Cousin Relationship Calculator

Determine the exact family relationship between you and your relatives based on your common ancestor

The common ancestor is my:

The common ancestor is my relative’s:

Your Relationship:

What Is a Cousin Relationship?

Cousin relationships describe how two people are related through a common ancestor. The degree of cousinship depends on how many generations separate each person from that shared ancestor. First cousins share grandparents, second cousins share great-grandparents, and so on. When cousins are from different generations, we add “removed” to describe the generational gap.

How Cousin Relationships Work

First Cousins

First cousins are the children of siblings. You share one set of grandparents with your first cousin, but you have different parents. This is the most common type of cousin relationship that most people are familiar with.

Second Cousins

Second cousins are the grandchildren of siblings. You share one set of great-grandparents with your second cousin. Your parents are first cousins to each other, making you second cousins.

Third Cousins and Beyond

The pattern continues with third cousins sharing great-great-grandparents, fourth cousins sharing great-great-great-grandparents, and so forth. The number of “greats” in your common ancestor’s title determines your cousin degree.

Removed Relationships

When cousins are from different generations, we describe them as “removed.” The number of times removed indicates the generational difference. For example, your parent’s first cousin is your first cousin once removed. Your grandparent’s first cousin is your first cousin twice removed.

Quick Reference Guide

Common Ancestor	Your Generation	Their Generation	Relationship
Grandparent	Grandchild	Grandchild	First Cousins
Grandparent	Grandchild	Great-Grandchild	First Cousins Once Removed
Great-Grandparent	Great-Grandchild	Great-Grandchild	Second Cousins
Great-Grandparent	Great-Grandchild	Great-Great-Grandchild	Second Cousins Once Removed
Great-Great-Grandparent	Great-Great-Grandchild	Great-Great-Grandchild	Third Cousins

How to Calculate Cousin Relationships Manually

You can work out cousin relationships by following these steps:

Identify the most recent common ancestor you share with your relative
Count how many generations separate you from that ancestor
Count how many generations separate your relative from that ancestor
The smaller number determines the cousin degree
Subtract the smaller number from the larger number to find how many times removed

Example: If your great-grandparent is your relative’s great-great-grandparent, you are 3 generations from the common ancestor whilst your relative is 4 generations away. The smaller number is 3, so you count the “greats” in great-grandparent (one “great”) and add 1, giving you second cousins. The difference is 4 – 3 = 1, so you are second cousins once removed.

Frequently Asked Questions

What does “removed” mean in cousin relationships?

“Removed” indicates a generational difference between cousins. If you and your cousin are not from the same generation relative to your common ancestor, you are “removed.” Once removed means one generation apart, twice removed means two generations apart, and so on.

Can you be a half-cousin?

Yes, half-cousins occur when you share only one grandparent instead of two. This happens when half-siblings have children. Half-cousins share half the DNA that full cousins would share.

What are double cousins?

Double cousins occur when two siblings from one family marry two siblings from another family. Their children are double first cousins because they share both sets of grandparents. Double cousins share twice as much DNA as regular first cousins.

How are first cousins once removed different from second cousins?

First cousins once removed are separated by one generation and share great-grandparents, whilst second cousins are from the same generation and also share great-grandparents. Your parent’s first cousin is your first cousin once removed, whilst your parent’s cousin’s child is your second cousin.

How much DNA do cousins share?

First cousins typically share about 12.5% of their DNA, second cousins share about 3.125%, and third cousins share about 0.78%. The percentage halves with each additional degree of cousinship. However, these are averages and actual amounts can vary.

Can this calculator help with genealogy research?

Absolutely. When building your family tree or researching ancestry, this calculator helps you accurately label relationships between family members. It’s particularly helpful when you discover distant relatives through DNA testing or historical records.

What’s the difference between patrilineal and matrilineal cousins?

These terms describe whether you’re related through the father’s side (patrilineal) or mother’s side (matrilineal) of the family. The cousin degree remains the same, but this distinction can be important for certain types of genealogical research or cultural traditions.

Tips for Family Tree Research

When researching your family history and mapping out cousin relationships, consider these helpful approaches:

Start with what you know and work backwards generation by generation
Document each relationship carefully, noting the common ancestor
Use DNA testing services to verify relationships and discover unknown cousins
Keep detailed records of birth, marriage, and death certificates
Interview older relatives to gather information about previous generations
Join genealogy websites and forums to connect with other researchers

Cultural Variations

Whilst this calculator follows the cousin naming conventions common in English-speaking countries, be aware that different cultures may use alternative systems. Some cultures have specific terms for maternal versus paternal cousins, or distinguish between older and younger cousins. When researching international family connections, it’s worth learning the local terminology.