Comparative fault—also known as comparative negligence—is a rule of tort law for allocating liability when two or more parties to an accident or liability incident are at least somewhat at fault.

For example, in a case in which both the plaintiff and the defendant were negligent, the jury may be asked to apportion the liability or responsibility for the accident (and the resulting damages) between the parties—usually as a percentage of each party's negligence—and the plaintiff’s recovery against the defendant may be offset or reduced by the amount of the plaintiff’s negligence. This rule may be referred to as pure comparative fault.

Other states have enacted a modified comparative fault statute or law that reduces a plaintiff’s recovery by the plaintiff’s percentage of fault, but bars a plaintiff from any recovery if the plaintiff is 50% or more at fault for the cause of the accident.

And in South Dakota, the comparative fault system uses a slight/gross negligence system and only analyzes the comparative fault if the plaintiff’s negligence is slight and the defendant’s negligence is gross. Under this slight/gross negligence system, if the plaintiff’s negligence is more than slight and the defendant’s negligence is less than gross, the plaintiff is barred or prohibited from any recovery.

Comparative fault laws vary from state to state and may change or evolve at any time—whether they are located in court opinions or in statutes.

In Florida, the rule of comparative fault, also known as comparative negligence, is applied in cases where multiple parties share responsibility for an accident or injury. Under Florida law, specifically Florida Statutes section 768.81, the state follows a pure comparative negligence system. This means that if a plaintiff is found to be partially at fault for their own injuries, their compensation will be reduced by their percentage of fault. For example, if a plaintiff is awarded $100,000 in damages but is found to be 20% at fault, the actual recovery would be $80,000. Unlike modified comparative fault states, there is no threshold in Florida that bars recovery if the plaintiff's fault reaches a certain percentage. Even if the plaintiff is found to be 90% at fault, they can still technically recover the remaining 10% of their damages from the other at-fault party. This system allows for a fair distribution of damages based on the degree of fault attributed to each party involved in the incident.