Diminished Value Calculator: How the 17c Formula Works (and Why It's Low)

Let’s be honest about how that offer felt. You open the letter, you see a few hundred dollars for a car that any buyer can now see was wrecked, and something in your gut says that can’t be right. Your gut is correct. Even a flawless repair doesn’t erase what a car loses just for having an accident on its record. That lost resale value is called diminished value, and 17c is the formula insurers use to decide what it’s worth. The whole thing is quietly engineered to land low, and it keeps working for one simple reason: almost nobody pushes on it. You’re about to, and it’s easier than it sounds.

First, run 17c on your own car

Don’t take my word for any of this. Watch the formula do its thing. Punch in your car’s details and you’ll see the insurer’s likely number sitting right next to what an independent appraiser would probably say.

See that gap? It looks official enough that most people just sigh and accept it. But there’s nothing official about it — and once you know how the number gets built, you won’t be able to take it seriously.

Why 17c always comes out so small

The formula quietly does three things to your car, step by step:

1. It caps your loss at 10%. Doesn’t matter how badly the car was hurt; 17c just decides, up front, that you couldn’t possibly have lost more than 10% of what the car was worth. That ceiling alone tosses out most of the real damage to your wallet.
2. Then it shaves that down for the damage. That 10% gets multiplied by a “severity” number. Moderate damage? You keep half. Just like that, half of an already-shrunken number is gone.
3. And then it shaves it again for mileage. Whatever survived gets multiplied a second time. Roll past 100,000 miles and that multiplier is a flat zero.

So it’s a hard 10% cap, then two more cuts stacked on top of that. That’s the whole trick — it’s how a car that genuinely lost $3,500 ends up at $500.

Run the calculator’s own starting numbers by hand and you can watch every cut land. A $25,000 car, moderate damage, 40,000 to 59,999 miles on it at the time of the wreck: 10% of $25,000 is $2,500. Moderate damage keeps half of that, so $1,250. That mileage bracket keeps 60% of what’s left, so $750. Enter those same three numbers above and the calculator hands back exactly $750, because it’s running the identical math. An independent appraiser working from real comparable sales would likely put that same car’s loss at $2,500 to $6,250. The formula and the market are pricing the same wreck. They just don’t agree on the number.

Where the 17c number actually comes from

17c isn’t a law, and no regulator wrote it. It comes from one lawsuit. In 2001, the Georgia Supreme Court ruled on a case called State Farm Mutual Automobile Insurance Co. v. Mabry and told the industry something it didn’t want to hear: even a repair that looks perfect doesn’t erase the value a car lost, and State Farm owed its own policyholders for that loss, not just people its drivers had hit.

That ruling turned into a class action covering State Farm’s Georgia policyholders. To settle that many claims at once, somebody had to put a number on a huge batch of cars without appraising each one by hand. So in 2002, the Superior Court of Muscogee County, the trial court handling the settlement, wrote a shortcut formula directly into its order. Section (c) of paragraph 17 is where the 10% cap and the two multipliers actually live. That paragraph number is the entire reason anyone calls this “17c.” It was built to close out one lawsuit fast. Nobody designed it to price your car correctly.

Georgia’s own insurance regulator has said as much. In December 2008, then-Commissioner John Oxendine told insurers in writing that his department had never written or approved any diminished value formula, 17c included, and that they needed to stop presenting it as the final number. That was more than fifteen years ago. Most insurers still run it, because it’s free, it’s fast, and it favors them.

17c is a floor, not the final word

That number is not a legal ceiling on what you can recover. No state law adopts it. No court outside the original Mabry settlement has ever been bound by it. Technically, it applies only to the State Farm policyholders covered by that 2002 Georgia settlement. Everyone else who sees “17c” on an insurer’s worksheet is looking at a voluntary industry habit, not a rule anyone has to follow.

It undersells you hardest in a few situations: a newer car with low mileage and real structural damage, where the 10% ceiling still caps your number no matter how much an appraisal would actually find; a car in a market where buyers punish accident history hard on resale; or a claim where the adjuster never ran the math at all and just handed you a small number with “17c” attached to make it sound official.

An independent appraisal isn’t capped at 10% of anything. It starts from real sales, cars like yours, some with an accident on the record and some without, and reports the actual gap between them. That’s the number that survives a demand letter, a state insurance complaint, or a judge. Our appraisal guide covers what one costs in 2026 and which credentials on an appraiser’s website actually mean something.

Does 17c change from state to state?

The formula itself doesn’t. Wherever you are, an insurer running “17c” is doing the same 10% cap, the same damage cut, the same mileage cut the Muscogee County court wrote into its order in 2002. What changes state to state is everything around it: whether you can file a diminished value claim at all, how long you have to file it, and how hard your state pushes back when insurers lowball.

