Part of our guide to What Insurance Do You Actually Need? A Plain Guide to Each Type
Two people with the same car and the same clean record can pay very different amounts. That is not a mistake or a negotiating trick — it is the rating factors doing their job. Knowing which ones you can move is worth more than any switching gimmick.
Premiums are built from where the car lives, who drives it, what it is, and how much risk you keep yourself. Location and claims history do most of the work. The two things most under your control are the deductible and shopping between insurers — because companies weight these factors differently, the same driver gets genuinely different prices.
What actually goes into the number
Where the car is parked overnight. Usually the single largest factor, and the one drivers underestimate. Rating is done by garaging location — theft rates, vandalism, accident frequency, repair costs and how litigious the area is all feed in. Moving a few miles can change a premium materially.
Your claims history. Not just at-fault accidents. Comprehensive claims count too, though usually less. Most insurers look back three to five years.
Your driving record. Moving violations, at-fault accidents, and licence suspensions. A single speeding ticket usually raises the premium at next renewal.
The vehicle. Not "expensive car costs more" — it is more specific than that. Repair cost, parts availability, theft rate for that model, and how the car performs in crash testing all feed in. Two cars at the same price can rate very differently.
Coverage choices. Liability limits, deductible, and whether you carry comprehensive and collision. This is the part you set directly.
Annual mileage. Fewer miles, less exposure.
Continuous coverage. A gap in insurance usually raises rates, sometimes sharply.
What may or may not be allowed, depending on your state
This is where it gets state-specific, and where advice from elsewhere stops applying.
Credit-based insurance score. Most states permit insurers to use it. It is derived from credit data but is not your lending credit score. California, Hawaii, Massachusetts and Michigan prohibit it for auto insurance.
Age and gender. Widely used, but several states restrict or ban gender as a rating factor.
Marital status and occupation. Permitted in many states, restricted in others.
If you want to know what applies to you, your state's department of insurance publishes it — and they are the authority, not a comparison site.
This is the most common complaint and it has a dull answer. Insurers file rate changes with state regulators based on their overall book of claims, not yours. When repair costs, parts prices and medical costs rise, rates rise for everyone in the class — a clean record protects you from a surcharge, not from a general increase. It is also why a rise is a good prompt to re-shop: your insurer's increase is not the whole market's.
The factors, roughly ranked by weight
Insurers do not publish their rating models, and the weights differ between companies and between states — which is itself the most useful fact here, because it is why the same driver gets quotes that differ by hundreds. What follows is the general ordering, not a formula.
| Weight | Factor | Can you change it? |
|---|---|---|
| Heaviest | Claims and accident history | No — it ages off over years |
| Heaviest | Where the car is kept overnight | Only by moving |
| Heavy | Age and years licensed | Only with time |
| Heavy | The specific vehicle — repair cost, theft rate, power | Yes, at purchase |
| Heavy | Coverage level and excess chosen | Yes, immediately |
| Moderate | Annual mileage | Yes, if you genuinely drive less |
| Moderate | Moving violations | No, once they exist |
| Moderate | Credit-based insurance score, where permitted | Slowly |
| Light | Occupation and marital status, where permitted | No |
| Light | Continuous cover history | Yes — never let it lapse |
The two rows worth acting on before you buy anything are the vehicle and the coverage level. Everything above them is either fixed or takes years.
The vehicle matters more than most buyers expect
Two cars of similar price can carry very different premiums. What drives the gap:
- Repair cost — aluminium panels, sensors in the bumpers, and headlight units with cameras in them are expensive to replace after minor damage
- Theft rate for that specific model
- Power-to-weight ratio
- Safety rating, which reduces injury claims
- Parts availability
The practical instruction is short: get an insurance quote on the specific car before you agree to buy it. Not a category estimate — a quote on the registration or VIN. A $40-a-month difference is $2,400 across five years, which is enough to change which car is actually the cheaper one. The car affordability calculator has a place for exactly this figure.
Why quotes differ so much between insurers
Each company files its own rating structure with the state regulator, and they genuinely disagree about risk. One weights your postcode heavily; another weights your vehicle. One considers you a good risk; another has had bad claims experience with drivers like you.
This is why shopping produces real savings rather than marginal ones, and why the same person can get quotes hundreds of dollars apart on identical cover in the same week.
It is also why loyalty is rarely rewarded. Your renewal price reflects the book you are in, not your individual behaviour — see why your car insurance went up when nothing changed.
The two levers you actually control
The deductible. Raising it lowers the premium. Whether that is a good trade is arithmetic, not opinion — see what a deductible really costs you.
Which insurer you buy from. Underrated and the highest-yield action available. Every company runs its own rating model, so the factor that one weights heavily another treats lightly. This is why price comparisons vary so much between drivers, and why "the cheapest insurer" is not a fixed answer.
Beyond those, discounts are worth asking about explicitly rather than assuming they were applied: multi-policy, multi-vehicle, safety features, defensive driving courses, low mileage, paying in full, paperless.
What does not work
Waiting for loyalty to pay off. It generally does not. In many markets long-tenure customers pay more than new ones, not less.
Assuming a comparison site sees the whole market. Several large insurers do not appear on them at all.
Cutting liability limits to save money. This is the one place the saving is a false economy. Liability is what stands between an at-fault accident and your own assets, and the difference in premium between minimum limits and substantially higher ones is usually smaller than people expect.
Not reporting a garaging change. Rating by an address you do not live at is misrepresentation, and it can void a claim at the worst possible moment.
What to do at renewal
- Get three quotes, including at least one insurer that is not on comparison sites
- Re-check the deductible against the arithmetic, not instinct
- Ask which discounts are applied, by name
- Check your mileage is accurate if you drive less than you used to
- Leave liability limits alone unless you are raising them
This is general information, not financial advice — see our disclaimer.
Frequently asked questions
What has the biggest effect on a car insurance premium?
Where you park the car overnight, your claims history, and the coverage limits and deductible you pick. Location surprises people most — the same driver and car can cost very different amounts a few miles apart.
Does my credit score affect my car insurance?
In most US states insurers may use a credit-based insurance score, which is related to but not the same as a lending credit score. California, Hawaii, Massachusetts and Michigan prohibit its use in auto rating.
Will one speeding ticket raise my premium?
Usually yes, at the next renewal, and it typically stays in the rating for three to five years depending on the insurer and state. The size of the increase varies far more than people expect between insurers.
Why did my premium rise when I had no accidents?
Insurers file rate changes with state regulators based on overall claims costs, not just yours. Rising repair and medical costs, and claims in your area, raise everyone's rates regardless of individual record.
Is it worth shopping around every year?
Yes, and it is the highest-value action available. Insurers weight the same factors differently, so the cheapest company for one driver is often mid-priced for another. The quotes are free.
Sources
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