There is no special legal or medical concern with double cousins themselves; the higher DNA share mainly matters for reading DNA test results correctly.
In a family tree, draw both couples with their children; the cousin calculator on this site will show the ordinary first-cousin name, so add a note to flag the double link.
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
How common are double cousins?
Uncommon today but more frequent historically in small communities where two families intermarried.
Do double first cousins look like siblings?
They can, since they share as much DNA on average as half-siblings do.