Ex Post Facto

Business, Legal & Accounting Glossary

Definition: Ex Post Facto




What is the dictionary definition of Ex Post Facto?

Dictionary Definition


adj. Latin for “after the fact,” which refers to laws adopted after an act is committed making it illegal although it was legal when done, or increasing the penalty for a crime after it is committed. Such laws are specifically prohibited by the U.S. Constitution, Article I, Section 9. Therefore, if a state legislature or Congress enacts new rules of proof or longer sentences, those new rules or sentences do not apply to crimes committed before the new law was adopted.


Full Definition of Ex Post Facto


Ex post facto laws or laws “after the fact” are expressly forbidden by the United States Constitution in Article 1, Section 9, Clause 3. Under this clause, a person cannot be convicted and punished for a crime if the action was legal at the time it was performed but has since been made illegal.

For example, if someone was driving their car on Tuesday and the speed limit was 40 mph and the police clocked them under the speed limit but the next day the city changed the speed limit in the same area to 30 mph and because the officer had evidence the driver was driving over the speed limit the day before he decided to stop the lady and give her a ticket, under the concept of ex post facto she could not be charged with speeding because it was legal when she performed the action.

Some laws can be changed ex post facto which makes a formerly illegal act, legal. For example, some individuals dodged the draft for the Vietnam War but were given amnesty after the war and their once illegal act was no longer considered illegal.


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Ex Post Facto. PayrollHeaven.com. Payroll & Accounting Heaven Ltd. https://payrollheaven.com/define/ex-post-facto/ (accessed: September 22, 2021).
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Ex Post Facto. PayrollHeaven.com. Retrieved September 22, 2021, from PayrollHeaven.com website: https://payrollheaven.com/define/ex-post-facto/

Definition Sources


Definitions for Ex Post Facto are sourced/syndicated and enhanced from:

  • A Dictionary of Economics (Oxford Quick Reference)
  • Oxford Dictionary Of Accounting
  • Oxford Dictionary Of Business & Management

This glossary post was last updated: 28th April, 2020 | 2 Views.