Family relationships
Family relationships explained
"Second cousin once removed" sounds like it needs a diagram, and it does — but only a small one. Removed means a generation apart, not a distance apart. Once you know that one thing, the whole system falls into place, and these guides walk through the rest.
The two rules that explain everything
Almost every cousin question comes down to two ideas. Learn these and you can work out any relationship on paper.
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The cousin number comes from the shared ancestor. First cousins share grandparents. Second cousins share great-grandparents. Third cousins share great-great-grandparents. Each step further back adds one to the number.
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"Removed" counts generations between you. Same generation, no removal. One generation apart, once removed. Two apart, twice removed. It has nothing to do with how close you are or how well you know them.
Working it out from the shared ancestor
Find the most recent ancestor you both share, then count generations down to each of you. This table does the rest.
| Your shared ancestor is… | …their grandchild | …their great-grandchild | …their great-great-grandchild |
|---|---|---|---|
| Your grandparent | First cousins | First cousins once removed | First cousins twice removed |
| Your great-grandparent | First cousins once removed | Second cousins | Second cousins once removed |
| Your great-great-grandparent | First cousins twice removed | Second cousins once removed | Third cousins |
The mistake almost everyone makes. A second cousin is not the same as a first cousin once removed. Your second cousin is in your own generation and shares your great-grandparents. Your first cousin once removed is usually your first cousin's child — one generation down, and a noticeably closer blood relationship.
Guides in this section
We're building these out one at a time. Each explains the relationship in plain English and shows how to record it correctly in your tree.
Section in progress. The individual relationship guides and the interactive relationship calculator are still being written. This page carries the core explanation in the meantime, so nothing here is a dead end. Links will be added as each guide is published.
Recording relationships in your tree
Knowing what to call someone is half the job. Getting the software to agree is the other half, and it's where most trees go wrong.
- Half and step relationships need recording differently. A half sibling shares one biological parent; a step sibling shares none. Only one is a blood relationship, and entering a step-parent as a biological one quietly corrupts every calculation downstream.
- Adoptive parents belong in the tree, recorded as adoptive rather than biological, so both the legal family and the biological line stay accurate.
- The same person entered twice — which happens constantly after an import or sync — breaks relationship calculations entirely, because the software sees two different people. See merging duplicate people.
- Pedigree collapse is normal in older trees. When distant cousins married, an ancestor appears in more than one line. That's genuine history, not an error to be tidied away.
Relationships showing wrong in your tree?
Usually duplicates, or a step-parent recorded as biological. We'll find it and put the structure right.
Frequently asked questions
What does removed mean in a cousin relationship?
It refers to a difference in generation, not to distance or estrangement. Cousins in the same generation have no removal. Each generation of difference adds one — so your first cousin's child is your first cousin once removed.
How do I work out what cousin someone is?
Find the most recent ancestor you share. Count generations from that ancestor down to each of you. The smaller count minus one gives the cousin number; the difference between the two counts gives the removals. The table above does it for you.
Is a second cousin the same as a first cousin once removed?
No — this is the most common mix-up in genealogy. A second cousin shares your great-grandparents and is in your generation. A first cousin once removed is one generation away, typically your first cousin's child or parent, and a closer blood relative.
What is the difference between a half sibling and a step sibling?
A half sibling shares one biological parent with you. A step sibling shares none and is connected through a marriage between your parent and theirs. Only one is a blood relationship, which is why they must be recorded differently in your tree.