Police deal with false criminal accusations with relative frequency. It is an unfortunately regular occurrence for people going through bitter divorces, particularly when it comes to child custody. However, the penalties for falsely accusing someone of a crime range from none at all to potentially decades behind bars. It all depends on how the accusation is made, the intent of the accuser, and what is being accused.
It should be clear that a person who accidentally makes a false accusation to police is unlikely to face any criminal penalty at all. A person will not face criminal prosecution if they, in good faith, report someone they believe has committed a crime. But if the accuser has no reasonable basis to believe a crime has been committed, then they may be wandering into the false accusations territory where criminal (and civil) liability could exist.
Intentional False Accusations
Nearly every jurisdiction has some criminal statute that makes it a misdemeanor to knowingly provide a false report to law enforcement. In addition to the misdemeanor, which could land a person in jail for up to one year, intentionally making false accusations to the police results in potential civil liability.
Apart from the emotional distress, and life disruption, caused by a false report, because the act is intentional, the accuser could be on the hook for punitive damages, in addition to compensatory damages. Punitive damages are monetary awards that are designed to punish wrongdoers, rather than compensate victims for their losses.
Terrorism Accusations and Swatting
If the false accusations involve terrorism, or "swatting" (accusations of an immediate threat necessitating a SWAT team or a similar response from law enforcement), then a false accuser will likely be looking at felony charges. These types of false accusations are punished more severely because of the risk of the accused's civil rights being violated is much higher, as well as the waste of public resources is much greater. In fact, under federal law, false accusations regarding terrorism can be punished by up to two decades in jail.
Lastly, it should be noted that if false accusations of criminal conduct are just made publicly, and not to police, then an individual is highly unlikely to face any criminal charges. However, in a civil case, under defamation law, false accusations that a person committed a crime tend to be easier to prove.