acalculator

What cousin are we?

Pick how many generations you and your relative are below the most recent ancestor you share. The cousin calculator names the relationship both ways.

Your numbers

They are your
2nd cousin once removed

They are your 2nd cousin once removed, and you are their 2nd cousin once removed.

You are their
2nd cousin once removed
Cousin degree
2
Times removed
1

They are your: 2nd cousin once removed. They are your 2nd cousin once removed, and you are their 2nd cousin once removed.

How to calculate

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.

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.

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.

  • 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”.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. You are the ancestor’s 2: grandchild, They are the ancestor’s 2: grandchild gives They are your 1st cousin, Cousin degree 1, Times removed 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. You are the ancestor’s 3: great-grandchild, They are the ancestor’s 4: great-great-grandchild gives They are your 2nd cousin once removed, You are their 2nd cousin once removed, Cousin degree 2, Times removed 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. You are the ancestor’s 3: great-grandchild, They are the ancestor’s 1: child gives They are your grandaunt or granduncle, You are their 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. You are the ancestor’s 2: grandchild, They are the ancestor’s 5: 3rd great-grandchild gives They are your 1st cousin 3 times removed, Cousin degree 1, Times removed 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. You are the ancestor’s 0: the common ancestor, They are the ancestor’s 6: 4th great-grandchild gives They are your 4th great-grandchild, You are their 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)

How it works

Let a be how many generations you are below your most recent common ancestor (1 = child, 2 = grandchild, 3 = great-grandchild), and b the same for your relative. Each can be 0 (that person is the ancestor) to 15.

What your relative is to you:

  • a = 0: they are your child (b = 1) or grandchild (b = 2), with greats for more generations.
  • b = 0: they are your parent (a = 1) or grandparent (a = 2), with greats for more generations.
  • a = 1 and b = 1: sibling.
  • a = 1, b ≥ 2: niece or nephew (b = 2), then grandniece or grandnephew (b = 3), with greats after that on both words (great-grandniece or great-grandnephew).
  • b = 1, a ≥ 2: aunt or uncle (a = 2), then grandaunt or granduncle (a = 3), with greats after that on both words (great-grandaunt or great-granduncle).
  • a ≥ 2 and b ≥ 2: cousins. Degree = min(a, b) − 1, written 1st, 2nd, 3rd, 4th, …; times removed = |a − b|, written "once removed", "twice removed", then "3 times removed" and so on, and left off at 0.
  • a = 0 and b = 0: no answer, since one person cannot be both.

Greats. The number of greats is the generations past the "grand" step: b − 2 for a grandchild, a − 2 for a grandparent, b − 3 for a grandniece, a − 3 for a grandaunt. One great is written "great-", two "great-great-", and three or more as an ordinal, "3rd great-", "4th great-", and so on.

You are their is the same rule with a and b swapped. The cousin degree and times removed show only for cousins. Words are gender-neutral: "aunt or uncle", "sibling".

Assumptions

  • The common ancestor is the most recent one you share (a couple counts as one ancestor).
  • Half relatives get the same names; add "half" in front.

Worked examples by hand

You and your relative share a grandparent (a = 2, b = 2). Degree 2 − 1 = 1st cousin, removed 0.

You are a great-grandchild of the ancestor (a = 3), they are a great-great-grandchild (b = 4). Degree min(3, 4) − 1 = 2, removed 4 − 3 = 1: 2nd cousin once removed, both ways.

Their parent is your great-grandparent (a = 3, b = 1). They are your grandaunt or granduncle; you are their grandniece or grandnephew.

a = 2, b = 5. Degree min(2, 5) − 1 = 1, removed 5 − 2 = 3: 1st cousin 3 times removed.

You are the ancestor (a = 0) and they are 6 generations down (b = 6). A grandchild with 6 − 2 = 4 greats: your 4th great-grandchild; you are their 4th great-grandparent.

Other questions people ask

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.