What is a second cousin?

Although most of us are confident in working out the cousins, aunts, uncles and even great-grandparents on our family tree, terms such as ‘second cousin once removed’ can be more of a challenge. It takes a bit of concentration and focus to grasp the concept, but when you see it on your family tree it becomes a little clearer.

So here’s how to calculate who’s who when exploring family relationships.

Quick links:

• What is a first cousin?
• What is a second cousin?
• What is a second cousin 'once removed'?
• Grab your copy of the Family Tree Relationship Calculator

What is a first cousin?

Let's start with the simple.

Your first cousin is the cousin with the closest relationship to you, with both of you sharing the same grandparent. Their parents will be your aunt and uncle, you probably know them well, spend Christmas with them, perhaps, or at least get to hear about what they're up to from your relatives.

What is a second cousin?

Moving logically on from this, a second cousin is one further step 'up the tree' and is a relative who shares the same great-grandparent with you. So they're more distant family members, and might be more familiar to your parents or grandparents.

You'll no doubt have worked out that the words ‘first’, ‘second’ or ‘third’, and so on, simply describe the number of generations between the cousin concerned and your common ancestor with them.

• First cousins share the same grandparents
• Second cousins have great-grandparents in common
• Third cousins share the same great-great-grandparents
• Fourth cousins share the same great-great-great-grandparents …and so on.

The family tree chart below helps to understand your relationship to a second cousin, and you'll obviously find many of these cousins when working on your genealogy. Some may even have researched much of your family tree, since you'll share many ancestors as you go back through the years. In fact, knowing your more distant cousins can be a great advantage when researching your genealogy, they might have vital information that was passed down on their side of the family. 

What is a second cousin 'once removed'?

Understanding the term 'removed' can add a layer of complexity, but it simply means that the first, second, etc cousins are in a different generation to each other.

The chart above shows this relationship, with 'YOU' on a different level than the 'FIRST COUSIN (once removed)'. The first cousin is in the same generation as your parents, aunts and uncles. In the chart above they are your parent's cousin.

'Removed' simply means 'one generation away' and it can go either up or down the family tree. So, for example, a second cousin once-removed is the child or parent of a second cousin. It can be a challenge to understand, so here's another chart to help out…

So our second chart shows that the 'second cousin once removed' (highlighted in green) is one generation away from 'YOU' - but it can be either way. We can see a 'second cousin once removed' both below and above the generation containing YOU and your cousins.

What about 'twice removed'?

The term 'twice removed' further adds to the generational gap, signifying a two-generation difference between relatives. Therefore, your second cousin's grandchild or your grandparent's second cousin would be referred to as 'twice removed'.

Generally speaking, and as you might imagine, first cousins possess a greater degree of shared genetic material compared to second cousins, while second cousins, in turn, exhibit a higher genetic resemblance than third cousins.

What about half cousins?

Just like you can have a half brother or sister, you can also have half cousins. This is when the two cousins have just one grandparent in common. Nobody needs telling that families can be complicated and so there are many different possible combinations - it might take a bit of working out, but it's worth it as we explore our family tree and discover new relatives, ancestors and, perhaps most excitingly, their many stories. 

Grab a copy of the Family Tree Relationship Calculator

For a quick and easy way to discover who’s who on your family tree, grab a copy of the relationship calculator.

Just sign up to receive the Family Tree newsletter and we'll send you a copy to download and print out.

To use the calculator, simply visualise the ancestor that you and another relative have in common and how they would describe you, eg you might both be a great-grandchild of that ancestor.

So on the horizontal column, find ‘great grandchild’ and with your finger, move along the chart, until the vertical column for ‘great grandchild’ meets that point – and you’ll see that the two of you are second cousins.

Or if you are that ancestor’s grandchild and your relative would be their great-grandchild, find the column on the horizontal row, then follow along looking at where the vertical column ‘great grandchild’ meets that point – the two of you are first cousins once removed, ie you are first cousins in different generations.

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