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Diminished Value

The 17c Diminished Value Formula, Explained

When you raise a diminished value claim, many insurers reach for the “17c formula.” It produces a tidy-looking number — that usually lands well below what your car actually lost. Here's how it works and why.

Reviewed by the attorneys at Conduit Law·Updated June 2026
The short version
  • ✓The 17c formula caps diminished value at roughly 10% of a base value, then cuts it further.
  • ✓It reduces the number for mileage and for damage severity using fixed multipliers.
  • ✓Those assumptions are arbitrary and frequently understate a real loss.
  • ✓It's an opening offer — you can counter it with a market-based valuation.

What is the 17c formula?

The 17c formula is a widely used method for calculating diminished value. The name comes from how the approach entered common use through insurance-claim practice, and most insurers apply some version of it. The point to understand is what it does to your number — it caps it, then shrinks it.

How the 17c calculation works

The formula generally moves through three steps:

  1. Start with a base value. Usually a published market value for your vehicle.
  2. Apply a 10% cap. The formula caps the maximum diminished value at roughly 10% of that base — your loss can’t exceed this ceiling no matter the facts.
  3. Reduce for mileage and damage. Two multipliers then cut the capped figure further: one for your car’s mileage, another for the severity of the damage.
A quick example
A $30,000 car is capped at $3,000 (10%). Apply a mileage multiplier and a damage multiplier — each less than 1 — and that $3,000 can fall to $1,500, $900, or less. Meanwhile, the market may show the car actually lost far more.

Why 17c shortchanges you

The problem isn’t your car — it’s the formula’s assumptions. The 10% cap is arbitrary and isn’t tied to what your specific vehicle does in the real market. The mileage and damage multipliers compound the reduction, and together they can turn a genuine five-figure loss into a few hundred dollars. It looks objective because it’s a calculation, but every input is a choice that happens to favor the insurer.

What to do when you get a 17c offer

Treat a 17c figure as the opening offer it is. The stronger response is a market-based diminished value figure: a comparable-vehicle analysis that shows what cars like yours actually sell for, with and without an accident on record. That’s a number built from evidence rather than a capped table — and it’s what tends to move a lowball toward a fair result.

17c formula FAQ

What is the 17c formula?+
The 17c formula is a method many insurers use to calculate diminished value. It starts from a base value, applies a flat cap (commonly 10% of that value), then reduces the figure further based on mileage and the severity of damage. The result is usually a low number relative to the car's actual lost value.
Why is the 17c formula bad for claimants?+
Because its key assumptions are arbitrary. The 10% cap isn't tied to your specific vehicle's market, and the mileage and damage multipliers can shrink a real five-figure loss down to a few hundred dollars. It's a starting offer dressed up as a calculation.
Do I have to accept a 17c diminished value offer?+
No. The 17c number is the insurer's opening position, not a binding figure. You can counter it with a market-based valuation built from comparable vehicles, which typically reflects a higher, better-supported loss.
What's a better way to calculate diminished value?+
A comparable-vehicle analysis — looking at what cars like yours actually sell for, with and without an accident on record. That measures your real loss from the market instead of applying a capped formula.

Related diminished value guides

Property Damage King is a DBA of Conduit Law. This page is attorney advertising and is provided for general educational purposes only — it is not legal advice and does not create an attorney-client relationship. Insurance and claim rules vary by state and by policy; for guidance on your specific situation, talk to an attorney. Settlement examples are real past results provided for illustration and are not a prediction or guarantee of the outcome of any future claim.