Free tool

Diminished value calculator

See exactly how an insurer's 17c formula reaches its number, then measure your car's lost value from real listings or dealer offers. The result is a range with the evidence behind it, plus a letter you can send.

A repaired car with an accident on its history report usually sells for less than the same car without one. That gap is diminished value. Insurers that pay it often use a formula commonly called 17c, which can produce a low figure by design. This page shows the formula in the open, next to a market-based measure, so you can compare the two.

This mode reproduces the formula many adjusters call "17c" so you can see how an insurer's number may have been built. It is an insurer method, not a legal standard. Pick the damage level and enter the mileage the way an adjuster would.

Pre-crash value of the car ($)Retail value just before the crash, for example from a valuation guide or the insurer's report.Damage levelThe adjuster chooses this. It is the most subjective step.Odometer miles at the crash

17c-style result

$1,200

What an insurer using this formula would likely compute

If the damage level is rated one step lower or higher

$600 to $1,800

Most this formula can ever produce

$3,000

10% of the pre-crash value

Every step

Base loss (the 10% cap): $30,000 × 0.10 = $3,000
Damage multiplier for "moderate damage to structure and panels": $3,000 × 0.50 = $1,500
Mileage multiplier for 20,000 to 39,999 miles: $1,500 × 0.80 = $1,200

Without the mileage step, the same damage rating would give $1,500. The mileage step removed $300.

The two multiplier tables
Damage level	×	Miles	×
Severe damage to the structure	1.00	0 to 19,999	1.00
Major damage to structure and panels	0.75	20,000 to 39,999	0.80
Moderate damage to structure and panels	0.50	40,000 to 59,999	0.60
Minor damage to structure and panels	0.25	60,000 to 79,999	0.40
No structural damage (panels replaced or repaired)	0.00	80,000 to 99,999	0.20
		100,000 or more	0.00

Evidence checklist

Tick what you have. Ticked items are listed as enclosures in the letter.

Final repair invoice, including supplements and any frame or structural line items
Photos of the damage before repair and of the finished repair
A vehicle history report showing the accident is now on record
Written dealer offers (with and without the accident history) on letterhead
Comparable listings saved as PDFs or screenshots with dates, VINs and mileage
An independent diminished value appraisal, if the amount justifies the fee
The claim number, the at-fault driver's insurer and the adjuster's name

For the letter (optional)

The letter uses the range from the market evidence mode. Until you enter market evidence, it asks the insurer to consider the claim and explain its method.

Your nameAt-fault driver's insurerClaim numberYour vehicleInsurer's offer so far ($, optional)Amount you will request ($)Enter market evidence first, or type an amount.

Your demand letter

[Your name]
[Your address]
[Your phone and email]

[Date]

[Insurance company]
[Adjuster name and address]

Re: Diminished value claim
Claim number: [claim number]
Your insured: [name of the at-fault driver]
My vehicle: [year, make, model, VIN]

Dear Adjuster:

Although my vehicle has been repaired, it is now worth less because it has an accident on its record. I am gathering market evidence of the loss and will send it separately. Please confirm in writing that you will consider a diminished value claim and tell me what documents you need.

Enclosed:
- [list your evidence]

I ask for a response within 30 days of the date of this letter. This letter concerns diminished value only. It does not settle, release or waive any other part of my claim.

Sincerely,

[Your name]

By Serdar Arslan, editor · Last reviewed November 3, 2026 · How we research

How the tool works

Mode 1, insurer formula (17c): takes 10% of the pre-crash value as the starting point and the ceiling, multiplies it by a damage factor (1.00 for severe structural damage down to 0.00 for no structural damage) and then by a mileage factor (1.00 under 20,000 miles down to 0.00 at 100,000 or more). Each step is printed. Because the adjuster picks the damage level, the tool also shows the result one level up and one level down.
Mode 2, market evidence: compares asking prices for matching cars with and without an accident history, or uses written trade-in offers that dealers gave for your car with and without the history. It reports the observed difference as a range, not a single number.
Letter: the demand paragraph uses the market range, names the evidence you ticked, and, if you enter the insurer's offer, asks for the formula and inputs behind it in writing.

Where 17c comes from

In State Farm v. Mabry (2001), the Supreme Court of Georgia held that the insurer's duty to pay for a loss under the policies in that case included lost value, saying that "value, not condition, is the baseline," and that the insurer had to assess diminished value along with the physical damage. The formula insurers now call 17c came out of the litigation that followed. In a 2022 decision, the federal appeals court for Georgia described it as a court-approved formula that State Farm adopted after Mabry. It is an insurer method, not a law: it is not written into a statute, and the court opinions above do not say any other insurer or state must use it.

