Why the cheaper pump price does not tell the whole story
Annual fuel cost equals driving miles ÷ UK MPG × 4.54609 litres per imperial gallon × price per litre. We calculate E10 and E5 separately using the actual MPG values you enter.
What does the government say about E10?
The Department for Transport says E10 can reduce fuel economy by around 1%, although drivers are unlikely to notice this in everyday driving. A small MPG improvement does not automatically offset a much higher price for E5.
Can your vehicle use E10?
Cost is not the only consideration: check whether the manufacturer approves E10 for your petrol vehicle. Incompatible older vehicles and some motorcycles should use the appropriate E5 grade. Use the official UK government E10 checker before switching fuels.
Compare fuel prices fairly
Record the real pump prices at the same point in time, and compare comparable journeys and driving conditions. E5 super unleaded often has a higher octane rating; that does not guarantee a better MPG reading for every car. Repeat the comparison across multiple tanks if practical.
How to interpret the break-even MPG
The break-even figure is the E5 MPG required for its cost per mile to equal E10 at the prices you entered. If your actual E5 MPG is lower than that, E10 costs less per mile; if higher, E5 costs less.
Check compatibility first
Some older petrol vehicles are not compatible with E10. This calculator is not an E10 vehicle-compatibility checker, and petrol grade choice must follow the manufacturer’s requirements.
Questions drivers ask
Does E5 give every car better MPG?
No. The result depends on the engine and actual driving conditions. Use your measured MPG rather than assuming a universal percentage.
Can I use E10 in an older car?
Check the official government compatibility tool or your vehicle manufacturer. Do not make a choice based on price alone.
Reference: Department for Transport: E10 petrol explained. Worked figures are illustrative and editable. Last reviewed 11 October 2026.