The 17c formula and why it isn't California law

General information, not legal advice. This site is not a law firm and does not provide legal services. Check the linked sources and talk to a licensed professional about your situation.

The short version

"17c" is a shortcut formula some insurers use to put a number on diminished value.
It came out of Georgia court cases in the early 2000s, not California law.
We found no California statute or regulation that adopts 17c. California courts measure lost value by fair market value before and after (CACI No. 3903J).
Your offer doesn't have to be the last word. You can answer it with real market evidence.

How the formula works

Georgia court documents describe these pieces:

Start with the car's pre-accident value from a pricing guide (the State Farm letter quoted below uses "NADA Value").
Cap it at 10% of that value. That 10% becomes the starting point, the most the formula can produce.
Multiply by a "damage severity modifier," a percentage based on how bad the damage was. A Georgia appeals court described it as a "subjective decision, which must be made by the adjuster."
Multiply by a mileage modifier, a percentage based on the car's mileage.

Made-up example (illustration only, not real data): Pre-accident value $30,000 → 10% cap = $3,000 → damage modifier 0.50 = $1,500 → mileage modifier 0.60 = $900.

Because every step can only cut the number, 17c results are often small. In one real State Farm letter shared online by a Georgia appraisal company, the result was $41.84 on a car valued at $19,925. The letter shows 10% of value, a 10% damage modifier, and a 21% mileage modifier. (letter PDF. It's hosted by a private company, so treat it as an example, not an official record.)

Where it came from (what we could verify)

State Farm v. Mabry (Georgia Supreme Court, 2001). The court held that State Farm's Georgia policies required it to pay for lost value when repairs don't bring the car back to its pre-loss value, and to assess that loss when a policyholder makes a claim. Citation: State Farm Mut. Auto. Ins. Co. v. Mabry, 274 Ga. 498 (2001). Opinion on Justia
The formula itself came from court orders in Georgia litigation, not from the Supreme Court opinion. The State Farm letter above quotes a March 6, 2002 order of the Muscogee County trial court in Mabry that calls it "the 17(c) formula included in the June 12, 2001 order." It approves it as "an acceptable methodology" for State Farm's Georgia claims.
The Georgia Court of Appeals later wrote that the "so-called '17 (c)' formula is named after paragraph 17 (c) of the second injunction" in a related Georgia class action, Walker v. American National General Insurance Co. Amica Mut. Ins. Co. v. Sanders (Ga. Ct. App. 2015). Opinion on Justia
The same 2015 opinion quotes a 2008 directive from Georgia's Insurance Commissioner: the department "has not endorsed a particular formula or method," and "total reliance on one particular formula or method ... may not be appropriate."

So the common shorthand "17c comes from Mabry" is roughly right. The more precise version: it came out of court orders in the Georgia litigation around Mabry, and the sources don't agree on which order it first appeared in. Even Georgia's own regulator said no formula is the final word.

What California uses instead

California's rule comes from general damages law, not a formula:

Civil Code §3333: compensation "for all the detriment proximately caused." leginfo
CACI No. 3903J: if a repaired car is still worth less, the damages are repair cost plus the difference between its value right before the harm and its value right after repairs, capped at the pre-harm value. "Fair market value" is "the highest price that a willing buyer would have paid to a willing seller," with both knowing the relevant facts about the car's condition. CACI 3903J

That's a market test: what would real buyers pay? A 10% cap and adjuster-picked multipliers aren't part of it.

What to do if your offer was calculated with 17c

Ask the adjuster in writing how they got their number, and ask for the worksheet.
Get market evidence. An independent diminished-value appraisal is the usual way.
Independent diminished-value appraisal services exist. If you hire one, check the appraiser's credentials and make sure you get a written report.
Send a written demand with that evidence. Use our demand letter template.
Know the timelines. California insurers generally must respond to a claimant's communication within 15 calendar days (10 CCR §2695.5(b)). CDI regulations index
Fallbacks: a CDI complaint, or small claims against the at-fault driver (up to $12,500 for individuals). California Courts

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Published 2026-10-24 · Last reviewed October 2026