The 17c Diminished Value Formula, Explained

What Is the 17c Formula?

The 17c formula is a widely used method for calculating diminished value. The name comes from an old Georgia case appendix, 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. It looks objective because it is a calculation, but every input is a choice, and the choices tend to favor the insurer rather than your specific car.

The Quick Takeaways

• It caps your loss. The formula limits diminished value to roughly 10% of a base value, no matter the facts.
• Then it cuts further. Mileage and damage-severity multipliers reduce that capped figure again.
• Its assumptions are arbitrary. The 10% cap is not tied to what your vehicle does in the real market.
• It is an opening offer. A 17c number is a starting position you can counter with a market-based valuation.

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 cannot exceed this ceiling no matter the facts of the crash.
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 shows how fast the number falls: 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 drop to $1,500, $900, or less. Meanwhile, the market may show the car actually lost far more.

Why 17c Shortchanges You

The problem is not your car — it is the formula's assumptions. The 10% cap is arbitrary and is not 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. The math feels neutral, but it is built on inputs that consistently produce a small result. That is why a number that looks precise can still be far below what comparable sales would support.

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 is a number built from evidence rather than a capped table — and it is what tends to move a low first offer toward a fair result. If you want to understand the underlying loss first, our plain-English guide to diminished value explains where the gap comes from, and our guide to filing a claim walks through how to put the demand together.