17c Diminished Value Calculator
The "17c formula" is how most insurers calculate diminished value after an accident. This calculator computes it exactly as published — then explains why the result is best understood as the insurer's opening position, not your car's actual loss in value.
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How the formula works
The 17c formula comes from a 2001 Georgia class-action settlement (Mabry v. State Farm), where it appeared as paragraph 17(c) of the claims-handling exhibit. It was never a study of actual resale outcomes — but it spread industry-wide because it is cheap to apply and produces small numbers. It computes:
| Step | Rule |
|---|---|
| 1. Base loss cap | 10% of the vehicle's pre-accident value |
| 2. Damage modifier | ×0.00 to ×1.00 by damage severity |
| 3. Mileage modifier | ×1.00 under 20k miles, stepping to ×0.00 at 100k |
What 17c systematically leaves out
- The 10% cap is arbitrary. Market data on rebuilt and accident-history vehicles routinely shows stigma discounts well beyond 10% of pre-loss value, especially for newer and higher-value vehicles.
- Mileage is double-counted. Mileage already reduced your car's pre-accident value in step 1; the formula then discounts the loss again for the same miles.
- 100,000+ miles ⇒ $0 by definition. The formula assumes high-mileage vehicles cannot lose value from an accident history. Resale data does not support that.
- It ignores what actually happens at resale. Actual diminished value is the gap between what comparable clean-history vehicles sell for and what yours will — a measurable market quantity, not a three-factor worksheet.
If the 17c number and your own sense of the loss are far apart, that gap is the reason independent appraisals and market-data-based estimates exist. Many states allow diminished value claims against the at-fault driver's insurer; deadlines and rules vary by state.
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