A medical percentage that measures the lasting loss of bodily function after an injury or illness.

"Medical" means it is assigned by a qualified clinician, not by the injured person, employer, or insurer. "Percentage" means the loss is converted into a number, usually from 0% to 100%, so the severity of permanent damage can be compared across cases. "Lasting" means the condition has reached maximum medical improvement or is otherwise stable enough to estimate permanent effects. "Loss of bodily function" focuses on what the body can no longer do normally - such as grip strength, range of motion, nerve function, vision, hearing, or tolerance for repetitive use - not simply how much pain is reported.

In practice, an impairment rating is often used to support a claim for permanent partial disability or other long-term benefits. A higher rating can increase the value of a case, but it is not the same as disability. Impairment measures physical or mental loss; disability addresses how that loss affects work and daily earning capacity.

In Hawaii workers' compensation, impairment evidence can directly affect permanent disability awards under Hawaii Revised Statutes § 386-32 (2024). Disputes often center on which doctor performed the evaluation, whether the worker had actually reached maximum medical improvement, and whether the rating properly accounts for repetitive-stress injuries, restricted motion, nerve damage, or surgical changes. An incorrect rating can reduce benefits or delay settlement.