The 17c Formula: Why the Insurer's Diminished Value Offer Is So Low

How the formula works

The 17c calculation runs in three steps. Start with the vehicle's book value (typically NADA retail). Take 10% of it — that is the most the formula will ever allow, no matter how severe the damage. Then multiply by a damage modifier from 1.00 down to 0.00 (1.00 for severe structural damage, 0.75 major, 0.50 moderate, 0.25 minor, 0.00 for replaced panels with no structural damage). Then multiply again by a mileage modifier that falls from 1.00 at zero miles to 0.00 at 100,000 miles.

A worked example

Take a $30,000 SUV with major structural damage and 60,000 miles — a serious collision by any standard:

• 10% cap: $30,000 × 0.10 = $3,000 maximum, before reductions
• × 0.75 damage modifier (major structural) = $2,250
• × 0.40 mileage modifier (60,000 miles) = $900

Nine hundred dollars — on a vehicle that may have taken $20,000 in structural repairs and, by market evidence, commonly loses several thousand dollars in resale value from the permanent accident record. And under the same formula, any vehicle over 100,000 miles receives exactly $0, regardless of damage.

Where "17c" actually comes from

The name refers to paragraph 17(c) of a claims-procedure filing that State Farm submitted in Mabry v. State Farm, a 2001 Georgia Supreme Court case. Two facts about that origin matter. First, Mabry was a first-party Georgia case — about what State Farm owed its own policyholders — not a ruling on what any at-fault insurer owes you in a third-party claim. Second, the formula was one company's proposed administrative method in one state's litigation. No court and no legislature has ever adopted it as the required way to measure diminished value, and Georgia's Insurance Commissioner has explicitly stated that the office neither produced nor endorsed any formula for determining diminished value. Yet adjusters across the country cite it as if it were law.

The three flaws

The 10% cap is arbitrary. No market data supports the idea that a vehicle cannot lose more than 10% of its value to accident history. Actual comparable-sales data routinely shows accident-history vehicles selling at 10–15% discounts for an accident record alone, and repaired structural damage placing the loss substantially higher.

The damage modifier is subjective. The adjuster — the party paying the claim — chooses the multiplier that shrinks it. There is no published standard for what makes damage "moderate" versus "major."

The mileage modifier double-counts. Book value already reflects mileage — a 60,000-mile vehicle is already worth less than a 20,000-mile one before the formula starts. Reducing the claim again for the same mileage counts the same factor twice, and zeroes out every vehicle past 100,000 miles — vehicles that demonstrably still lose real money to accident history in the resale market.

What answers it: market evidence

A formula not tied to your specific vehicle's market data does not rebut market evidence. An independent appraisal built on comparable sales — what clean-history vehicles of your exact year, trim, and drivetrain actually list for versus accident-history vehicles of the same configuration — measures the loss the market actually imposes, rather than the loss a payer's worksheet allows. That is the standard a court applies too: proof of the actual difference in fair market value, not a claims-department formula. (For the full method, see our guide on how to recover diminished value.)

How to respond to a 17c offer

1. Recognize it. If the offer arrived fast, is a suspiciously round fraction of your car's value, or the adjuster mentions "our formula," you are likely looking at 17c output.
2. Ask for the basis in writing. Request the calculation, each modifier used, and the justification for each. Formulas survive poorly in writing.
3. Answer with market evidence. A comparable-sales appraisal of your specific vehicle. Ask the insurer to identify which comparables or figures they dispute — a general "we use a formula" does not respond to evidence.
4. Don't accept the opening number. The first 17c figure is an opening position, and insurers expect most claimants to take it and go away. The ones who answer with documentation are the ones who move the number.
5. Keep small claims in reserve. A credible signed appraisal carries real weight with a judge — and insurers know it.