How to save money on petrol and diesel: cut your cost per mile

UK cars are rated in miles per gallon, but fuel is sold by the litre. To find your fuel cost per mile:

Price per litre (in pence) × 4.546 ÷ your miles per gallon = pence per mile

Use the real mpg from your dashboard trip computer, or fill the tank, reset the trip counter and divide miles driven by litres used at the next fill. At an example price of 140p a litre:

Two things move this number: the price you pay per litre, and how many miles you get from each litre. The sections below tackle both. Fuel is only part of the picture, so see the full cost of owning a car too.

Under the Fuel Finder scheme run by the Department for Energy Security and Net Zero, forecourt operators must update their prices within 30 minutes of any change. The data is passed to third-party apps, websites and map services, so you can see current prices along your route rather than relying on old user reports.

Prices for the same fuel can vary a lot within a few miles. Supermarket forecourts are often among the cheapest, and motorway service stations among the most expensive, so fill up before a long motorway journey. Do not drive far out of your way though: a 10-mile detour at 15p a mile costs £1.50, which wipes out a 3p a litre saving on a 50-litre fill.

Supermarket and fuel brand loyalty schemes can give points or money-off vouchers on fuel, and some supermarkets offer fuel discounts when you spend a set amount in store. Only use them if the fuel was already competitively priced; a voucher at a dearer forecourt can leave you worse off. Our guide to fuel discount schemes explains how they work.

Paying with a cashback or rewards credit card earns a little back on every fill, but only if you clear the balance in full every month. Interest on an unpaid balance will cost far more than any cashback.

How you drive and maintain the car often matters more than where you fill up.

Petrol: standard petrol in the UK is E10 (up to 10% bioethanol). Super unleaded (E5) costs more and only makes sense if your car is not E10-compatible or the manufacturer recommends it. Most petrol cars built since 2011 can use E10, and gov.uk has a checker.

Diesel: diesel engines usually return better mpg, which can offset a higher pump price on longer journeys. But lots of short trips stop the diesel particulate filter from cleaning itself, which can lead to warning lights and expensive repairs. If you mostly drive short distances, a regular longer run at steady speed helps, and it is worth bearing in mind when you next change car. Cars using AdBlue need it topping up, and it is usually cheaper bought in larger containers than in small bottles at the pump.

Fuel duty on petrol and diesel is 52.95p a litre until 31 December 2026. Under current plans it rises to 55.95p from 1 January 2027 and to 57.95p from 1 March 2027, although the government has said it will confirm the final rates at Budget 2026. Because VAT at 20% is charged on top of duty, a 3p duty rise adds about 3.6p a litre at the pump if retailers pass it on in full, and the full 5p rise adds about 6p.

Pump prices also move with oil prices and exchange rates, so the actual change could be bigger or smaller. Source: gov.uk, amended fuel duty rates 2026 to 2027.

The cheapest mile is the one you do not drive. Car sharing for the commute, walking or cycling short trips, and checking whether a bus or train is cheaper for regular journeys can all cut your fuel bill. If you are weighing up a change of car, our comparison of electric car running costs vs petrol sets out the numbers.

Once you know your monthly fuel spend, put it in your budget planner and move any saving straight to a car fund for servicing, MOT and tyres. The savings goal calculator shows how quickly that builds, and SYM can nudge you to put the money aside each day.