# What cousin are we?

Names how two relatives are related, such as second cousin once removed or grandaunt, from how many generations each is below the ancestor they share.

- Page: https://www.acalculator.org/everyday-life/cousin-calculator
- JSON spec: https://www.acalculator.org/everyday-life/cousin-calculator.json
- Version: 9a701249cef2

## Default answer

Example with the default inputs (You are the ancestor’s 3: great-grandchild, They are the ancestor’s 4: great-great-grandchild): They are your 2nd cousin once removed, and you are their 2nd cousin once removed.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| a | You are the ancestor’s | How many generations you are below the most recent ancestor you both share. |
| b | They are the ancestor’s | How many generations your relative is below that same ancestor. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| relationship | They are your | What your relative is to you. |
| reverse | You are their | What you are to your relative. |
| degree | Cousin degree | Fewer generations − 1, for cousins: 1 for first cousins, 2 for second. |
| removedBy | Times removed | The generation gap between you, for cousins. |

## Method

With a and b the generations each person is below the most recent common ancestor: cousins (a, b ≥ 2) are (min(a, b) − 1)th cousins, |a − b| times removed; a = 1 or b = 1 gives siblings, aunts, uncles, nieces and nephews; a = 0 or b = 0 a direct line.

## Assumptions

- The common ancestor is the most recent one the two people share.
- Names are the same for half relatives (who share one ancestor of a couple instead of both); genealogists then add “half”.

## Worked examples

1. a = 2, b = 2 gives relationship = 1st cousin, degree = 1, removedBy = 0. Source: FamilySearch, What Is a Second Cousin? Cousin Relationships Explained (first cousins share a grandparent, second cousins a great-grandparent; removed is the generation gap), https://www.familysearch.org/en/blog/what-is-a-second-cousin (retrieved 2026-10-18).
2. a = 3, b = 4 gives relationship = 2nd cousin once removed, reverse = 2nd cousin once removed, degree = 2, removedBy = 1. Source: FamilySearch, What Is a Second Cousin? Cousin Relationships Explained (first cousins share a grandparent, second cousins a great-grandparent; removed is the generation gap), https://www.familysearch.org/en/blog/what-is-a-second-cousin (retrieved 2026-10-18).
3. a = 3, b = 1 gives relationship = grandaunt or granduncle, reverse = grandniece or grandnephew. Source: Family Tree Magazine, How to Refer to Aunts and Uncles: Grand, Not Great (aunt, grandaunt, great-grandaunt; a sibling’s grandchild is a grandniece or grandnephew), https://familytreemagazine.com/general-genealogy/aunts-and-uncles-grand-not-great/ (retrieved 2026-10-18).
4. a = 2, b = 5 gives relationship = 1st cousin 3 times removed, degree = 1, removedBy = 3. Source: FamilySearch, What Is a Second Cousin? Cousin Relationships Explained (first cousins share a grandparent, second cousins a great-grandparent; removed is the generation gap), https://www.familysearch.org/en/blog/what-is-a-second-cousin (retrieved 2026-10-18).
5. a = 0, b = 6 gives relationship = 4th great-grandchild, reverse = 4th great-grandparent. Source: Family Tree Magazine, How to Refer to Aunts and Uncles: Grand, Not Great (aunt, grandaunt, great-grandaunt; a sibling’s grandchild is a grandniece or grandnephew), https://familytreemagazine.com/general-genealogy/aunts-and-uncles-grand-not-great/ (retrieved 2026-10-18).

## FAQ

### How do I work out what cousin someone is?

Find the most recent ancestor you share and count the generations from that ancestor down to each of you. Take the smaller count and subtract 1: that is the cousin degree. The difference between the two counts is how many times removed. If you are both great-grandchildren of the ancestor (3 generations), you are 3 − 1 = 2nd cousins.

### What does once removed mean?

It means you are one generation apart. Your parent’s first cousin is your first cousin once removed, and so is your first cousin’s child. Twice removed is two generations apart.

### What is the difference between a second cousin and a first cousin once removed?

Second cousins are in the same generation and share great-grandparents. A first cousin once removed is a generation above or below you: your first cousin’s child, or your parent’s first cousin.

### Is my grandparent’s sister my great-aunt or my grandaunt?

Both are used. Genealogists prefer grandaunt, because “grand” marks two generations, just like grandparent. Her parents are your great-grandparents, so she is to them what your grandparent is. This page uses grandaunt and granduncle.

### What are my cousin’s children to my children?

Second cousins. Your children and your first cousin’s children are both great-grandchildren of the same couple, so each is 3 generations below them, and 3 − 1 = 2.

### What is a half cousin?

Half cousins share only one ancestor of the couple, because their parents were half siblings. The degree and removal count the same way; add “half” in front, such as half first cousin.

## Sources

- FamilySearch, What Is a Second Cousin?—Cousin Relationships Explained (cousins share an ancestor at least 2 generations back; first cousins share a grandparent, second cousins a great-grandparent; “removed” is the generation gap). https://www.familysearch.org/en/blog/what-is-a-second-cousin (retrieved 2026-10-18)
- Family Tree Magazine, Genealogy Q&A: How to Refer to Aunts and Uncles: Grand, Not Great (parent, aunt or uncle; grandparent, grandaunt or granduncle; great-grandparent, great-grandaunt; a sibling’s grandchild is a grandniece or grandnephew). https://familytreemagazine.com/general-genealogy/aunts-and-uncles-grand-not-great/ (retrieved 2026-10-18)