What is a double first cousin?
Double first cousins happen when two siblings from one family marry two siblings from another — two brothers marrying two sisters, say. The children of those couples share all four grandparents instead of the usual two, so they are first cousins through both parents and genetically about twice as close, roughly on par with half-siblings.
Relationship
Double first cousin
- Two siblings from one family
- married two siblings from another
- their children are double first cousins
From the other side, you are their double first cousin.
Double first cousins descend from two shared grandparent couples at once, which a single-ancestor chart can't draw.
The calculator below works out blood relationships through a shared ancestor — use it to explore the rest of your tree.
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This relationship sits outside the shared-ancestor model, so the card above carries the answer and the calculator opens in its default state. Work out any blood relationship with it, or open the full relationship calculator.
FAQs
How much DNA do double first cousins share?+
About 25% on average — double the usual first-cousin figure and the same ballpark as half-siblings.
What is my double first cousin's child to me?+
Your double first cousin once removed — the 'removed' works exactly as it does for ordinary cousins.
Does the calculator store my family details?+
No — it runs entirely in your browser. Nothing you enter is uploaded or saved on our servers.
Start with one relative and see what comes back.
Add what you remember and AncestorIQ searches for the rest. Free to build your tree for as long as you like.
No credit card needed. Your tree stays yours.
