Which Modifications Must Be Declared to Your Insurer

Whether you've added an aftermarket exhaust, dropped your suspension, or swapped in a turbocharged engine, one rule applies across the board: all modifications must be disclosed to your insurance company. Failing to report even a seemingly minor change can put your entire policy at risk.

Most major carriers — including State Farm, Geico, Progressive, Allstate, and Farmers — require a formal written modification disclosure form (often called a "Custom Parts and Equipment" or "Vehicle Modification Disclosure" form) signed and officially attached to your policy. A verbal mention over the phone, or even an email without written confirmation, is not sufficient. Carriers have continued tightening their modification underwriting policies through 2025 and into 2026, with California seeing the highest rates of claim denial and policy non-renewal for undisclosed modifications.

Here's a breakdown of the most common modification categories and how insurers view each:

State Farm requires supplemental forms for any aftermarket parts totaling over $3,000 in value, with a broad definition that covers wheels, suspension, exhaust, lighting, and interior mods. Geico routes modified vehicle applications to high-risk divisions rather than denying coverage outright — but this routing results in premium increases of 65–90% above standard rates. The burden of identifying and documenting every non-stock component falls on you — even for modifications installed by a previous owner.

Modifications must also be street-legal. Any changes that violate Federal Motor Vehicle Safety Standards (FMVSS), local emissions laws, or noise ordinances can void your coverage entirely, regardless of whether they were disclosed. Learn more about custom parts and equipment coverage and how CPE endorsements protect your aftermarket upgrades.

How Modifications Impact Your Insurance Premiums

Not all modifications hit your wallet equally. Performance upgrades trigger the steepest premium increases because they signal greater accident risk and higher repair costs. Cosmetic changes tend to have a smaller impact — but they still add up. Combined modifications compound risks and costs, often pushing you into a high-risk underwriting pool.

Overall auto insurance rates have stabilized heading into 2026, with national full-coverage averages ranging from approximately $2,124–$2,496 per year depending on the source and driver profile. However, modified vehicles sit in a different risk category entirely. The premium increases below apply on top of whatever base rate you'd otherwise pay, and are driven in part by repair costs that continue to climb well above general inflation. Understanding how car insurance premiums are calculated can help you anticipate the full cost impact before committing to a build.

Performance vs. Cosmetic Modifications

Here's what you can realistically expect when modifying your vehicle:

• Engine/Performance mods (turbos, superchargers, ECU remaps): 40–90% premium increase — Geico routes these applications to high-risk divisions at 65–90% above standard; other carriers may decline outright
• Suspension modifications (drops over 1.5 inches): ~15–40% increase on top of base rate; vehicles lowered more than 1.5 inches from factory specs may trigger automatic documentation requirements
• Body kits / structural modifications: Approximately 15–20% increase depending on the insurer and scale of the modification
• Exhaust system changes: Average increases around 15–16% for performance exhaust; legal compliance with emissions laws is essential
• Wheel and suspension combos (e.g., 22-inch rims + 2-inch drop): Compounded risk assessment; annual premiums can reach $3,000–$6,000 for daily drivers
• Cosmetic mods (custom paint, spoilers, body kits): 5–25% increase depending on the insurer and vehicle value; alloy wheels alone may add as little as 0.8–4.5%
• Minor safety upgrades (upgraded brakes, anti-theft systems, GPS immobilizers, backup cameras): May qualify for discounts with select carriers

Drivers in certain states face even steeper consequences. California has become one of the harshest markets for modified vehicle coverage, with agents reporting frequent claim denials for undisclosed modifications — particularly wheels more than 2 inches larger than stock or drops greater than 1.5 inches. Understanding what affects your car insurance rates can help you anticipate the full cost impact before committing to a build. You can also learn more about custom parts and equipment coverage to understand your options before making changes.

Aftermarket Parts Coverage vs. OEM — What's Actually Covered?

This is one of the most misunderstood areas of modified car insurance. Standard auto policies are built around OEM (Original Equipment Manufacturer) parts — the factory components your car shipped with. If you've replaced those with aftermarket upgrades, your standard policy may not cover their full value. For a deeper look at how OEM vs. aftermarket repair parts affect your coverage, see our guide on OEM parts coverage.

Actual Cash Value vs. Agreed Value Policies

For modified vehicles, agreed value policies are strongly recommended. With ACV coverage, your insurer's adjuster will reference comparable stock vehicles, completely ignoring the value of your aftermarket parts. In a total loss scenario, you could receive a payout thousands of dollars short of your actual investment. To learn more about how depreciation is applied in standard claims, see our guide on depreciation in car insurance claims.

Agreed value policies allow you to document and negotiate the inclusion of all modifications upfront — ensuring a full payout (minus your deductible) with no depreciation disputes. Many specialty insurers offer Custom Parts and Equipment (CPE) endorsements that extend coverage to aftermarket modifications. CPE endorsements typically carry a deductible of $250–$1,000, with annual premiums ranging from approximately $80–$250 depending on the coverage level and risk profile. Coverage limits vary widely by insurer:

• Progressive: Up to $5,000 in CPE coverage for cars (automatically up to $3,000 for motorcycles; purchasable up to $30,000)
• Elephant Insurance: Automatic $1,000; purchasable up to $20,000
• Allstate: Flexible customizable limits; approximately $102/year add-on
• Esurance: Up to $4,000 in CPE coverage
• Hagerty: Guaranteed Value® (agreed value) with full modification documentation and no depreciation

If your vehicle is imported or features non-standard components, review our guide on insurance for imported vehicles to understand how grey-market and JDM cars are handled. For classic and collector builds, classic car insurance provides a deeper look at agreed value coverage requirements.

