Is it worth driving further for cheaper petrol?

The short version

A car doing 50 to the gallon burns about a litre every 11 miles. At 174p a litre, a five-mile detour each way uses roughly £1.58 of fuel. Spread over a 50-litre fill, that means you need to be saving about 3p a litre just to break even on the fuel — before the time it takes, and before the wear on the car.

Nearby is almost always worth it. Across town almost never is. The line sits closer than most people assume, and it moves closer as fuel gets dearer.

The break-even table

How much cheaper the other forecourt has to be, per litre, before a detour pays for the fuel it burns. Petrol at 174p, a 50-litre fill:

Supermarket forecourts are often a few pence under the branded ones, so a two or three-mile hop usually clears the bar comfortably. A ten-mile one needs a 6p to 8p gap, which is a wide spread and not something you find most weeks.

Higher prices make the detour worse, not better

This is the part that catches people out. When fuel gets expensive the instinct is to shop harder — but the drive to the cheaper pump is itself paid for in fuel, at the dearer price. The more a litre costs, the more your detour costs, and the bigger the saving has to be to justify it.

Diesel at 199p a litre makes a five-mile detour cost about £1.81 rather than £1.58. The threshold moves from 3.2p to 3.6p a litre. Not dramatic, but it moves the wrong way from what intuition says.

The two costs the fuel maths leaves out

Your time. Ten miles of town driving plus the queue is realistically 25 to 35 minutes. On the table above that detour saves £3.15 on a full tank, if you find a 6.3p gap. Call it £6 an hour — below the minimum wage, for driving.

The car. Fuel is not the only thing a mile costs. HMRC's approved mileage rate is 45p a mile, which covers tyres, servicing, depreciation and insurance as well as fuel. On that basis a ten-mile round trip costs £4.50 against £1.60 saved. That figure overstates the marginal cost, because insurance and most depreciation happen whether you drive or not — but even at a conservative 20p a mile the ten-mile round trip costs £2.00 to save £1.60.

The car cost calculator works out what your own car costs per mile, which is the number that actually applies here.

What changed on 8 October

Google Maps now shows live pump prices at UK forecourts. The data comes from Fuel Finder, the scheme that requires stations to report any price change within 30 minutes — the same feed behind PetrolPrices, RAC Fuel Watch and others. The Department for Energy Security and Net Zero puts it at about £40 a year for a car-owning household.

Forty pounds a year across roughly twenty fills is £2 a fill, or about 4p a litre on a 50-litre tank. Which is to say: the official estimate assumes you find a station a few pence cheaper and that it is close by. It does not assume you drive across town.

The bigger number is the duty rise

Fuel duty has been held at 52.95p a litre since May, when the 5p cut was extended, but only to 31 December. The published rates for 2027 take it to 55.95p from 1 January and 57.95p from 1 March. VAT is charged on top of duty, so at the pump that is roughly 3.6p a litre more in January and 6p by March.

At 7,000 miles a year, 6p a litre is about £38 — which is most of the £40 the map is meant to save. The government says it will confirm the rates at the Budget on 28 October. We are tracking it here.

So what is the rule?

• On your route, always. A cheaper station you pass anyway costs nothing to use.
• Within two or three miles, nearly always. You need barely 1p to 2p a litre to clear it.
• Five miles, only on a real gap. Around 3p to 4p a litre, and only if you are filling up properly.
• Ten miles or more, almost never. You need 6p to 8p a litre, plus half an hour, plus the wear.
• Never on a quarter tank. The saving scales with litres bought; the detour costs the same either way.

The honest summary is that shopping around for fuel is worth doing and not worth travelling for. The app in your pocket is useful because it tells you which of the stations you were already going past is cheapest — not because it is worth chasing one across a city.

Frequently asked

This is general information, not financial advice. The figures WealthR shows are illustrative and depend on the inputs you provide. For decisions involving significant sums, please consult a qualified FCA-regulated financial adviser.