Ex post facto law

Ex post facto law constitutional

A law that punishes something you did before the law existed, or increases the punishment after the fact. The Constitution forbids these.

Technical: A retroactive penal law forbidden by Art. I, §§9–10; Calder v. Bull, 3 U.S. (3 Dall.) 386 (1798), confined the prohibition to criminal (not civil) laws that, e.g., criminalize past conduct or increase punishment retroactively.

Founding-era note: Calder v. Bull (1798) is the founding-era case that settled the term's scope as criminal-only in U.S. constitutional law.

Sources: Calder v. Bull, 3 U.S. 386 (1798)

A dictionary entry is reference: it describes how a term is used. It is not itself binding law. Why that matters →

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