Relationship calculator - how to work out family relationships

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’ or ‘natural child’ can be more of a challenge. So here’s how to calculate who’s who when exploring family relationships.

Cousin relationships

We’ll begin with cousins, who are of course, the children of an individual’s uncle or aunt. The words ‘first’, ‘second’ or ‘third’ and so on, simply describe the number of generations between the people concerned and their common ancestor.

So –

• first cousins share the same grandparents
• second cousins have great-grandparents in common
• third cousins share the same great-great-grandparents.

The words ‘once removed’ when describing family members means that the first, second, etc cousins are in a different generation to each other. So, for example, a second cousin once-removed is the child or parent of a second cousin.

Base and natural child

During your family tree research, you will probably come across one or more terms used to describe an illegitimate child. Such terms can include -

• Base born
• Natural
• Bastard

Each of the above can mean a child born out of wedlock, ie an illegitimate child. Although such terms can vary from document to document, as a rule of thumb, a ‘base’ child is usually the child of a single mother, whereas ‘bastard’ generally means the child of an unmarried but established couple’ and ‘natural child’ refers to a blood child rather than one who is adopted, or a step-child.

For a quick and easy way to discover who’s who on your family tree, check out our handy relationship calculator. To use the calculator, simply visualise how the ancestor that you and another relative have in common 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.