What is a second cousin?
Your second cousin is the grandchild of your grandparent's sibling. You share a set of great-grandparents, and both of you are three generations below them.
Preset to this relationship. Change the steps to compare with neighbouring relationships.
They are your
second cousin
Common ancestors: your great-grandparents. Expected shared DNA: 3.13%
Shorter branch = 3 steps → 3 − 1 = 2 → second cousin. Branches differ by 0 → not removed.
Put another way: your parent and your second cousin's parent are first cousins to each other. When first cousins have children, those children are second cousins.
Second cousins share on average about 3.125% of their autosomal DNA (1/32). Because DNA is inherited in random chunks, the real figure varies widely — roughly 1.5% to 5% is typical in testing-company data such as the Shared cM Project.
People often call a parent's first cousin a "second cousin". That relative is actually your first cousin once removed — a different generation from you.
To check a real pair of relatives, add them to the family tree maker and use How related?, or look them up on the cousin chart.
Questions
Is a second cousin blood related?
Yes. You share a set of great-grandparents, so you are blood relatives, typically sharing around 3% of your DNA.
What is my second cousin's child to me?
Your second cousin once removed.
Is my mom's cousin my second cousin?
No. Your mother's first cousin is your first cousin once removed. Their children are your second cousins.