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 Iowa, the rule of comparative fault, also known as comparative negligence, is used to allocate liability among parties who are both at fault in an accident or incident. Iowa follows a modified comparative fault system. Under this system, a plaintiff's recovery is reduced by their percentage of fault. However, if the plaintiff is found to be 50% or more at fault for the accident, they are barred from recovering any damages from the defendant. This means that a plaintiff must be less than 50% responsible for their own injuries to receive compensation from other at-fault parties. Iowa's comparative fault rules are codified in state statutes and can be subject to change, so it is important to consult with an attorney for the most current legal guidance.