What is a third cousin once removed?
Your third cousin once removed is either your third cousin's child or your parent's third cousin. One of you is four generations below the shared ancestors, the other five.
Preset to this relationship. Change the steps to compare with neighbouring relationships.
They are your
third cousin once removed
Common ancestors: your great-great-grandparents. Expected shared DNA: 0.391%
Shorter branch = 4 steps → 4 − 1 = 3 → third cousin. Branches differ by 1 → once removed.
Expected shared DNA is about 0.39% (1/256) on average. At this distance a sizeable share of real third cousins once removed share no detectable DNA in consumer tests, so a missing DNA match does not disprove a paper relationship.
Your children and your third cousin's children are fourth cousins to each other.
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
What is my parent's third cousin to me?
Your third cousin once removed.
What is my third cousin's child to me?
Your third cousin once removed.