Free cousin calculator

Free Cousin Relationship Calculator

A cousin relationship calculator identifies how two relatives connect by comparing how many generations each person is from the same ancestor. If both branches end at the same depth they stay in the same cousin line, and if one branch goes farther the relationship is removed by that generation gap.

Use this free cousin relationship calculator to answer questions like "what is my cousin's child to me" or "what does cousin once removed mean" with a formula-based explanation and visual branch diagram.

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Formula and relationship diagram

The calculator uses the standard cousin formula: cousin degree equals the smaller depth minus one, and removal equals the absolute difference between the two depths.

min(N, M) - 1|N - M|Live diagram

Cousin degree

1

min(2, 3) - 1

Removal

1

|2 - 3|

Final label

First cousin once removed

Cousin

Formula takeaway

The smaller depth sets the cousin line, and the gap between the two depths becomes the removal count.

Shared ancestor diagram

Both branches start from the same ancestor and step down to Person A and Person B.

Common ancestor
Shared ancestor

Person A branch

Grandchild

2 gen down

Generation 1

Child

Generation 2

Grandchild

Person A

Person B branch

Great-grandchild

3 gen down

Generation 1

Child

Generation 2

Grandchild

Generation 3

Great-grandchild

Person B

How to use the cousin relationship calculator

Step 1

Choose Person A's generation

Select how far Person A sits below the shared ancestor, starting with child, grandchild, or deeper generations.

Step 2

Choose Person B's generation

Select Person B's distance from that same common ancestor using the same generation list.

Step 3

Read the cousin line and removal

The calculator applies the cousin formula, shows the exact relationship, and tells you whether the pair is first cousins, second cousins, or removed.

Step 4

Use the visual explanation

Check the branch diagram and formula summary to see why the relationship is correct and how the generation gap affects the result.

Cousin calculator FAQ

Straight answers for the cousin questions that come up most often in family history research.

What is a cousin once removed?

A cousin once removed is a cousin relationship with a one-generation gap. Your parent's first cousin is your first cousin once removed, and your first cousin's child is also your first cousin once removed.

What is my cousin's child to me?

Your first cousin's child is your first cousin once removed. The cousin line stays the same, and the word removed tells you there is one generation of difference between the two people.

How do you calculate cousin relationships?

Count how many generations each person is from the shared ancestor. If both are at least grandchildren of that ancestor, the cousin degree is the smaller number minus one, and the removal is the difference between the two generation counts.

Are second cousins related by blood?

Yes. Second cousins share the same great-grandparents. They are in the same cousin line because both people are three generations away from the shared ancestor.

Can a cousin calculator show siblings or aunts and uncles too?

Yes. When one or both people are only one generation below the shared ancestor, the relationship is no longer a cousin line. The calculator can identify siblings, aunt and uncle relationships, and niece or nephew relationships in those edge cases.