Voluntary Excess: How to Choose the Level That Pays Off

Your excess is the amount you pay toward any claim before the insurer pays the rest, and on UK policies it comes in two parts. The compulsory excess is set by the insurer based on your risk profile - your age, licence history, car group, postcode - and cannot be changed. The voluntary excess is the part you choose when you buy the policy, and it is the lever this article is about.

The two add together. With a £150 compulsory excess and a £250 voluntary excess, a £2,000 repair bill costs you £400 and the insurer £1,600. Three details matter for the maths later:

• It applies per claim, not per year. Two fault claims in one year means paying the excess twice.
• It bites on fault and unrecovered claims. If another driver is clearly at fault, their insurer normally ends up covering your loss and your excess is recovered or waived. The excess decision is really about claims where you carry the cost.
• Windscreen claims usually sit outside it. Most UK motor policies apply a separate, smaller glass excess, so do not let chip repairs drive your main excess choice.

Car insurance itself is a legal requirement (the government's vehicle insurance rules set the minimum), but every pound of excess above the compulsory level is a choice. Home insurance works the same way, with the wrinkle that some perils - escape of water is the classic - often carry their own higher compulsory excess.

Raising your excess is selling a slice of insurance back to the insurer. The only question is whether they are paying you a fair price for it. Two numbers decide that:

• S - the annual premium saving for raising the excess by some amount
• p - your honest annual probability of making a fault claim

Raising the excess by ΔE costs you an expected p × ΔE per year (the chance of a claim times the extra amount you would pay in that claim). So the deal is worth taking when:

S > p × ΔE

Rearranged, each step up the excess ladder has a break-even claim probability p* = S ÷ ΔE. If your real claim frequency is below p*, the step is positive expected value. If you claim more often than p*, keep the lower excess.

There is a structural reason the maths so often favours the higher excess: premiums are not pure claim costs. As we cover in how insurance companies use probability, every premium carries a loading for expenses, reinsurance and profit on top of expected claims. When you self-insure a £250 slice of risk you can comfortably afford, you keep that loading. It is the same arithmetic that makes extended warranties a poor deal for most buyers.

Here is an illustrative quote ladder for one driver, one insurer, identical cover - only the voluntary excess changes. The numbers are invented for the example, but the shape (each step saves less than the last) is exactly what real quote ladders look like:

Suppose this driver's honest record is one fault claim every eight years - an annual claim probability of about 12.5%.

Step one, £0 to £250: the break-even probability is £55 ÷ £250 = 22% a year, or a claim every four and a half years. Our driver claims far less often than that, so the step is worth an expected £55 - (0.125 × £250) = +£23.75 a year. Take it.

Step two, £250 to £500: the break-even drops to £29 ÷ £250 = 11.6% a year. Our driver's 12.5% now sits just above it: the step costs an expected £31.25 against a £29 saving, so it is -£2.25 a year. Decline it.

Same driver, same logic, opposite answers on the two steps - which is why the blanket advice you see everywhere ("raise your excess to save money") is only half right. Each step has to justify itself, and the diminishing savings mean there is usually a level where the ladder stops paying. Your own quote ladder and your own claim history are the real inputs: rerun the two divisions with those and the answer falls out.

Expected value is the right framework, but three situations override a +EV step up the ladder:

• You could not pay the excess tomorrow. An excess you would need to borrow to cover is not self-insurance, it is a trap. The repair does not start until the excess is paid, and a policy that fails you at the exact moment you need it has negative value however cheap it was. Cap your excess at what your emergency fund can absorb without drama.
• Your claim frequency is genuinely high. Multiple young drivers on the policy, theft-prone street parking, a flood-adjacent postcode on home cover: if your honest p is high, the break-even maths flips and the lower excess is the +EV choice. The formula does not care which direction it points.
• You would be tempted to game the quote. Setting a £1,000 excess you have no intention of ever paying, purely to see a lower headline premium, is self-deception with a deferred invoice.

One caveat cuts the other way: because the excess applies per claim, a year with two fault claims doubles the pain. If that risk is material for your household, weight p upward rather than using a single-claim frequency.

If the maths so often favours a higher excess, why do zero-excess policies and excess-waiver add-ons sell so well? Because a certain £55 saving against an uncertain £250 cost feels like a bad trade. Losses loom roughly twice as large as equivalent gains in human judgement - that is loss aversion - and insurers price that feeling, not just the risk. Paying a reliable premium to avoid an affordable, uncertain loss is negative expected value by construction; the product exists because the discomfort is real even when the arithmetic is not on its side. (The distinction between sensible caution about ruin and reflexive flinching at any loss is exactly the difference between risk aversion and loss aversion.)

Here is the part the zero-excess pitch never mentions: you are self-insuring small losses anyway. Claiming £350 on a policy with a £250 excess returns £100 today and typically costs you your no-claims discount (NCD - the premium discount insurers grant for claim-free years) plus higher quotes at renewal for several years. For most drivers that trade is clearly negative, so small claims go unclaimed regardless of the excess level. A low excess buys much less protection than it appears to - you pay every year for cover you would rationally never invoke.

Insurance earns its keep against ruin: the written-off car, the rebuilt kitchen, the liability claim. It is a poor tool for £250 annoyances. Buy the catastrophe cover generously, self-insure the small stuff deliberately, and let the premium saving compound in your own account rather than the insurer's.

• GOV.UK - Vehicle insurance - the legal minimum cover requirements for UK drivers
• MoneyHelper - What is an insurance excess? - the government-backed guidance service's explainer on compulsory and voluntary excess
• Wikipedia - Deductible - the general theory of deductibles (the international term for an excess), including moral hazard and loading