Insurance companies look at modifications as extra risk. When you change your car from its factory settings, several things happen that make insurers nervous:
Higher repair costs: Modified parts are usually more expensive to fix or replace than standard ones. Custom bodywork or upgraded components need specialist work, which costs more.
Increased value: Modifications often make your car worth more money. If your car is written off or stolen, the insurer has to pay out more to replace it.
Performance changes: Modifications like turbochargers or engine upgrades can make your car faster. Insurers worry this increases the chance of accidents.
Theft risk: Modified cars can be more attractive to thieves, especially if they have expensive upgrades or eye-catching custom features.
The increase varies depending on what you've changed. According to insurance experts, you can expect modified car insurance to cost anywhere between 10% and 100% more than a standard policy. For heavily modified vehicles, premiums can be even higher than that.
Performance modifications – like engine upgrades, exhaust changes, or brake improvements – typically cause the biggest price increases. Visual changes like paint jobs or tinted windows may cost less to add to your policy, but you'll still see an increase.
Not all modifications push your premium up. Some can actually bring it down:
Security upgrades: Adding a better alarm, immobiliser, or tracking device can reduce your premium because your car is less likely to be stolen.
Safety features: Parking sensors can lower costs because you're less likely to have minor accidents.
Engine downgrades: Swapping to a less powerful engine might reduce your premium.
Even if you think a modification is small, you must tell your insurance company about any changes. If you don't declare them and need to make a claim, your insurer could refuse to pay out and your policy could be invalid. This applies whether you modify the car yourself or buy one that's already been modified.
Because different insurers treat modifications differently, it's essential to shop around. Use the comparison tool to get quotes from multiple insurers – some specialise in modified cars and offer better rates than others. Taking a few minutes to compare could save you a significant amount on your premium.
Whether you're planning a simple cosmetic change or a major performance upgrade, understanding how it affects your insurance helps you budget properly and stay fully protected on the road.
Sources
Howden Insurance - How much is modified car insurance?
https://www.howdeninsurance.co.uk/personal/motor/specialist-motor/modified-car-insurance/guides/how-much-is-modified-car-insurance/
Which? - Modified car insurance explained (January 2025)
https://www.which.co.uk/money/insurance/car-insurance/modified-car-insurance-aXxO93e1FRWo
NerdWallet UK - Modified Car Insurance (August 2025)
https://www.nerdwallet.com/uk/insurance/car-insurance/modified-car-insurance/
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