Laws operate prospectively by default. A statute applies to events occurring after its enactment unless Congress clearly and explicitly states otherwise. Courts apply this presumption against retroactivity to protect settled expectations and avoid disrupting concluded transactions or finalized legal proceedings.
The First Step Act (2018) reduced penalties for certain drug offenses, but the Supreme Court held in Rutherford v. United States (2026) that defendants sentenced before enactment under the pre-2018 "stacking" provisions could not claim reduced sentences retroactively because Congress had not expressed clear retroactive intent. The Act's explicit retroactivity provision for crack cocaine sentences, by contrast, applied to past cases—illustrating that Congress must make retroactive application unmistakable.
Civil rights statutes and some remedial laws have been applied retroactively when courts find Congress intended to reach past conduct. The rule also has a constitutional dimension: the Ex Post Facto Clause bars criminal laws that increase punishment for conduct completed before enactment, but the presumption against retroactivity is broader and applies in civil contexts too.
Whether a new law applies to past cases determines whether people already sentenced actually benefit from criminal justice reform. When Congress reduces penalties without clear retroactivity language, people convicted under the old regime may serve sentences that no longer reflect current law.
Retroactivity doesn't mean a law was wrong when passed—it means whether a new law reaches back to change outcomes already determined. The Ex Post Facto Clause is related but narrower; it only bars retroactive laws that increase punishment. The general presumption against retroactivity is broader and applies to civil and remedial contexts as well.
Whether a new law applies to past cases determines whether people already sentenced actually benefit from criminal justice reform. When Congress reduces penalties without clear retroactivity language, people convicted under the old regime may serve sentences that no longer reflect current law.
Retroactivity doesn't mean a law was wrong when passed—it means whether a new law reaches back to change outcomes already determined. The Ex Post Facto Clause is related but narrower; it only bars retroactive laws that increase punishment. The general presumption against retroactivity is broader and applies to civil and remedial contexts as well.