The 17c Formula Explained (and Why It Undervalues Your Car)

If you ask an insurance adjuster how they got their diminished value offer, there is a good chance the answer is "17c." It sounds official, almost like a section of the law. It is not a law, though, and it was not built from used car sales data. Once you see how the formula works, it becomes easy to understand why its numbers come out so low, and how to push back.

This guide walks through where 17c came from, how each step works, a set of worked examples, and a practical plan for responding to a 17c offer.

Where the 17c formula came from

In 2001 the Supreme Court of Georgia decided State Farm Mutual Automobile Insurance Co. v. Mabry. The question was whether insurers had to consider diminished value when paying claims under their own policies. The court said they did. In the class action process that followed, a formula for estimating diminished value was described in paragraph 17(c) of a court document. That paragraph gave the formula its name.

Insurers found the formula practical. It is quick, it needs only a few inputs, and it produces consistent numbers across thousands of claims. Over time it spread well beyond Georgia and became a common opening method across the industry.

That origin matters. The formula was a way to process claims efficiently, not a careful study of what an accident history does to used car prices. Knowing that gives you a reason to question its results.

The 17c formula, step by step

Diminished value = market value x 10% x damage multiplier x mileage multiplier

Step 1: Market value

The car's value right before the accident. Insurers often use J.D. Power (formerly NADA) values. Check that they used the right trim, options and condition. A wrong trim alone can shift the base by thousands of dollars.

Step 2: The 10% cap

Take 10% of the market value. This is called the base loss, and it is the most 17c will ever pay. On a $40,000 car, the ceiling is $4,000, no matter how serious the damage was.

Step 3: Damage multiplier

Damage	Multiplier	What it usually means
Severe structural damage	1.00	Frame or unibody bent, major structural parts replaced
Major structural and panel damage	0.75	Structural repair plus several panels
Moderate structural and panel damage	0.50	Some structural work and a few panels
Minor structural and panel damage	0.25	Light structural work, mostly panels
No structural damage	0.00	Cosmetic only: bumper covers, paint, trim

Step 4: Mileage multiplier

Miles	Multiplier
0 to 19,999	1.0
20,000 to 39,999	0.8
40,000 to 59,999	0.6
60,000 to 79,999	0.4
80,000 to 99,999	0.2
100,000 or more	0

Worked examples

Example 1: a $30,000 sedan

Moderate structural damage, 35,000 miles:

• $30,000 x 10% = $3,000
• $3,000 x 0.50 = $1,500
• $1,500 x 0.80 = $1,200

Example 2: a $55,000 SUV

Major structural and panel damage, 12,000 miles:

• $55,000 x 10% = $5,500
• $5,500 x 0.75 = $4,125
• $4,125 x 1.0 = $4,125

Example 3: a $24,000 pickup

Severe structural damage, 104,000 miles:

• $24,000 x 10% = $2,400
• $2,400 x 1.00 = $2,400
• $2,400 x 0 = $0

That third example is the one that surprises people. A truck with a bent frame, still worth $24,000, gets nothing under 17c because of the odometer. Try your own numbers in the diminished value calculator.

Three reasons 17c undervalues your car

1. The 10% cap is arbitrary

Nothing in the formula looks at real sales. For newer or higher end vehicles with structural repairs, dealers often knock off more than 10% of the value when they see the accident on a history report. Some buyers will not consider a car with structural damage at all, which shrinks the pool of buyers and pushes the price down further.

2. Damage multipliers cut deep

Moderate structural damage, which is a serious repair, already cuts the base loss in half before mileage is even considered. Cosmetic damage gets zero, even though a history report often does not say how minor the damage was. A buyer who sees "accident reported" does not know it was just a bumper.

3. Mileage wipes it out

Every 20,000 miles removes a large share, and at 100,000 miles the result is zero. Plenty of trucks and SUVs with more than 100,000 miles still sell for tens of thousands of dollars, and an accident record still lowers that price. The formula treats a well kept 101,000 mile truck the same as a worn out one.

When 17c is close to fair

To be fair to the formula, it is not always far off. For an older, high mileage car with light damage, 17c may be close to what buyers would actually knock off. It is least fair for newer cars, low mileage cars, valuable models and serious structural repairs. Unfortunately, those are exactly the cases with the most money at stake.

Your car	How 17c usually compares with the real loss
Older, high mileage, cosmetic damage	Often close
Mid age, average miles, moderate damage	Often low
Newer, low miles, structural damage	Often far too low
Luxury or specialty model	Often far too low

How to push back on a 17c offer

• Ask for the math in writing. Get the market value, damage multiplier and mileage multiplier they used. Mistakes are common, especially in the damage category.
• Check the damage category against your repair invoice. Frame, unibody, pillar or airbag work is structural. If they called it minor, ask why.
• Check the market value against KBB, Edmunds and J.D. Power for your exact trim and options.
• Show real market evidence: dealer trade-in quotes that mention the accident, or listings of comparable cars with and without accident history.
• Consider an independent appraisal for a newer or valuable car. It turns your argument into a professional report.
• Put it in writing with a demand letter, and keep copies of everything.

For the full claim process from start to finish, read What Is Diminished Value and How to Claim It. If your car is leased or financed, also read diminished value after a lease or loan.

The bottom line

The 17c formula is a starting point that insurers chose because it is simple and predictable. It is not the law, it is not based on sales data, and it tends to favor the insurer. Use it to understand the opening offer, then use real evidence to argue for the loss your car actually took.

How to check an insurer's 17c worksheet

Some insurers send a short worksheet with their offer. Others only give a number. Either way, ask for these five items and check each one:

Item	What to check
Vehicle description	Correct year, make, model, trim and options
Market value source	Which guide, which date, which condition rating
Damage category	Matches the repair invoice, especially any structural work
Mileage	The odometer reading on the day of the crash, not today
Math	10% of value, then each multiplier, in that order

Errors are more common than you might expect. A base trim entered instead of a higher trim, or "minor" damage entered for a repair that included frame straightening, can cut the offer in half.

17c vs an independent appraisal

	17c formula	Independent appraisal
Based on	A fixed formula	Market data for your car
Cost to you	Free	A fee to the appraiser
Caps the loss	Yes, at 10%	No
Handles high mileage	Drops to zero at 100,000 miles	Looks at real buyers
Best for	Older, lower value cars	Newer, valuable or heavily damaged cars

Frequently asked questions

Is the 17c formula the law?

No. It is a method many insurers use as a starting point. You can present other evidence, like an independent appraisal or comparable sales.

Why does 17c give zero for my car?

Either the damage was classified as cosmetic, or the car has 100,000 miles or more. Both multipliers drop to zero at those points.

Do all insurers use 17c?

Not all, but it is widely used as an opening method, especially for third-party claims. Some insurers use their own variations.

Can I negotiate a 17c offer?

Yes. Check each input, correct any mistakes, and send evidence that the real loss is higher. Many offers move once you do.

What is the maximum diminished value under 17c?

10% of the car’s pre-accident value, and only when the damage is severe and the car has fewer than 20,000 miles.

Where did the name 17c come from?

It comes from paragraph 17(c) of a court document in the Georgia litigation that followed the 2001 State Farm v. Mabry decision.