Third cousin once removed
A third cousin once removed is a relative of your own generation line, and the word works both ways: you are their third cousin once removed too.
The route
Red line: from you (4 steps up) and 5 steps down. Gold: the shared ancestor.
How to count it
Go up from you to the nearest ancestor you share with the other person. That takes 4 steps for you and 5 for them.
The smaller of the two, minus one, gives the degree: 3rd cousin. The two numbers differ by 1, so the cousins are once removed.
Cousin counting is the standard genealogical convention. Different families and legal systems sometimes use looser words, so check the naming conventions guide if a relative uses a different term.
Facts at a glance
| Term | third cousin once removed |
|---|---|
| Reciprocal | third cousin once removed |
| Steps up (a, b) | 4, 5 |
| Cousin degree | 3rd |
| Removal | 1 |
| Civil-law degree | 9 |
| Canon-law degree | 5 |
| Average DNA shared (full) | 0.39% |
| Average DNA shared (half) | 0.2% |
Full and half
The figures above assume full relatives, who share a couple as common ancestors. If the link runs through just one person, because of a remarriage or a different other parent, the relationship is a half relationship. It is usually written half third cousin once removed, and the average shared DNA falls to 0.2%. See full and half relatives.
The DNA numbers are theoretical averages. Real amounts vary a lot from one pair to the next, especially for distant cousins, so read the DNA guide before comparing against a test.
Check your own relationship in the calculator, or see where this term sits on the chart.