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 is not enough.

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

State Farm, for example, 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. The burden of identifying and documenting every non-stock component falls on you, even for modifications installed by a previous owner.

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.

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
• Suspension modifications (drops over 1.5 inches): 35–40% increase on top of base rate
• 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
• Minor safety upgrades (upgraded brakes, anti-theft systems): May qualify for discounts with some carriers

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.

Actual Cash Value vs. Agreed Value Policies

For modified vehicles, agreed value policies are strongly recommended. With ACV coverage, your insurer's adjuster will likely reference comparable stock vehicles, completely ignoring the value of your aftermarket parts. In a total loss scenario, you could walk away thousands of dollars short.

Many specialty insurers offer Custom Parts and Equipment (CPE) endorsements that extend coverage to aftermarket modifications. Coverage limits vary widely:

• Progressive: Up to $5,000 in CPE coverage
• Elephant Insurance: Up to $20,000 in custom parts coverage
• Hagerty: Agreed value with full modification documentation

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

Consequences of Not Declaring Modifications

The risk of staying silent about your modifications is far greater than the cost of a higher premium. 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
2. Full policy voidance — The entire policy may be retroactively voided, leaving you personally liable for all costs
3. Out-of-pocket expenses — You'll be responsible for vehicle repairs, medical bills, and third-party damages
4. 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.

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.

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%. Suspension modifications typically add 35–40%. Cosmetic changes tend to have a smaller impact — usually 5–25%. For heavily modified daily drivers, annual premiums can reach $3,000–$6,000 with some carriers.

What is the best insurance for heavily modified cars?

For heavily modified vehicles, specialty insurers like Hagerty and Grundy offer agreed value policies that fully account for your modifications. Among major carriers, Elephant Insurance stands out with CPE coverage up to $20,000. Progressive and Allstate are solid options for moderately modified vehicles, with CPE endorsements up to $5,000 and flexible limits, respectively.

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 the start of the policy, fully accounting for documented modifications. An actual cash value (ACV) policy pays out the depreciated market value of the vehicle at the time of the claim, typically calculated using stock vehicle databases that don't account for aftermarket upgrades — which often results in a significantly lower payout.

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 not only will your current claim be denied, but you'll also lose all past coverage — and you'll be required to disclose the voided policy on any future insurance applications, which can make obtaining affordable coverage very difficult.