retroactive

Retroactive, from Latin retro meaning backwards and actus meaning done, describes something that applies to or takes effect from a date in the past. In general use, a retroactive policy, law, or decision is effective retroactively, rather than from the date of its enactment.

In law, retroactivity refers to rules that apply to events or actions that occurred before the rule took effect. It can raise constitutional concerns, especially with criminal penalties, where prohibitions on ex post facto laws are common in many jurisdictions. Civil and administrative retroactivity is more widely accepted when the change is not punitive and serves legitimate regulatory or policy aims. The scope and limits of retroactive application are often determined by statutory text, case law, and constitutional principles.

Common contexts include tax measures that apply to the previous year, wage or benefit adjustments paid retroactively, and regulatory rule changes that affect past actions. Retroactive effects may be explicit, with a stated past effective date, or inferred through transitional provisions that bridge old and new regimes.

In other fields, retroactive can describe memory-related phenomena in psychology, such as retroactive interference, where new information affects the recall of previously learned material. It can also describe software, accounting, or policy updates that are applied to prior records or transactions. The precise interpretation depends on the legal, regulatory, or disciplinary context.