The four categories
Workers' comp sorts every injury into one of four buckets, and the bucket determines both the size and the duration of benefits:
- Temporary total (TTD): you cannot work at all, but you are expected to recover. Pays the standard weekly formula while you heal.
- Temporary partial (TPD): you can work some — reduced hours or light duty at lower pay. Pays a fraction of the wage gap.
- Permanent partial (PPD): you healed as much as you will, but a measurable impairment remains — the most common permanent category.
- Permanent total (PTD): you cannot perform sustained work at all. Benefits can run for life or to retirement age, depending on the state.
The hinge: maximum medical improvement
The pivot from temporary to permanent is MMI — the point where your treating physician concludes that further recovery is not expected. MMI does not mean healed; it means plateaued. Temporary wage benefits end there, and the case converts to a question with a price tag: how much function did you permanently lose?
How a rating becomes dollars
At MMI a physician assigns an impairment rating — a percentage of whole-person loss, calculated under the medical guide your state has adopted (many use the AMA Guides; several, including California, layer their own adjustments on top). The rating then passes through the state's schedule: each state publishes a formula converting the percentage, the body part, your wage, and sometimes your age and occupation into a number of weeks of benefits at your weekly rate. A 10% rating might convert to 30 weeks in one state and a very different figure in another — the rating is medical, but the conversion is pure state law.
Disputing the rating
Ratings are the most-litigated number in workers' comp because small percentages compound across weeks of benefits. If the insurer's examining physician returns a rating your own doctor considers low, every state offers a dispute path — typically an independent medical examination and a hearing before a workers' comp judge. Before accepting a lump-sum settlement that closes future medical care, model the scheduled value with the Workers' Comp Settlement Calculator and have a licensed attorney compare the offer against it.
One injury, four phases: a worked example
A machinist herniates two lumbar discs at work. Weeks 1–6: totally off work — TTD at the statutory fraction of his average weekly wage (say $767, subject to the state ceiling — see state maximums). Weeks 7–16: released to light duty at $400 less per week — TPD covers a fraction of that $400 gap. Week 16: the surgeon declares maximum medical improvement. Temporary benefits end that week — including the light-duty supplement — and the claim becomes a rating question. After MMI: the physician assigns an impairment rating; suppose the state's schedule converts the resulting back-impairment percentage into a fixed number of compensable weeks. Those weeks × his weekly rate = the scheduled PPD award. Hypothetical throughout — the rating, the conversion, and the ceiling are all state-specific — but the sequence is universal: wage benefits first, the pivot at MMI, then the permanent schedule.
Scheduled members and the body as a whole
Permanent-partial systems split into two architectures, and the difference matters. Under a scheduled-award approach, losing specific body parts pays a fixed number of weeks per member — a hand, a leg, an eye — regardless of how the loss affects your particular job. Unscheduled (body-as-a-whole) systems convert whole-person impairment percentages into weeks, and some states layer a wage-loss analysis on top: if the impairment demonstrably reduced your earning capacity, benefits follow the wage loss rather than the medical percentage alone. A hand injury that ends a surgeon's career prices very differently under these architectures — which is why comparing your "rating" against someone else's across state lines is meaningless.
When MMI feels premature
MMI is a medical opinion, and opinions can be contested — but only through the state's process. If your physician would not have declared the plateau, the remedy is a documented second opinion or the state's dispute mechanism (independent medical examination, commission review), before the case converts to settlement, not after. Two practical failures to avoid: accepting an MMI letter you never discussed with your own doctor, and treating a re-rating request as optional — in most systems, benefits that flow from the rating (and the window to challenge it) run on clocks. The state-by-state dispute paths and their quirks are the domain of state comp rules.
The settlement decision at MMI
Permanent-partial cases often resolve by lump sum, and the trade is always the same: certain money now versus scheduled benefits and — in many states — open future medical care for the accepted condition. Closing future medical is the insurer's main source of value in a compromise-and-release; if your condition might worsen (a fused segment adjacent to the injury, a knee replacement in your future), that open card may be worth more than the lump-sum premium being paid for it. Price both halves — the scheduled weeks and the actuarial value of open medical — before deciding. This is the classic point where a one-hour attorney consult pays for itself many times over.