Would a law retroactively increasing the penalties for a crime, but not criminalizing any formerly legal action, be constitutional, or would it be considered ex post facto?

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    Related: law.stackexchange.com/questions/90600/… I hesitated to suggest it might be a duplicate, but I feel like both questions are different enough, legally speaking.
    – Clockwork
    Commented Oct 17, 2023 at 7:39
  • Inn which jurisdiction, please? Here in the UK it's a principle so basic, it might be an axiom: retroactive law is not allowed, including details like increased penalties. Commented Oct 20, 2023 at 18:35
  • @RobbieGoodwin mainly the United States, but answers from other jurisdictions are welcome as well.
    – Someone
    Commented Oct 20, 2023 at 20:03
  • Thanks, Someone, and which of the States are you looking at - or is this Federal law, or a rare instance in which all States agree, or what? How could '(not) criminalizing (anything)' come into this, except to show neither guilt nor penalty being subject to retroactive change? Commented Oct 22, 2023 at 0:20
  • @RobbieGoodwin I'm asking about the US federal Constitution, but I think the federal constitutional prohibition on ex post facto laws applies to states too? The part about not criminalizing anything is relevant because a law that retroactively criminalizes conduct that was legal at the time is certainly ex post facto.
    – Someone
    Commented Oct 22, 2023 at 0:40

3 Answers 3


Such a law would be prohibited under the ex post facto clause of the Constitution.

A (very!) early Supreme Court case on this was Calder v. Bull (1798), in which Samuel Chase wrote

I will state what laws I consider ex post facto laws within the words and the intent of the prohibition. 1st. Every law that makes an action done before the passing of the law and which was innocent when done, criminal and punishes such action. 2d. Every law that aggravates a crime, or makes it greater than it was when committed. 3rd. Every law that changes the punishment, and inflicts a greater punishment than the law annexed to the crime, when committed. 4th. Every law that alters the legal rules of evidence and receives less or different testimony than the law required at the time of the commission of the offense in order to convict the offender.

(As it happens, Calder v. Bull was actually about a civil case under Connecticut state law, and the Court found that the ex post facto clause did not apply to it.)

By the time of Beazell v. Ohio (1925), the court didn't even feel like they needed to provide citations for this question any more:

It is settled, by decisions of this Court so well known that their citation may be dispensed with, that any statute which punishes as a crime an act previously committed, which was innocent when done, which makes more burdensome the punishment for a crime, after its commission, or which deprives one charged with crime of any defense available according to law at the time when the act was committed, is prohibited as ex post facto.

Note, however, that the scope of this protection is effectively limited to the categories listed in Calder. There were a couple of late 19th-century Supreme Court decisions (Kring v. Missouri (1883); Thompson v. Utah (1898)) in which changes to criminal court procedures that disadvantaged defendants were successfully challenged under the ex post facto clause. However, in Collins v. Youngblood (1990), the court explicitly overruled these precedents and basically said "ex post facto only applies to the four categories in Calder."

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    lowering the punishment however is permitted
    – Trish
    Commented Oct 16, 2023 at 22:04
  • @Trish yes, and then there's the gray area of changing one punishment for another that's considered not greater nor lower. The Judicial System sometimes feels like a self-feeding machine, perpetual motion. Commented Oct 17, 2023 at 15:18
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    The legislature can make the lesser punishment apply retroactively, but there's no federal constitutional right to lex mitior in the US as there is in some countries. If the law doesn't provide for retroactive application, then the defendant gets sentenced according to the law that was in effect at the time they committed the crime.
    – Brian
    Commented Oct 18, 2023 at 18:12
  • Note that "ex post facto" applies only to "punishments", so civil restrictions based upon a current threat to the public posed by previously convicted sex offenders imposed after their convictions aren't automatically invalid as ex post facto punishments.
    – ohwilleke
    Commented Oct 18, 2023 at 19:53

In Canada, this is answered by section 11(i) of the Canadian Charter of Rights and Freedoms:

Any person charged with an offence has the right ... if found guilty of the offence and if the punishment for the offence has been varied between the time of commission and the time of sentencing, to the benefit of the lesser punishment.

The offender has the right to the benefit of the lesser punishment.


Such a law would not be consistent with the European Convention on Human Rights, article 7, paragraph 1:

No one shall be held guilty of any criminal offence on account of any act or omission which did not constitute a criminal offence under national or international law at the time when it was committed. Nor shall a heavier penalty be imposed than the one that was applicable at the time the criminal offence was committed

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    The only exception to that is crime against humanity. The notion did not exist during World War II and was established afterwards.
    – Clockwork
    Commented Oct 19, 2023 at 7:14
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    @Clockwork But that was before the ECHR came into force, no? Commented Oct 19, 2023 at 11:00
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    So I guess the ECHR's prohibition on retrospectively criminalizing stuff is itself not retrospective. That's quite a pleasing symmetry. Commented Oct 19, 2023 at 11:14
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    That last comment is quite interesting actually, because in some countries (France for example), you can retroactively benefit from lessened penalty if you were judged for an offence you committed before the new law came around.
    – Clockwork
    Commented Oct 19, 2023 at 11:20

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