# How Are Car Insurance Premiums Calculated?

Source: https://pennyandplan.com/how-are-car-insurance-premiums-calculated/
Published: 2026-08-22 | Updated: 2026-08-22 | Category: Insurance
Publisher: Penny & Plan (https://pennyandplan.com)

**Short answer:** A car insurance premium is not a figure someone picks. It is a base rate for your coverage and location, multiplied by a series of risk factors for your vehicle, your driving record, your experience and how much you drive, then adjusted down by discounts and your chosen deductible or excess. Because the factors multiply rather than add, one bad factor lifts the entire premium rather than adding a fixed penalty. Which factors an insurer is allowed to use varies by country and even by state or province, so credit history, gender and age carry very different weight in the US, the UK and Canada.

## Key takeaways
- Your premium is a base rate multiplied by risk factors, not a number somebody chose.
- The factors multiply, so one at-fault claim lifts the whole premium rather than adding a flat penalty.
- UK insurers have been banned since January 2022 from charging renewing customers more than equivalent new ones.
- Most US states allow credit-based insurance scores; Ontario does not allow credit information in auto pricing at all.

Two neighbours park identical cars on the same street. One pays roughly half what the other pays. Neither of them negotiated, neither got a special deal, and both are with reputable insurers. The gap is not luck and it is not a scam. It is arithmetic, and once you can see the arithmetic you can work out which parts of it you are able to change.

## Your premium is a calculation, not a quote

Insurers do not look at your details and decide on a number. They start with a base rate, the average expected cost of covering one policy of that type in your rating territory, then apply a chain of factors to it. The National Association of Insurance Commissioners describes this as two separate steps: underwriting, where the insurer decides whether and on what terms to cover you at all, and rating, where a price is attached based on what the insurer expects the risk to cost.

The critical detail is that those factors multiply. They are not a list of surcharges added together. A factor of 1.40 does not add a set fee, it lifts everything underneath it by 40 percent, including all the factors already applied. That is why a single event can change a premium so dramatically, and why the same event costs one driver far more than another.

## What that looks like with real numbers

Here is an illustrative build for a driver with one at-fault claim. The figures are made up to show the mechanics, not to predict your price, but the structure is how motor pricing genuinely works.

| Step | Factor | Running premium |
| --- | --- | --- |
| Base rate, territory and coverage | 1.00 | 900 |
| Vehicle group, repair cost above average | 1.15 | 1,035 |
| Age and licence experience | 1.30 | 1,346 |
| One at-fault claim in the last three years | 1.40 | 1,884 |
| Annual mileage above average | 1.08 | 2,034 |
| Multi-policy discount | 0.90 | 1,831 |
| Higher deductible chosen | 0.92 | 1,684 |

Now look at what the claim actually cost. Strip out that single 1.40 factor and the final premium falls from 1,684 to about 1,203. The claim is adding roughly 481 a year, and if it stays on the record for three years that is close to 1,450. A minor rear-end bump repaired for less than that is a claim that costs more to make than to pay for yourself, which is the calculation worth doing before you pick up the phone. It is also the reason the [deductible or excess you choose](/what-is-a-deductible-excess-in-insurance/) is a pricing decision rather than an afterthought.

Notice too that the discounts sit at the bottom of the stack. A 10 percent multi-policy discount applied to an inflated premium saves more in absolute terms than the same discount on a clean one, which is why bundling looks so attractive to drivers who already have a poor record. It is still cheaper to fix the factor above it.

## What the multipliers are actually measuring

Every factor in that chain is a proxy for claim frequency or claim severity, the two things insurers are trying to predict.

**Frequency** is how often a group like yours has a claim at all. This is where territory, mileage, driving record and licence experience do their work. Dense urban postcodes produce more low-speed collisions and more theft, so they carry a higher base rate regardless of how carefully you drive. The NAIC identifies claim frequency as the single most influential input in rating.

**Severity** is how much each claim costs when it happens. This is mostly about the vehicle: parts prices, repair complexity, whether the bumper contains sensors, and how expensive the cars it typically collides with are. Two cars with identical purchase prices can sit in very different rating groups because one has cheap panels and the other needs a recalibrated camera array after a parking scrape.

That distinction explains a lot of otherwise confusing pricing. A modest, boring car with a high-tech driver assistance package can rate worse than an older model that costs the same to buy, because assistance hardware is expensive to replace even when the crash is trivial.

## The rules are not the same in the US, UK and Canada

This is where most guides stop, and it is where the real differences are. What an insurer may legally use to price you depends entirely on where you live.

| Rating factor | United States | United Kingdom | Canada |
| --- | --- | --- | --- |
| Credit history | Allowed in most states, prohibited in a few including California, Hawaii and Massachusetts | Insurers may use credit data, subject to FCA rules and data protection law | Not permitted in Ontario auto insurance; treatment varies elsewhere |
| Gender | Allowed in most states, banned in several | Not permitted as a rating factor | Restricted or banned in some provinces |
| Who regulates the rate | State insurance departments, with filing rules varying by state | Priced freely by insurers, conduct regulated by the FCA | Provincial regulators, with rate approval in provinces such as Ontario |
| Basic cover provider | Private insurers | Private insurers | Public in British Columbia, Saskatchewan and Manitoba; hybrid in Quebec |

**United States.** Rates are regulated state by state, not federally, and the biggest divergence is credit. The FTC's report to Congress on credit-based insurance scores found that these scores do predict claims, while also finding that African-American and Hispanic consumers tend to have lower scores as a group and therefore tend to pay relatively more where scores are used. That finding is the backdrop to the state-level bans. If you live in a state where credit is used, improving your credit file is one of the few levers that quietly moves an auto premium without changing anything about your driving.

