If you’ve spent any time researching your family tree — or exploring your DNA matches on sites like Ancestry — you’ve probably come across terms like second cousin or second cousin once removed.
These phrases can be confusing at first, but understanding them is key to making sense of your family connections and using them to further your genealogy research. Let’s break it down clearly, with plenty of examples to make the concept stick.
What Is a Second Cousin: The Basics
To understand what a second cousin is, it helps to start with the basics:
First cousins share the same grandparents.
Second cousins share the same great-grandparents.
So, if you and another person both descend from a pair of shared great-grandparents, but not the same grandparents, you’re second cousins.
Let’s look at a hypothetical example:
Your great-grandparents, John and Ophelia Williams, had two children: Anna and James.
- Anna’s child is Caroline (your mother).
- James’s child is Robert.
- Caroline’s child is you, and Robert’s child, David, is your second cousin.
You and your second cousin David are both great-grandchildren of John and Ophelia, but you have different grandparents and parents.
You can think of it like this:
- Siblings share parents.
- First cousins share grandparents.
- Second cousins share great-grandparents.
Each time you move to the next “degree” (first, second, third), you move one generation further back to find your shared ancestor.
What Is a Second Cousin Once Removed?
The word removed simply describes a difference in generations. “Once removed” means there’s a one-generation difference between you and that cousin.
Let’s return to the previous example:
You and David are second cousins. David has a daughter named Emma. Emma is your second cousin once removed. Why? Because Emma is one generation below you.
The same works in reverse. Your mother’s second cousin Robert is your second cousin once removed. In this case, he is one generation above you (the same generation as your mom). The relationship goes both ways—what changes is the generational level.
What Is a Second Cousin Twice Removed?
Now that you understand “once removed,” you can probably guess that “twice removed” means there’s a two-generation difference.
Let’s suppose that your second cousin once removed, Emma, just had a child named Noah. You guessed it: Noah is your second cousin twice removed — two generations below you.
Conversely, you would be Noah’s second cousin twice removed in the opposite direction — two generations above him.
It’s a flexible term that simply accounts for generational distance.
Still Confused? Here’s a good rule of thumb: Count back to the shared ancestor. Count down each person’s line to the individual. The smaller number of generations determines the “cousin” level, and the difference in generations is the “removed.”
What’s Age Got to Do with It?
I’ve sometimes heard people say that “removed” refers to people older or younger than you. But this isn’t always true. For example, let’s look at two of my second cousins twice removed.
Joan is my grandmother’s second cousin (same generation as her), therefore twice removed from me. However, she is decades younger than my grandmother and also much younger than my mother. It’s her generation that makes her twice removed, not her age.
Jason is also my second cousin twice removed. He is only a few years younger than me, however, I’m the same “generation” as his grandmother Elizabeth.
Keep this in mind when analyzing relationships. People could have children at varying ages that affects the generations.
Why Second Cousins Matter in Genealogy
Now that you understand the terminology, let’s talk about why this matters.
In genealogy — and especially in DNA research — your second (and third cousins and beyond) are often some of your most valuable matches. Here’s why:
They share enough DNA to be useful, but not so much that it’s confusing.
A second cousin shares about 3.125% of your DNA (roughly 200 centimorgans).
These levels are strong enough to indicate a real genealogical connection but distant enough to help identify specific ancestral lines. In other words, they help you identify your great-grandparents and beyond.
If you match a group of second cousins on Ancestry, for example, you can use this connection to identify which great-grandparents you all share. Once you pinpoint that shared ancestral couple, it becomes much easier to trace their parents — your great-great-grandparents — and extend your tree further. Cousin clusters lead to ancestor breakthroughs.
By grouping your DNA matches by shared segments or using Ancestry’s “Shared Matches” feature, you can identify which side of the family your cousins belong to—maternal or paternal—and sometimes pinpoint exactly which ancestral couple connects you all.
Second Cousins: Bringing It All Together
Understanding how second cousins (and their “removed” variations) fit into your family tree can unlock powerful insights in your genealogy research.
When you spot a DNA match labeled “second cousin once removed,” don’t just shrug and move on—use that information to map out where your family lines connect. Look for shared surnames, ancestral locations, and other mutual DNA matches.
Every cousin connection represents a piece of your ancestral puzzle. The more clearly you understand those relationships, the faster and more accurately you can identify the ancestors you share.
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