Georgia is where this started, and Georgia still gives its own drivers the strongest rights in the country: you can file against your own insurer, not just the other driver’s, and a badly handled claim can expose the insurer to a bad-faith penalty of up to 50% of the claim (or $5,000, whichever is greater) plus your attorney fees, on top of what they already owed you. Our Georgia guide covers the specifics.

We’ve mapped the rules in detail for Texas, California, Florida, and Virginia, North Carolina, and Colorado. If your state isn’t on that list, say you found this page searching for the Maryland formula, the math above is exactly what your insurer is running on your car too. Maryland doesn’t have its own version of 17c or its own diminished value statute. What is specific to Maryland: it’s one of the few states left running pure contributory negligence, so carrying even a small share of the blame can bar you from recovering diminished value at all. Property-damage claims generally carry a 3-year deadline under Section 5-101 of Maryland’s Courts and Judicial Proceedings Code, and the state requires insurers to offer uninsured-motorist property damage coverage with a $250 deductible, a real fallback if the driver who hit you had no insurance at all.

How to get the real number — by yourself

This whole thing comes down to one piece of paper that out-argues the formula with actual market data.

1. Get a diminished value appraisal. What you want is a certified appraiser who works to “USPAP” — that’s just the national standard for appraisals that hold up, the same one banks trust. They’ll line up real sales of cars like yours, some with a wreck on the record and some clean, and show what the accident actually costs you. It runs a few hundred dollars, and it hands you a number the insurer has to actually deal with instead of brushing off. Everything else rides on this one step. Bring the repair invoice, before-and-after photos, your vehicle history report, and your VIN and current mileage — that lets an appraiser turn the report around in days instead of weeks. If your car was worth under about $8,000 before the wreck, or the odometer had already cleared 100,000 miles, run that math first. The appraisal fee itself can eat a meaningful share of what you’d actually recover.
2. Send it over with a short demand letter. Don’t let “demand letter” scare you — it’s a one-page note. Put the claim number, your appraised figure, the appraisal attached, and a 30-day deadline. Mail it certified, and keep it calm and factual. You’re not venting; you’re building a paper trail. Our demand letter guide has a copy-ready template if you want the exact wording.
3. Don’t fold when they push back. Odds are they’ll bounce the 17c number right back at you. Send your appraisal again and ask them, in writing, to explain how they got their figure. A formula their own regulator has walked away from doesn’t survive that question for long.
4. Turn up the heat if they drag their feet. A complaint to your state insurance department is free and tends to actually get a response. Search “[your state] department of insurance complaint” to find the online form. And small claims court is always waiting in the wings. Its dollar limit runs from about $2,500 to $25,000 depending on the state, so most diminished value claims fit under it, and you can file one yourself without a lawyer.

For most people, that’s the whole game. But I’m not going to pretend every claim is a do-it-yourself job. So let’s be straight about when to bring in help.

So… do it yourself, or call a lawyer?

For a plain diminished value claim, the honest answer is usually: you’ve got this. We’re often talking a few thousand dollars, small enough to handle yourself — and a contingency fee (the slice the lawyer keeps if you win) would eat a chunk of what you fought for. The appraisal does the heavy lifting, and everything above is meant to be run solo.

That said, I’d be doing you a disservice if I didn’t flag the cases where a lawyer’s read is genuinely worth it:

Left column? Do it yourself, and the reason is cost. A diminished value claim usually has no fee-shifting law behind it, so a lawyer works on contingency: their fee, about a third, comes straight out of your recovery. On a few-thousand-dollar claim that fee costs you more than a lawyer would add. And the work is simple enough to handle yourself — an appraisal, a demand letter, and small claims if it comes to that. No lawyer’s fee comes out of it, so you keep the full recovery.

Right column, or a foot in both? Here a lawyer barely costs you, and that flips the math. On a bigger or disputed claim they net you more than you’d get alone even after the fee, because they handle the proof and the negotiation you’d be stuck doing solo. And if the insurer acted in bad faith, many states make it pay your attorney fees and extra damages — so the lawyer can cost you nothing at all. The bigger or uglier the claim, the more that’s worth it. One paid consultation tells you which side you’re on, with no commitment past that.

Bottom line

Treat that 17c figure as the insurer’s first move, not the last word. Run your real numbers, get an appraisal if the gap is worth chasing, and send the demand. The reason this money usually goes unclaimed is almost embarrassingly simple. People just never ask. The insurer is betting you won’t either. Prove them wrong.

Ready to get the real number? Our diminished value appraisal guide covers what a certified appraisal actually costs in 2026, which appraiser credentials actually matter (USPAP is the one that counts, and the guide explains why the repair-shop certifications like ASE and I-CAR don’t), and how to use the report to get paid.