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Diminished Value (17c) Calculator

Estimate what your car's resale value dropped after an accident, using the industry-standard 17c formula — the same starting point insurers and independent appraisers use.

Use a KBB, Edmunds, or NADA private-party value from just before the accident.
Base this on the body shop or adjuster damage report, not how it feels to drive.

Got your number? Put it in writing.

Generate a diminished value demand letter
Not legal, financial, or insurance advice. This tool gives a general, educational estimate only. Insurance laws, deadlines, and formulas vary by state, by policy, and by insurer, and they change over time. Verify anything important with your insurance policy, your state department of insurance, or a licensed attorney before relying on it. Some states restrict or prohibit first-party diminished value claims against your own insurer — check your state before filing.

How the 17c diminished value formula works

After a repair, a car carries an accident history that most buyers and appraisal guides discount, even when the repair is invisible. Diminished value is the dollar difference between what your car would have sold for with a clean history and what it’s worth now, with an accident on record.

The 17c formula, from the 2001 Georgia case Mabry v. State Farm, is the most commonly referenced starting point: it caps the base loss at 10% of the vehicle’s value, then reduces that by a damage-severity factor and a mileage factor. Insurers frequently use it (or a close variant) as their opening number.

How to strengthen a diminished value claim

  • Get a repair invoice that clearly documents the extent of the damage.
  • Consider an independent appraisal if the 17c number feels low relative to comparable vehicle listings.
  • Check whether your state allows first-party diminished value claims before filing against your own insurer.

Frequently asked questions

What is the 17c formula?

The 17c formula comes from Mabry v. State Farm (Georgia, 2001) and estimates diminished value as 10% of the vehicle's value, adjusted down by a damage-severity multiplier and a mileage multiplier. It's widely used by insurers as a starting baseline.

Is the 17c number the most I can claim?

No. It is a conservative baseline. An independent appraisal that looks at actual comparable sales of similar vehicles with and without accident history often supports a higher number, especially on newer or low-mileage vehicles.

Can I claim diminished value from my own insurance company?

It depends on your state and your policy. Some states allow first-party diminished value claims, others only allow you to claim it from the at-fault driver's insurer (a third-party claim), and a few restrict it entirely.