Where the 17c Formula Actually Comes From
The 17c formula is often described as if a court simply invented "the" diminished-value formula. That's not accurate, and getting the history right matters for how much weight to give the number. In 2001, the Georgia Supreme Court held in State Farm Mutual Automobile Insurance Co. v. Mabry, 274 Ga. 498, 556 S.E.2d 114 (Ga. 2001), that Georgia law requires insurers to evaluate and, where applicable, pay first-party policyholders for diminished value after a covered repair — not just the repair cost itself. The Court did not hand down a specific calculation formula.
Because the underlying litigation involved a class of more than 25,000 claimants whose vehicles could not practically be individually appraised, the Superior Court of Muscogee County approved a generic formula — a 10% base-value cap adjusted by a damage-severity multiplier and a mileage multiplier — in a 2002 class-settlement order, as a practical mechanism for resolving that specific class action. It was a settlement shortcut for a mass-claims situation, not a scientifically validated method for any individual vehicle, and not authored by the Supreme Court itself.
In December 2008, Georgia's insurance regulator (the Office of Insurance and Safety Fire Commissioner, Directive 08-P&C-2) stated that the Department had not approved any specific formula for calculating diminished value and that carriers should not represent to insureds that it had. Despite that, the same general calculation structure has spread well beyond Georgia and beyond the case it came from, often presented by insurers as a standard worksheet without that history attached.
This tool uses the commonly-published version of that formula — a 10% base-value cap, a damage-severity multiplier, and a mileage multiplier — because it's the version most claimants are likely to encounter on an insurer's own worksheet. It is shown here with its actual origin attached and labeled as a baseline for comparison, never as your vehicle's legally correct diminished value.
How the Calculation Works, Step by Step
The result above is built from three steps, each shown with your actual numbers substituted in:
Step 1 — Base loss assumption: the pre-accident value is multiplied by a flat 10%, which becomes the maximum this baseline can ever produce, regardless of how severe the damage was.
Step 2 — Damage-severity modifier: that 10%-cap figure is multiplied again by a modifier from 0.00 (cosmetic-only, no structural involvement) to 1.00 (severe structural or frame damage), reflecting how much of a resale stigma that category of damage is assumed to carry.
Step 3 — Mileage modifier: the result is multiplied a third time by a mileage-based factor that steps down from 1.00 at low mileage to 0.00 at 100,000+ miles — the idea being that a high-mileage vehicle's value is already discounted, so accident history adds proportionally less additional stigma.
Why the Market Evidence Worksheet Is Kept Separate
The 17c-style baseline uses a fixed formula that doesn't know anything about your specific local market, vehicle segment, or actual buyer behavior — a national guide value multiplied by generic percentages, no matter the car. Real comparable sales — actual listings or sale prices for similar vehicles with and without disclosed accident history — reflect what buyers are actually paying right now, in your area, for a vehicle like yours. Neither method is automatically more correct: the formula is transparent and consistent but generic, while comps are specific but harder to gather reliably and can vary with how carefully they're matched. Showing both, clearly labeled, side by side, is more honest than picking one and calling it "the" answer — or worse, quietly averaging two numbers that were never meant to be combined.