How to Calculate Diminished Value: The 17c Formula Explained

Consumer money protection · ~5 min read · Updated July 2026

After an accident, your car is worth less on the resale market — even after a flawless repair — because the collision now sits on its vehicle-history report forever. Putting a dollar figure on that loss is what "calculating diminished value" means, and the most common method is the 17c formula. Here's exactly how it works, step by step, with a worked example you can follow.

In a hurry? The Diminished Value Calculator runs this same math for you instantly.

The 17c formula in four steps

Find your pre-accident market value. Look up what your car was worth before the crash on Kelley Blue Book or NADA, matching the exact trim, options, and mileage. Everything else builds on this number.
Apply the 10% cap. Multiply that value by 10% (0.10). The 17c formula assumes diminished value can't exceed 10% of the car's worth, so this is your ceiling. A $30,000 car → a $3,000 base.
Apply the damage-severity factor. Multiply by a factor between 1.00 (severe structural damage) and 0.00 (no meaningful damage) — see the table below.
Apply the mileage factor. Multiply by a mileage factor that shrinks as the odometer climbs, because higher-mileage cars lose proportionally less resale value from an accident.

Written as one line: Diminished Value = (Market Value × 0.10) × Damage Factor × Mileage Factor.

The 17c factors

Damage severity factor:

Damage	Factor
Severe — structural / frame damage	1.00
Major — panels replaced, significant repair	0.75
Moderate — multiple panels, moderate repair	0.50
Minor — dents, scratches, one panel	0.25
Very minor — no meaningful repair	0.00

Mileage factor:

Mileage	Factor
Under 20,000	1.00
20,000 – 39,999	0.80
40,000 – 59,999	0.60
60,000 – 79,999	0.40
80,000 – 99,999	0.20
100,000+	0.00

A worked example

Say you have a $30,000 car with major damage (factor 0.75) and 35,000 miles (factor 0.80):

Pre-accident market value$30,000

× 10% cap$3,000

× Damage factor (major)× 0.75 → $2,250

× Mileage factor (35,000 mi)× 0.80

Estimated diminished value$1,800

Important: the 17c formula is conservative by design — it was originally an insurer's methodology, and independent appraisers often argue it understates real losses, especially on newer or in-demand vehicles. Treat the result as your negotiating floor, not a ceiling. A professional appraisal frequently comes in higher and isn't bound by the 10% cap.

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Now what?

A number on its own doesn't get you paid — you have to claim it. Once you have your 17c figure, the next step is filing the claim with the right insurer and countering the inevitable lowball offer. Our full guide walks through exactly how: How to File a Diminished Value Claim (and Beat the Lowball Offer).

Disclaimer: This explanation is educational and uses the industry-standard 17c formula. It is not an appraisal or legal advice, and actual diminished value depends on your vehicle, local market, and state law. For a binding figure, consult a licensed appraiser.