How to Compare UK Petrol and Diesel Prices Before You Fill Up

A cheaper price per litre can still cost more if reaching that forecourt adds a long detour. To compare UK petrol and diesel prices fairly, calculate the cost of the litres you plan to buy at each station, then include the extra journey distance. The Competition and Markets Authority (CMA) publishes road fuel price monitoring information, but any national figures are context, not a promise of what a particular forecourt charges.

Compare the total cost, not just the pump price

Start with the displayed price per litre for the fuel your vehicle uses. Multiply it by the number of litres you expect to buy. Then compare that amount with the same calculation for nearby forecourts.

For a practical comparison, include the cost of the added driving to reach each option. A station several miles away may have a lower pump price but use enough extra fuel to reduce or erase the saving. Consider whether the trip fits a journey you already plan to make; an extra stop on your route has a different cost from a special trip.

Prices can vary by location and station, and displayed prices may change. Check the price close to the time you plan to fill up. A national average, when published, describes a broad market measure and does not establish the current price at every town or forecourt.

Calculate the cost of a fill-up

Use this simple formula:

Litres bought × price per litre = fuel cost

For example, if you buy 40 litres at 145p per litre, the fuel itself costs 5,800p, or £58. If another station charges 142p per litre, the same 40 litres cost £56.80, a difference of £1.20 before accounting for any detour.

To compare stations, repeat the calculation using the same number of litres. This makes the price difference easier to see. If you are comparing a top-up rather than a full tank, use the amount you actually expect to buy.

Then account for the extra journey. One straightforward way is to estimate how many additional miles the detour adds and how much fuel your car uses over those miles. The exact cost depends on your vehicle, traffic and driving conditions, so treat it as an estimate. If the detour’s fuel cost is greater than the pump-price saving, the cheaper forecourt does not save you money overall.

Check nearby prices and allow for changes

Use a fuel finder or price-comparison service to identify options near your route, where available. The CMA’s road fuel price collection is a useful place to find its monitoring publications and related data. Check what each service says about its coverage and how recently prices were updated; a listed price may not match the pump when you arrive.

Before setting off, compare like with like:

• Select the correct fuel type: petrol and diesel prices are different.
• Check the station’s location and whether it is open when you plan to go.
• Look at the price per litre and note when it was last updated, if shown.
• Compare the same number of litres at each station.
• Include the extra distance, traffic and any route you would have driven anyway.

A nearby price can be more useful than a national figure for choosing where to stop today. But even local listings are a guide: confirm the price displayed at the forecourt before filling up.

What the CMA’s fuel information can tell you

The CMA publishes information about UK road fuel and explains its monitoring work. Its GOV.UK collection brings together monitoring publications and related data. This can help readers understand wider price movements and the market context, but it is not a guarantee that a particular station has a specific price at a specific time.

When reading an official price snapshot, check its publication date, the fuel type and what the figure represents. An average or market-wide measure should not be treated as a live local quote. For a buying decision, pair that broader context with a recent local listing and the forecourt’s displayed price.

A quick decision before you fill up

Choose the station with the lowest estimated total for your planned purchase, including any additional driving. If the difference is small, convenience, a route you already need to take and the chance that a listing is out of date may matter more than a few pence per litre.

The useful next check is the current local listing for your fuel type, followed by the price shown at the pump. Recalculate if the price or the number of litres you need changes.

Source: Competition and Markets Authority via GOV.UK