Most acute injuries and illnesses resolve, ie, reach maximum medical improvement (MMI), within days or weeks and without permanent impairment. Fractures, more severe soft tissue injuries and illness, and conditions that require surgery take longer to reach MMI, often about a year, with a range of six months to two years. Serious head, spinal cord, and other catastrophic injuries commonly take two or more years to reach MMI. These more severe injuries and illnesses understandably are more likely to result in permanent impairment. However, various parties to the claim process may request impairment rating prematurely: The claimant or plaintiff whose injury or illness has resulted in loss of income and financial hardship may push for an early impairment award or settlement. The surgeon who has operated and is done with postoperative follow-up may want to be rid of claim forms and move on to other patients. The overburdened adjuster may want to get the claim closed, thereby diminishing their workload. But rating impairment prior to MMI, ie, before it is permanent, often results in erroneously inflated ratings. In general, functional status, physical findings, and/or clinical study results improve over time, sometimes with and sometimes without treatment. This usually results in a concurrent decrease in, and sometimes even resolution of, impairment. With knowledge of the appropriate terminology and definitions, the evaluating physician should be able to render an opinion regarding MMI that is both understandable and legally sustainable in the applicable jurisdiction.