Is your mother's cousin your second cousin or your first cousin once removed? If you are not sure, you are in good company. The system is actually simple once you know two rules.
Rule 1: Count the shared ancestor
The number in a cousin relationship tells you which ancestors you share:
- First cousins share grandparents.
- Second cousins share great-grandparents.
- Third cousins share great-great-grandparents.
Each step back adds one to the number.
Rule 2: "Removed" means different generations
When two cousins belong to different generations, we say they are "removed". The number of times removed is simply the number of generations between them.
- Your parent's first cousin is your first cousin once removed.
- Your first cousin's child is also your first cousin once removed.
- Your grandparent's first cousin is your first cousin twice removed.
A quick way to work it out
- Find the ancestor the two people share.
- Count how many generations each person is from that ancestor.
- If both counts are the same, they are cousins with no "removed". Two generations each is first cousins, three each is second cousins, and so on.
- If the counts differ, use the smaller count to find the cousin number, and the difference between the counts to find how many times removed.
Example: You are three generations from your great-grandparents. Your mother's cousin is two generations from the same couple. The smaller count is two, which means first cousins. The difference is one, so you are first cousins once removed.
Other useful terms
- Great-aunt or grand-aunt: your grandparent's sister.
- Half-siblings: siblings who share one parent rather than two.
- Step-relatives: relatives connected by marriage rather than by birth.
- In-laws: relatives of your spouse, or spouses of your relatives.
Why it matters
Clear relationship terms help you record your tree accurately, talk to newly found relatives with confidence and make sense of DNA match lists, which often estimate relationships in exactly these terms.