An impairment rating is a percentage that represents how much permanent physical function you’ve lost due to an injury or illness. Defined by the American Medical Association as “a loss, loss of use or derangement of any body part, organ system or organ function,” the rating translates your lasting medical limitations into a number that determines what benefits or compensation you’re entitled to. If you’re going through a workers’ compensation claim, a personal injury case, or a federal benefits program, this number carries real financial weight.
Impairment vs. Disability
These two terms sound interchangeable, but they mean very different things in legal and medical contexts. An impairment rating measures the physical or mental function you’ve lost, period. It doesn’t consider your age, your job, your education, or whether you can still work. A 15 percent whole-person impairment rating means the same thing whether you’re a desk worker or a construction laborer.
Disability, by contrast, factors in your ability to earn a living. The Social Security Administration defines disability as “the inability to engage in substantial gainful activity” due to a medical condition expected to last at least 12 months or result in death. That’s a much broader question than what an impairment rating answers. Workers’ compensation systems often use your impairment rating as a starting point, then layer on vocational factors to arrive at a disability determination. So your impairment rating is one ingredient in the larger disability calculation, not the whole recipe.
When You’re Eligible for a Rating
You can’t receive an impairment rating while you’re still recovering. First, you need to reach what’s called Maximum Medical Improvement, or MMI. This is the point where your doctor determines that further treatment won’t significantly improve your long-term condition. It doesn’t mean you’re fully healed. It means your recovery has plateaued.
Your doctor makes this call based on several factors: regular checkups tracking your healing, diagnostic imaging like X-rays or MRIs showing whether tissues have stabilized, range-of-motion and strength testing, your ongoing pain and symptom reports, and your response to treatments like surgery or physical therapy. If you’ve tried multiple interventions without seeing further progress, that’s a strong signal you’ve reached MMI.
Once your doctor confirms MMI, the next step is evaluating whether you have any lasting loss of function. That evaluation produces your impairment rating.
How the Rating Is Determined
The standard reference for impairment ratings in the United States is the AMA Guides to the Evaluation of Permanent Impairment. The federal government has used standardized AMA tables for this purpose for more than 50 years, dating back to the first guide published in 1958. The Sixth Edition, adopted by the Division of Federal Employees’ Compensation in 2009, is the current standard for federal claims, though some states still require earlier editions.
The rating percentages reflect the severity of your condition and how much it reduces your ability to perform common activities of daily living, like walking, gripping, bending, or lifting. During the evaluation, a physician typically assesses range of motion, neurological function, pain levels, and any measurable loss of strength or sensation. For specific conditions, the evaluation may also consider factors unique to that injury. A breast cancer impairment evaluation, for instance, would look at upper-extremity function, neurological abnormalities, lymphedema, and pain.
The rating can be performed through an in-person examination or, in some cases, by a consulting physician who reviews your medical records and daily-living questionnaires without seeing you in person. Either way, your complete medical history, imaging results, and treatment records are essential to an accurate rating.
Whole-Person vs. Regional Ratings
Impairment ratings come in two forms. A regional or extremity rating measures the loss of function in a specific body part, like your shoulder or knee. A whole-person impairment (WPI) rating expresses that same loss as a percentage of your total body function. For example, a significant hand injury might rate at 40 percent of the hand but convert to a much smaller whole-person percentage, because your hand represents only a fraction of your overall physical capacity.
Which type of rating matters depends on your claim. Workers’ compensation schedule awards for specific body parts often use regional ratings. Claims involving multiple injuries or conditions affecting your overall function typically use whole-person ratings.
Combining Multiple Ratings
If you have impairments in more than one body part, the numbers don’t simply add up. A 20 percent rating plus a 10 percent rating does not equal 30 percent. Instead, the AMA Guides use a combined values formula: the second impairment is applied only to the remaining unimpaired portion of your body. The formula works like this: A + B × (1 − A), where A and B are the decimal versions of each rating.
So for a 20 percent and a 10 percent impairment, the math is 0.20 + 0.10 × (1 − 0.20) = 0.20 + 0.08 = 0.28, or 28 percent combined. The logic is straightforward: if you’ve already lost 20 percent of your function, the second impairment can only affect the remaining 80 percent. This combined values approach applies no matter how many separate impairments you have; you just keep combining them two at a time.
How the Rating Affects Your Benefits
Your impairment rating directly influences how much compensation you receive. In workers’ compensation, a higher percentage generally means a larger lump-sum payment or more weeks of benefits. The exact dollar amount varies widely by state, by the body part affected, and by your pre-injury wages. Under certain federal programs, there are caps. The Department of Labor’s Energy Employees program, for example, sets a maximum of $250,000 in combined wage-loss and impairment benefits, excluding medical costs.
In personal injury lawsuits, the impairment rating serves as evidence of permanent harm. It gives juries and insurance adjusters a concrete number to work with when calculating damages. Even a few percentage points can mean a significant difference in your settlement or award.
Preparing for Your Evaluation
The most useful thing you can do before an impairment rating exam is gather your complete medical documentation. Bring records of every treatment you’ve received for the injury: surgical reports, physical therapy notes, imaging results, and medication history. If your evaluator is reviewing records rather than examining you in person, you’ll likely need to complete a detailed questionnaire about your daily activities and functional limitations.
Be honest and specific during the exam. If certain movements cause pain, say so, but don’t exaggerate. Evaluators are trained to identify inconsistencies between your reported symptoms and objective findings. Describe your limitations in practical terms: what you can’t do at home, what activities you’ve had to give up, and how your injury affects routine tasks like dressing, cooking, or driving.
If you disagree with the rating you receive, most systems allow you to request a second opinion or file a dispute. Impairment ratings involve medical judgment, and two qualified physicians can reasonably arrive at different numbers based on the same condition. Knowing that the process isn’t always final on the first pass can help you advocate for an accurate result.