What is a father-in-law?
A father-in-law is the father of your spouse. The title arrives with the wedding: your spouse's parents become your father- and mother-in-law, and you become their son- or daughter-in-law in return. It is an affinal relationship — created by marriage — so you share family and often grandchildren, but no blood.
Relationship
Father-in-law
- You
- Your spouse
- Their father
From the other side, you are their child-in-law.
This connection runs through a marriage, not a shared ancestor, so the ancestor chart can't draw it.
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
Is my partner's father my father-in-law if we're not married?+
Formally the title comes with marriage, though plenty of long-term couples use it early.
Who am I to my father-in-law?+
His child-in-law — a son- or daughter-in-law.
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.
