Diminished Value Guide
The 17c Formula: How It Works + Free Calculator
The 17c formula is how most insurers calculate diminished value, and it's built to keep the number small. It caps your loss at 10% of your car's value, then shrinks it further with damage and mileage multipliers. Run your numbers below to see the 17c figure next to your car's likely real loss, then read how the formula works and how to challenge it.
17c calculator: the insurer's number vs. your real loss
Diminished Value Estimator
See what the insurance company's formula says your claim is worth.
Disclaimer: This calculator provides a rough estimate based on the insurance industry's standard 17c formula. It is not a certified appraisal and does not guarantee settlement amounts. Only a licensed auto appraiser can determine actual diminished value through a certified market analysis.
Where the 17c formula comes from
The formula traces back to the 2001 Georgia Supreme Court case State Farm Mut. Auto. Ins. Co. v. Mabry, which required insurers to pay diminished value to their own policyholders. State Farm responded with a standardized calculation, named after a paragraph of the court filings in that case, to settle those claims at scale. It was never validated against actual used-car sales data. Insurers across the country adopted versions of it because it's cheap, not because it's accurate.
Even in Georgia, where it started, the state's Department of Insurance directed carriers in December 2008 that no fixed formula, including 17c, may be the sole measure of diminished value. See our Georgia diminished value law guide for how that plays out in a claim.
How the 17c formula is calculated
Step 1 — Apply the 10% cap (base loss value)
Start with the vehicle's pre-accident market value and multiply by 0.10. A $30,000 car has a base loss cap of $3,000, the most 17c will ever allow before it starts subtracting.
Step 2 — Apply the damage multiplier
| Severe structural damage | 1.00 |
| Major damage to structure and panels | 0.75 |
| Moderate damage to structure and panels | 0.50 |
| Minor damage to structure and panels | 0.25 |
| No structural damage (superficial only) | 0.00 |
Moderate damage (0.50) cuts our $3,000 cap to $1,500. The adjuster chooses the category, and there are no strict definitions, so they often pick the lowest one they can justify.
Step 3 — Apply the mileage multiplier
| 0 – 19,999 miles | 1.00 |
| 20,000 – 39,999 miles | 0.80 |
| 40,000 – 59,999 miles | 0.60 |
| 60,000 – 79,999 miles | 0.40 |
| 80,000 – 99,999 miles | 0.20 |
| 100,000+ miles | 0.00 |
At 60,000 miles (0.40), our $1,500 becomes just $600, from a $30,000 car.
17c figure = vehicle value × 0.10 × damage multiplier × mileage multiplier. Every step only ever reduces the number, which is the whole point.
Why the 17c formula underpays
- The 10% cap has no basis in real data. Newer vehicles with structural damage frequently lose well over 10% of their value. The formula treats every car the same.
- The damage category is subjective. "Moderate" versus "major" is a judgment call, made by someone working for the insurer.
- High-mileage cars get zeroed out. Over 100,000 miles, 17c returns $0, even though a well-kept high-mileage car still sells for real money and an accident still lowers that price.
- It never looks at comparable sales. A proper appraisal compares your car to similar vehicles sold with and without accident history. 17c applies generic multipliers instead.
A certified appraisal starts from your car's actual local market, which is why market-based appraisals routinely beat the 17c output.
How to challenge a 17c offer
- 1
Ask for the calculation in writing
Request the full 17c breakdown from the adjuster: the pre-accident value they used, the damage multiplier, and the mileage multiplier. You're entitled to see how they reached their number, and the damage category is often where the lowball hides.
- 2
Get a certified appraisal
An independent, market-based appraisal documents what your car actually lost using comparable sales. That report becomes your counter-offer.
- 3
Send a written demand
Send the insurer a formal demand with the appraisal attached. Many claims settle at this stage.
- 4
Escalate if they won't move
Depending on your state, you can file a complaint with the state insurance department, use your policy's appraisal process where it applies, or take a smaller claim to small-claims court.
Use our free demand letter template for step 3, and see the full diminished value claim guide or how to file a claim for the whole process.
17c Formula FAQ
What is the 17c formula?
The 17c formula is a method insurers use to calculate diminished value. It came out of the 2001 Georgia case State Farm Mut. Auto. Ins. Co. v. Mabry. It caps the loss at 10% of your vehicle's pre-accident value, then multiplies that cap down using a damage-severity multiplier and a mileage multiplier. The result is the insurer's diminished value offer.
How is the 17c formula calculated step by step?
Multiply your vehicle's pre-accident value by 0.10 to get the base loss. Multiply that by the damage multiplier (1.00 for severe structural damage down to 0.00 for no structural damage). Then multiply by the mileage multiplier (1.00 under 20,000 miles down to 0.00 at 100,000+ miles). Vehicle value × 0.10 × damage × mileage = the 17c figure.
Is the 17c formula required by law?
No. No state requires insurers to use 17c. It's an internal method, not a legal standard for what you're owed. You can dispute the result and present a certified appraisal as evidence of your real loss.
What is the 17c formula used for in Georgia?
Georgia is where 17c started: State Farm used it to settle diminished value claims after the Mabry decision required Georgia insurers to pay diminished value on first-party claims. In December 2008, the Georgia Department of Insurance directed carriers that no fixed formula, including 17c, may be the sole measure of diminished value. Insurers still lead with it anyway.
Why does the 17c formula underpay diminished value?
It starts from an arbitrary 10% ceiling instead of real resale data, lets the adjuster pick the damage category, and zeroes out any car over 100,000 miles. Real buyers don't price cars with a formula; they price them on comparable sales, which is why a market-based appraisal usually comes in higher.
Why do insurers still use the 17c formula?
Because it's fast to apply at scale and reliably produces low numbers, and most people accept the first offer without pushing back.
What if the insurer refuses to pay diminished value at all?
Some insurers deny the claim outright. Your options include a written demand backed by a certified appraisal, a complaint to your state insurance department, or a claim against the at-fault driver directly, often in small-claims court for smaller amounts.
Can I get diminished value from my own insurance?
Usually not. Most states only require the at-fault driver's insurer to pay diminished value. Georgia is the main exception: under Mabry, insurers there must also evaluate diminished value on first-party claims.
Beat the 17c lowball.
Get a certified, market-based appraisal that reflects your car's real loss. Get paid or you don't pay.