Two components with different jobs
The excess is the amount deducted from any claim settlement before the insurer pays. On most policies it is stated as a single total, and that total is the sum of a compulsory excess set by the insurer and a voluntary excess chosen by the customer at the point of purchase. They look identical on the schedule and they exist for completely different reasons.
The compulsory portion is a pricing decision. The insurer has decided it will not carry the first slice of a loss for a driver with this profile in this vehicle, and the slice tends to grow for risks it considers less predictable. The voluntary portion is a customer choosing to keep more of the small losses in exchange for a lower price.
Why any excess exists at all
Three separate forces push in the same direction here. The first is administrative: handling a claim costs money regardless of its size, and for very small losses the cost of assessing, processing and paying can approach the payment itself. Removing that whole band of claims from the system is efficient in a way that benefits everyone in the pool.
The second is moral hazard, which is the tendency for behaviour to shift once a risk has been transferred to someone else. A driver who bears none of the cost of a minor scrape has slightly less reason to avoid one. Nobody serious claims this effect is enormous, and it is easy to overstate, but it is not zero and it is priced.
The third is simple attrition. High-frequency, low-severity damage is not really an uncertain event over the life of a car; it is closer to a running cost with an irregular schedule. Insurance handles the unlikely and expensive far better than it handles the likely and cheap.
What raising the voluntary excess actually buys
The discount reflects the expected value of the claims the insurer no longer expects to pay, plus the administration it saves. Because small claims are far more common than large ones, the first increment of voluntary excess removes a substantial slice of expected cost and earns a meaningful reduction in price.
Each further increment removes less. Pushing the excess higher only excludes claims in a band that was already rare, so the extra discount tapers away while the amount you would have to find after an incident keeps climbing. That is the trade in its honest form: you are converting a small certain saving into a larger uncertain liability, and the exchange rate gets worse the further you take it.
Whether that trade suits any particular household depends on things an article cannot know. It is worth being clear that the excess falls due at the moment of the loss, which is often when several other costs arrive at once.
The excesses you did not choose and may not have noticed
Beyond the headline figure, most wordings contain additional excesses that apply only in certain circumstances. An extra amount for a driver under a stated age, or below a stated period of licence tenure, is near-universal. Separate excesses commonly attach to windscreen and glass claims, to theft, to fire, and sometimes to claims arising when the vehicle was being driven by a named driver rather than the policyholder.
These usually stack rather than replace one another. A young driver making a theft claim can find two or three additions applying to the same loss, and the total bears little resemblance to the number remembered from the quotation. The schedule lists them, generally in a table that is very easy to skim past.
How it is actually paid, and when it comes back
In practice the excess is either deducted from a cash settlement or paid directly to the repairer when you collect the vehicle. You do not send it to the insurer in advance. If another party is fully liable and their insurer accepts that, your insurer will normally pursue recovery and refund your excess once it succeeds, which can take months rather than weeks.
Products exist that reimburse an excess after a claim. They are separate contracts with their own terms and exclusions, and they do not change how the claim itself is treated: the claim still happens, still sits on your record, and is still settled net of the excess before any reimbursement arrives. Whether such a product is worth buying is a personal judgement that turns on its own wording.