**United Kingdom.** There is no state-by-state variation, but there is a rule that does not exist in North America. Since January 2022, following the FCA's general insurance pricing practices work, insurers cannot offer a renewing home or motor customer a price higher than the equivalent new business price they would offer a new customer for the same policy. That killed the old routine of quoting a cheap first year and walking the price up on loyal customers. Shopping around still helps, because different insurers rate the same driver differently, but the specific trick of being punished for staying is gone. Separately, keeping a vehicle insured continuously is a legal requirement rather than a choice, and GOV.UK sets out the penalties for letting cover lapse on a vehicle that is not formally declared off the road.

**Canada.** The market is genuinely split. Basic coverage in British Columbia, Saskatchewan and Manitoba comes from public insurers, and Quebec runs a hybrid where bodily injury cover is public and vehicle damage is private. Elsewhere, private insurers file rates with the provincial regulator. In Ontario, FSRA oversees that process, and Ontario prohibits the use of credit information in auto insurance pricing entirely, which is a much stronger position than most US states take. If you move provinces, expect the whole basis of your price to change rather than just the number.

## Which levers actually move the number

Ranked by how much they shift the premium relative to the effort involved:

**The car itself.** Before you buy, ask what insurance group or symbol the exact trim sits in. This is the largest single input you fully control, and it is far easier to choose a cheaper car to insure than to argue a premium down afterwards.

**Not making small claims.** Run the arithmetic from the table above. If the likely surcharge over three years exceeds the repair cost, pay it yourself.

**Mileage accuracy.** Many drivers estimate their annual mileage once and never revise it downward after changing jobs or moving. Report it accurately, both because overstating costs money and because understating it can affect a claim.

**The deductible.** A genuine lever, but only up to the amount you could pay tomorrow without borrowing.

**Telematics, if you actually drive well.** Usage-based policies price on measured braking, acceleration, mileage and time of day. They reward calm, low-mileage drivers and penalise late-night or hard-braking ones, so they are worth it only if you are honestly in the first group.

**Credit, where it is used.** Irrelevant in Ontario, irrelevant in the US states that ban it, quietly significant everywhere else.

What barely moves it: haggling. Motor pricing is model-driven, so there is very little discretion for a call centre agent to hand you.

## The bottom line

A car insurance premium is a base rate multiplied up and down by factors that each stand in for how often people like you claim and how much those claims cost. Because the factors multiply, the fastest way to a lower price is removing a bad factor rather than hunting for another discount at the bottom of the stack. Check which factors your jurisdiction even permits, because a credit file that is costing you money in one country is legally irrelevant in another, and then compare at least three insurers, since each of them weights the same factors differently.

## Frequently asked questions

**Why did my premium go up when I did nothing wrong?**

Premiums move for reasons that have nothing to do with you. Insurers reprice when repair and parts costs rise, when injury claim costs in your area increase, or when their own claims experience for drivers like you worsens. Your individual factors are only half the calculation; the base rate for your territory and coverage is the other half, and that is set from group data.

**How long does an at-fault accident affect my premium?**

Typically three to six years depending on the insurer and the jurisdiction, with the largest surcharge in the first year or two and a taper after that. Because the accident factor multiplies the whole premium rather than adding a fixed amount, the total cost over that window is usually far larger than the claim payout on a small collision.

**Does raising my deductible always save money?**

It lowers the premium, but the saving is only real if you can pay the higher deductible without borrowing. Compare the annual saving against the extra you would have to find at claim time. Raising a deductible to save a modest amount each year is a poor trade if it means the excess is more than your emergency fund.

## Sources
- Auto Insurance (National Association of Insurance Commissioners): https://content.naic.org/consumer/auto-insurance.htm
- Credit-Based Insurance Scores: Impacts on Consumers of Automobile Insurance, A Report to Congress (US Federal Trade Commission): https://www.ftc.gov/reports/credit-based-insurance-scores-impacts-consumers-automobile-insurance-report-congress-federal-trade
- Vehicle insurance (GOV.UK): https://www.gov.uk/vehicle-insurance
- PS21/11: General insurance pricing practices, amendments (UK Financial Conduct Authority): https://www.fca.org.uk/publications/policy-statements/ps21-11-general-insurance-pricing-practices-amendments
- Car insurance (Financial Consumer Agency of Canada): https://www.canada.ca/en/financial-consumer-agency/services/insurance/car.html
- Auto Insurance (Financial Services Regulatory Authority of Ontario): https://www.fsrao.ca/consumers/auto-insurance