By Jessica Martinez, Contributing Writer, Business & Finance · Updated 2026-07-09
A car that gets fixed after a wreck is still worth less than an identical car that was never in one. That gap is diminished value, and the most common way insurers and appraisers put a dollar figure on it is a method known as the 17c formula: a fixed base loss, cut down by how bad the damage was and how many miles are on the odometer.
What the 17c formula actually multiplies
The math has three moving parts. First, a base loss equal to a flat percentage of the car's pre-accident value, almost always 10 percent, pulled from a guide like NADA. Second, a damage multiplier between 0.00 and 1.00 that scores how structurally serious the repair was: no structural damage scores 0.00, severe structural damage scores 1.00, with quarter-point steps in between for moderate and major damage. Third, a mileage multiplier, also between 0.00 and 1.00, that shrinks the estimate as the odometer climbs, on the idea that a high-mileage car had less remaining value to lose in the first place. The three numbers are multiplied together, not added, so a low score on any single factor drags the whole estimate down fast.
The scales below are the ones used in the worksheets appraisers publish alongside the formula, including the breakdown at 17cformula.com. Values between the listed points are interpolated in a straight line, which is exactly what the calculator above does at 45,000 miles to land on a 0.55 mileage multiplier.
| Damage description | Multiplier |
|---|---|
| No structural damage, panels replaced only | 0.00 |
| Minor structural damage | 0.25 |
| Moderate structural or panel damage | 0.50 |
| Major structural or panel damage | 0.75 |
| Severe structural damage | 1.00 |
| Mileage at time of loss | Multiplier |
|---|---|
| 0 miles | 1.00 |
| 20,000 miles | 0.80 |
| 40,000 miles | 0.60 |
| 60,000 miles | 0.40 |
| 80,000 miles | 0.20 |
| 100,000 miles or more | 0.00 |
Where the formula came from
The 17c formula did not start as an industry standard. It came out of State Farm Mut. Auto. Ins. Co. v. Mabry, a 2001 Georgia Supreme Court decision (274 Ga. 498, 556 S.E.2d 114) that held insurers owe diminished value on first-party collision claims even when repairs are done correctly. That ruling opened the door to a class action covering roughly 25,000 Georgia policyholders, and in 2002 the Superior Court of Muscogee County approved a generic settlement formula, a 10 percent loss cap adjusted by damage and mileage, so the claims could be processed in bulk instead of appraised one by one. That settlement math is what the industry now calls 17c.
It was built to close one lawsuit, not to value individual cars precisely. Georgia's own Department of Insurance later stepped back from it too. According to the personal injury firm Red Rock Injury Law, the department told carriers in 2008 to stop suggesting that the state had approved any particular diminished-value formula.
Why appraisers argue about it
The formula has been in wide use for two decades, but that does not mean appraisers consider it accurate. According to Diminished Value of Georgia, a firm that appraises post-accident vehicles for a living, the method has a few recurring problems:
- The 10 percent base is not tied to any market study; it is simply the number the 2002 settlement order used.
- Vehicle guide values used as the starting point are national averages, so they can miss local supply and demand swings.
- The damage multiplier scores structural severity, not how a buyer actually reacts to a car's accident history, which do not always line up.
- Vehicle guide values already discount for mileage, so applying a second mileage multiplier can double-count the same loss, and cars past roughly 100,000 miles often calculate out to zero.
Does your state accept it?
No state requires insurers to use 17c. It has no statute or regulation behind it outside the Georgia settlement that produced it, and courts elsewhere have not adopted it either. Plenty of adjusters still reach for it as a quick starting number because it is familiar and easy to calculate, but an independent appraiser working your claim, or the insurer's own desk adjuster, may land somewhere else entirely using comparable sales, wholesale-retail spreads, or another accepted appraisal method.
Worked example, step by step
Pre-accident value: $24,000. Base loss cap: 10%, so base loss = $24,000 x 0.10 = $2,400.
Damage: major structural repair, multiplier 0.75.
Mileage: 45,000 at the time of the accident. That falls between the 40,000-mile mark (0.60) and the 60,000-mile mark (0.40), a quarter of the way across, so the interpolated multiplier is 0.60 minus a quarter of 0.20, or 0.55.
Diminished value = $2,400 x 0.75 x 0.55 = $990.
Change any one input and the answer moves fast. Drop the mileage to zero and the same car and damage level comes out to $1,800. Push the damage down to minor (0.25) and it falls to $330.
Limitations worth knowing
This is a planning estimate, not a claim valuation. Real settlements depend on which insurer is paying, which state you are in, and whether an independent appraiser gets involved. Where you can even file this kind of claim varies too: some drivers pursue it against their own insurer, but far more success comes from pursuing it against the at-fault driver's insurer, since first-party policies are not always written to cover it. And if the repair estimate is high enough that fixing the car does not make economic sense in the first place, diminished value is not the number you need; check whether the car crosses the line into a total loss instead.
Coverage rules add another wrinkle. Many personal auto policies do not clearly promise to pay diminished value on your own claim, so drivers often have better luck filing against the at-fault driver's liability insurer, where the legal duty tends to be more settled. If your own insurer denies the claim outright, an independent appraiser or a local attorney who handles these claims regularly can usually tell you within a phone call whether pursuing it further is worth the time.