Criticisms of the 17c formula

Supporters see a quick, consistent method. Critics, including appraisers and plaintiffs in later class actions, point to three features:

The 10% cap. The result can never exceed 10% of value, whatever the market says. In the Baker case, the plaintiffs' expert said the formula always under-assesses the loss.
The mileage reduction. Mileage already lowers the pre-crash value, and the formula reduces the result again for mileage. At 100,000 miles the result is $0, regardless of the car.
No market data. None of the steps looks at what buyers actually pay for cars like yours with an accident history. The damage level is a judgment call by the adjuster.

The courts in Baker did not decide whether the formula is fair. They refused to certify a class because the plaintiffs' sample of appraisals was too small and unrepresentative to prove the point for every policyholder. For your own claim, the practical lesson is to bring market evidence about your car.

First-party and third-party claims

A third-party claim is made against the at-fault driver and their liability insurer. In most states, the property damage you can recover from the person who caused the crash can include lost market value, though insurers often resist it. A first-party claim is made under your own policy, for example your collision coverage. Whether that pays diminished value depends on your policy wording and your state, and many policies limit the insurer to repairing or replacing the car. This page does not list state-by-state rules. For more detail, including Maryland's published guidance, see our diminished value claims guide.

Assumptions and limits

The multiplier tables are the version most commonly published. An insurer may use different labels or breakpoints, so ask for its exact inputs.
The market range uses the difference of averages and of medians, widened by one standard error and floored at $0. With few listings, it is rough.
When you enter your car's value, the market percentage is applied to it. That assumes the listings are close matches.
If you share fault for the crash, the other insurer may pay only part of the loss. See the fault and compensation estimator.
The 30-day response request in the letter is a courtesy deadline you choose, not a legal one.

Worked example (hypothetical numbers)

A car worth $30,000 before the crash has 35,000 miles and needs moderate structural and panel repair. Another driver was at fault.

17c: $30,000 × 0.10 = $3,000. × 0.50 (moderate damage) = $1,500. × 0.80 (20,000 to 39,999 miles) = $1,200.
Market: three matching clean-history listings at $29,500, $30,200 and $31,000 (average $30,233) and three accident-history listings at $26,800, $27,500 and $25,900 (average $26,733). The difference of averages is $3,500, about 11.6% of the clean price. With the spread added, the tool shows a range of roughly $2,700 to $4,100 when applied to the $30,000 value.

The owner sends the letter with the repair invoice, the history report and the saved listings, asks for about $3,500 rather than the top of the range, and asks the insurer to explain its $1,200 figure in writing. If the insurer will not move and the amount is within the limit, small claims court is one option. For a large gap, an independent appraisal or a lawyer may be worth the cost.

Frequently asked questions

›What is the 17c formula?

It is a diminished value method used by some insurers. It starts at 10% of the car's pre-crash value, multiplies that by a damage factor from 0 to 1, then by a mileage factor from 0 to 1. The name is tied to Georgia litigation that followed State Farm v. Mabry (2001). It is not a statute or a regulation, and no law we know of requires you to accept a number produced by it.

›Can I claim diminished value if the crash was my fault?

Usually not against another driver's insurer, because that claim depends on the other driver being at fault. A claim under your own policy (first-party) depends on your policy wording and your state. Many policies pay to repair the car, not for lost market value, and some exclude diminished value outright. Read your policy and ask your insurer in writing.

›Is a market-based number better than the 17c number?

It is based on different evidence. A market comparison uses prices buyers and dealers actually set for cars like yours, with and without an accident history. Its weakness is matching: if the comparable cars differ in trim, miles or condition, an adjuster may dismiss them. Good comparables or written dealer offers are usually more persuasive than a formula result alone.

›Does diminished value apply if my car was totaled?

Generally no. When a car is a total loss, the insurer pays its pre-crash value, so there is no repaired car left to lose value. Diminished value comes up when the car is repaired and kept.

›Should I pay for an independent appraisal?

It depends on the size of the gap. An appraisal costs money but gives you a written report from someone who does this for a living, which helps if you end up in small claims court. For a small difference, written dealer offers and saved listings may be enough. This tool does not replace an appraisal.