What Is a Second Cousin? Calculate Your Cousin Relationships

When it comes to cousins, the relationship possibilities are endless. Your number of grandparents doubles with each generation. Count back 10 generations, and that’s 2,046 total ancestors, which means the potential cousin population is exponential. You could have millions of them: fourth cousins, second cousins three times removed, tenth cousins twice removed—we could go on. 

With DNA testing, Facebook, online family trees, and message boards that can connect you to new cousins every day, you’re bound to become curious about precisely how you’re related. 

Here’s how you determine the kind of cousins you are based on degrees of separation from shared ancestors.

What Makes Someone a Cousin?

The fact that you share an ancestor with that person. To understand cousin relationships, remember that your ancestors are only the people in your direct line: parents, grandparents, great-grandparents, and so on. Your ancestors’ siblings are aunts and uncles (no matter how many “greats” you count)—not ancestors.

Just about any other blood relative who is not your sibling, ancestor, aunt, or uncle is your cousin. To determine your degree of cousinhood—first, second, third, etc.—you need to identify the ancestor you share with your cousin and how many generations separate each of you from that ancestor.

What is a First Cousin?

Your first cousin (aka full cousin) is the child of your aunt or uncle. The most recent ancestor you and your first cousin share is your grandparent. You typically share 12.5 percent of your first cousin’s DNA.

What is a Second Cousin?

Your second cousins are the children of your parents’ first cousins. You and your second cousins have the same great-grandparents! You typically share 3.125 percent of your second cousin’s DNA. 

What is a Third Cousin?

Third cousins’ most recent common ancestors are great-great-grandparents. There’s a 90% chance third cousins share DNA. That said, third cousins who share DNA only typically share .781% of their DNA with each other.

What Is a “Removed” Cousin?

A “remove” happens when two cousins have different numbers of generations back to their most recent common ancestor. One generation of difference equals one remove.

To calculate this, count the number of generations from each cousin back to the common ancestor. The cousin with the lower number of generations determines the degree of cousinhood—first, second, third, and so on. Subtract the lower number of generations from the higher number to find out how many times removed the cousins are.

Double Cousins

This is a special cousin category for the offspring of brothers- and sisters-in-law. For example: Your sister weds your husband’s brother. Instead of sharing one set of grandparents, as first cousins do, double cousins share both sets of grandparents. As you might expect, double cousins have more DNA in common than typical first cousins—about 25 percent.

Kissing Cousins

A kissing cousin is not a cousin you marry. Instead, it’s any distant relative whom you know well enough to give a “hello” kiss to at family gatherings. 

This begs the question: How close a cousin is too close to wed? States have different laws governing consanguineous marriages. It’s best to ask a lawyer about statutes for the state in question.

Who’s Not a Cousin?

Due to limited mobility in our ancestors’ day, most of us have instances in our family trees of cousins who married, knowingly or unknowingly. This means that you can be related to the same person in multiple ways.

Someone you’re related to by marriage, rather than by blood, is not your cousin. You might be in-laws, or your relationship might be “good friends.”

You can learn more about collateral degree calculation (aka family relationships) in Lois Horowitz’s Dozens of Cousins (Ten Speed Press, 2004) or Jackie Smith Arnold’s Kinship: It’s All Relative (Genealogical Publishing Co., 2009).

Speaking of family, let’s talk about family names! See our article about baby names trends and the baby-naming game!