Supermarket Fuel Comparison Calculator
Compare two petrol stations and see whether driving to the cheaper one is actually worth it, once the fuel cost of getting there is taken into account.
Estimate only. Fuel prices change daily and vary by station and region — treat these figures as illustrative. Check current local prices before deciding where to fill up.
Not worth the detour
£1 Net loss per fill
- Pump-price saving per fill
- £1
- Detour fuel cost
- £2
- Net loss per fill
- £1
Things to weigh up
- Use a live fuel-price checker (like PetrolPrices.com or a supermarket's app) before you drive — forecourt prices change daily and the gap you're comparing may already have closed.
- The best value is almost always filling up somewhere you're already driving past, not making a special trip purely to save a few pence a litre.
- If you're a Costco (or similar warehouse club) member, its fuel is often cheaper again than either supermarket — worth checking with our Costco Fuel Savings calculator.
- A bigger tank fill makes a small per-litre saving more worthwhile, because the detour cost is fixed but the saving scales with every litre you buy.
Why the 'obvious' saving can be a loss
Multiplying the pence-per-litre gap by your tank size looks like free money, but getting to the cheaper station and back also costs fuel. We convert your one-way detour distance into a return trip, work out how many litres that burns at your mpg (1 UK gallon = 4.54609 litres exactly), and price it at your usual station's rate. Subtract that from the pump-price saving and you get the real, net saving — which can easily turn negative on a short fill with a long detour.