The 17c Diminished Value Formula Explained (and Why It Underpays)

The 17c Formula Explained

The 17c formula is how most insurers calculate diminished value — and it's built to keep the number small. It caps your loss at 10% of your car's value, then shrinks it further with damage and mileage penalties. Here's exactly how it works, step by step, and why it rarely reflects what your car actually lost.

Where the 17c formula comes from

The 17c formula traces back to the Georgia class-action case State Farm v. Mabry, which required the insurer to compensate policyholders for diminished value. The "17c" name comes from a paragraph in the settlement that laid out a calculation method. Insurers across the country adopted it — not because it's accurate, but because it produces consistently low, easy-to-defend numbers.

How the 17c formula is calculated

Step 1 — Apply the 10% cap (base loss value)

Start with the vehicle's pre-accident market value and multiply by 0.10. A $30,000 car has a base loss cap of $3,000 — the most 17c will ever allow, before it starts subtracting.

Step 2 — Apply the damage multiplier

Multiply the cap by a damage-severity factor, from 1.00 (severe structural/frame damage) down to 0.00 (no structural damage). Moderate damage might be 0.50, cutting our $3,000 cap to $1,500.

Step 3 — Apply the mileage multiplier

Multiply again by a mileage factor: 1.00 at 0–19,999 miles, scaling down to 0.00 at 100,000+ miles. At 60,000 miles (roughly 0.40), our $1,500 becomes just $600 — from a $30,000 car.

Final 17c number = base loss × damage multiplier × mileage multiplier. As you can see, each step only ever reduces the figure — which is the whole point.

Why it underpays — and what to do instead

The market doesn't cap accident depreciation at 10%, and it doesn't forgive a loss just because a car has miles on it. A certified appraisal measures your actual loss from real comparable sales — which is why market-based figures routinely beat the 17c output. See the difference for yourself on our diminished value calculator, learn how to file a diminished value claim, or start with what diminished value is.

Frequently Asked Questions

What is the 17c formula?

The 17c formula is a method insurers use to calculate diminished value. It originated from the Georgia class-action case State Farm v. Mabry. It starts by capping the loss at 10% of your vehicle's pre-accident value (the 'base loss value'), then multiplies that cap down using a damage-severity modifier and a mileage modifier. The result is the insurer's diminished value offer.

How is the 17c formula calculated step by step?

First, take your vehicle's pre-accident value and multiply by 0.10 to get the 10% base loss cap. Second, apply a damage multiplier (from 1.00 for severe structural damage down to 0.00 for no structural damage) to that cap. Third, apply a mileage multiplier (from 1.00 at 0–19,999 miles down to 0.00 at 100,000+ miles). The final figure is base loss × damage multiplier × mileage multiplier.

Why does the 17c formula underpay diminished value?

Because it starts from an arbitrary 10% ceiling instead of real resale data, and then shrinks that number further with mileage and damage penalties. A higher-mileage car can see its diminished value cut to almost nothing under 17c, even when the actual market discounts it far more for having an accident history. Real buyers don't price cars with a 17c formula — they price them on comparable sales.

Do I have to accept the 17c number from my insurer?

No. The 17c figure is the insurer's method, not a legal requirement for what you're owed. You can counter it with a certified, market-based diminished value appraisal that reflects what comparable vehicles actually sell for. A documented, USPAP-compliant appraisal is far harder for an adjuster to dismiss than the capped 17c output.