Unilateral Mistake

In one sentence

An error made by only one party to a contract about a material fact.

Plain English

A unilateral mistake occurs when just one person involved in a deal gets something wrong—like misunderstanding the price or the item being sold. Generally, courts won't cancel a contract just because one side made a mistake, especially if the other side didn't cause it or know about it. The mistaken party usually has to live with their error, unless the other side was dishonest or the mistake was so fundamental that enforcing the contract would be unconscionable (shockingly unfair).

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Example

You agree to buy a used car for $10,000, thinking it has 50,000 miles on it. After signing, you discover it actually has 150,000 miles. If the seller didn't mislead you and you had a chance to inspect it, your unilateral mistake about the mileage won't let you cancel the deal.

Used in a sentence

“The court ruled that the buyer's unilateral mistake about the property's square footage was not grounds for rescission.”

Related terms

Rescission

Unwinding a contract entirely, returning both parties to their positions before the deal.

Material Fact

A fact that significantly affects a party's rights, obligations, or decision-making in a contract.

Unconscionability

A contract term so unfair and one-sided that a court will refuse to enforce it.

Voidable Contract

A contract that one party can cancel or reject, but is otherwise valid.

Fraud

Intentional deception or misrepresentation made to trick someone into entering a contract or deal.

concealment

The act of hiding or keeping secret something that should be disclosed, especially in legal matters.

Offer

A proposal to enter into a binding agreement on specific terms.

Acceptance

Agreeing to the exact terms of an offer, creating a binding contract.

This page is a plain-English reference and is not legal advice. Laws vary by jurisdiction and change over time. For specific situations consult a licensed attorney.