The property half is the easy half
Repairing or replacing a car is a bounded problem. There is an upper limit set by what the vehicle is worth, the cost can be estimated within days of the incident, and the file can be closed inside weeks. Insurers understand this part well, price it accurately and compete on it, because the data is plentiful and the outcomes are predictable.
That is not where the money goes. Across a motor book, the great majority of claims by number are damage claims, and a comparatively small number of injury claims consume a share of the total cost out of all proportion to how often they occur. Frequency lives in one half of the product and severity lives in the other.
Injury has a long tail and no natural ceiling
A serious injury claim compensates lost earnings over a working life, care and assistance possibly for decades, adaptations to housing and transport, and the injury itself. There is no equivalent of market value to cap it. The upper end of the distribution is very far from the middle, and a single catastrophic claim can cost more than thousands of ordinary ones together.
Liability limits vary by jurisdiction, and some legal systems require cover for personal injury without any monetary ceiling at all while others set one. What that limit is where you live has to be checked locally, but the structural point holds everywhere: the tail is what has to be funded, and everybody contributes to it.
Reserving for a claim that cannot yet be valued
When a serious injury is notified, the insurer must set aside an estimate of what it will eventually cost, years before anybody knows. That reserve is an educated guess about a medical outcome, a career that might have happened, and a care regime not yet designed, and it is revised repeatedly as evidence emerges.
Those reserves are where premiums come from. Today’s price is funding an estimate of tomorrow’s liabilities, and when the estimates prove low across the market, prices rise for everyone regardless of individual records. A great deal of the movement that looks inexplicable on a renewal notice is this, working through slowly.
The assumed rate of return moves every price at once
Where a large injury claim is settled as a lump sum, the sum is calculated on the assumption that it will be invested and drawn down over the claimant’s lifetime, using a rate set by law or convention in that jurisdiction. Lower that assumed rate and the lump sum needed to produce the same income rises sharply.
This is why an adjustment to a technical financial parameter can move motor premiums across an entire country without a single accident changing. Some systems instead use periodical payments, transferring the investment risk to the insurer, which is more accurate for the claimant and much harder for insurers to fund. Both approaches exist and both are contested.
Reinsurance carries the extreme end
No insurer retains the largest claims in full. Above a chosen level, the exposure is passed to reinsurers who specialise in the tail, and the price of that protection feeds directly into the price of the underlying policies. When reinsurers reprice, the effect arrives in consumer premiums within a year or two.
It also explains why insurers care so much about aggregation: several claims from one event, or one claim that grows steadily for a decade, threaten the arrangement rather than a single account. The whole structure exists to make an unpredictable liability survivable by spreading it across companies as well as across customers.
What this explains about your own price
It explains why cheap cars are not cheap to insure. The vehicle contributes to the damage half of the exposure, but the liability half depends on where and how it is driven and by whom, and a modest car driven badly can generate the largest claim in the book. It explains why passenger-carrying, young drivers and high-mileage use are rated hard.
And it explains why third party cover is not free. The part almost everyone regards as the throwaway component of the policy is, in cost terms, the part that actually matters. What limits apply, and how injury is compensated, differ substantially between legal systems and change over time, so the local position is what governs.