Best Insurance Companies for Modified Cars

Not every insurer is equipped to handle heavily modified vehicles. Here are the top options available in 2026, ranging from major carriers with CPE add-ons to specialty insurers built specifically for enthusiasts.

Specialty / Collector Insurers

Major Carriers with Modification Coverage

Not sure whether your current policy is working for your vehicle? Review our guide on car insurance endorsements to understand which add-ons provide the most value for your situation. If you own a high-value build, luxury and exotic car insurance covers specialized coverage for premium vehicles in detail. You can also check what to look for in car insurance to make sure you're evaluating policies the right way.

Consequences of Not Declaring Modifications

The risk of staying silent about your modifications is far greater than the cost of a higher premium. Major carriers are actively denying claims based on undisclosed modifications and systematically non-renewing policies when aftermarket parts are discovered during inspections. Here's what can happen when you file a claim on a policy with undisclosed modifications:

1. Claim denial — Your insurer can refuse to pay for damages related to the undisclosed modification, even if the accident was not your fault. Aftermarket wheels, suspension changes, exhaust, or ECU tunes are easily spotted during claim inspections — and police reports noting aftermarket parts can trigger additional scrutiny.
2. Full policy voidance — The entire policy may be retroactively voided on the grounds of material misrepresentation, leaving you personally liable for all costs
3. Fraud classification — Non-disclosure can be treated as insurance fraud, potentially barring future coverage or leading to legal consequences
4. Out-of-pocket expenses — You'll be responsible for vehicle repairs, medical bills, and third-party damages with zero insurance support
5. Permanent insurance record impact — A voided policy must be disclosed on future applications, often resulting in higher premiums or flat-out coverage refusals

This applies even if you didn't install the modifications yourself. If you purchased a pre-modified vehicle, you're still responsible for declaring every non-stock component. Understand how car insurance claims affect your rates before filing — and why a denied claim can be far more expensive in the long run. If your vehicle has a salvage or rebuilt title, insurers will scrutinize it even further — making full disclosure even more critical.

Frequently Asked Questions

Do all car modifications need to be reported to insurance?

Yes — virtually any change from the manufacturer's original specifications should be disclosed to your insurer. This includes performance upgrades, cosmetic changes (such as custom paint or body kits), interior modifications (audio systems, seat replacements), and structural alterations. Even modifications installed by a previous owner must be reported, as the burden of disclosure falls on the current policyholder. Modifications must also be street-legal and comply with FMVSS and local emissions or noise regulations — illegal modifications void coverage regardless of disclosure.

How much does modified car insurance cost compared to standard insurance?

The cost increase depends heavily on the type and extent of modifications. Performance modifications like turbos, engine swaps, and ECU tunes can raise premiums by 40–90% — with Geico routing high-performance applications to specialty divisions at 65–90% above standard rates. Suspension modifications typically add 15–40% above your base rate, while body kits and exhaust changes fall in the 15–20% range. For heavily modified daily drivers with combined upgrades, annual premiums can reach $3,000–$6,000, especially when multiple modifications compound the risk assessment.

What is the best insurance for heavily modified cars?

For heavily modified vehicles, specialty insurers like Hagerty, Grundy, and American Collectors Insurance offer agreed value policies that fully account for your modifications. Among major carriers, Elephant Insurance stands out with CPE coverage purchasable up to $20,000 — the highest standard limit available. Progressive and Allstate are solid options for moderately modified vehicles, with CPE endorsements up to $5,000 and flexible customizable limits, respectively. Drivers with extreme builds who are denied by private carriers may end up in state assigned risk pools at 2–3x standard rates.

What is the difference between agreed value and actual cash value for modified cars?

An agreed value policy locks in a pre-negotiated payout amount that you and your insurer agree on at policy inception — fully accounting for documented modifications with no depreciation applied at claim time. An actual cash value (ACV) policy pays out the depreciated market value of the vehicle using stock vehicle databases that don't account for aftermarket upgrades, which often results in a significantly lower payout on total loss. For any vehicle with meaningful modification investment, agreed value coverage is the clear choice — specialty insurers like Hagerty and Grundy make the process straightforward with thorough documentation reviews.

Can my insurance be voided if I don't declare a modification?

Yes. If you file a claim and your insurer discovers undisclosed modifications, they can void your policy retroactively on the grounds of material misrepresentation. This means your current claim will be denied and all past coverage is nullified — leaving you fully responsible for vehicle repairs, medical bills, and legal costs. You'll also be required to disclose the voided policy on any future insurance applications, which can make obtaining affordable coverage very difficult going forward. Non-disclosure can even be classified as fraud by some carriers, with potential legal implications beyond the claim denial itself.