Fuel Cost Calculator

A fuel cost calculator works out how much petrol or diesel a journey will cost based on three inputs: distance, fuel economy and pump price. In 2025/26 UK average petrol prices sit around £1.40 per litre and diesel about £1.45 per litre, with motorway service stations typically 10-15p/litre more expensive and supermarket forecourts (Asda, Sainsbury’s, Morrisons, Tesco) usually 3-5p/litre cheaper than the national average. Fuel duty in the UK is 52.95p per litre — frozen since March 2011 and again confirmed frozen in the Autumn 2025 Budget — plus 20% VAT charged on the duty-inclusive price. So roughly 60% of every petrol pound goes to HMRC. The formula the calculator uses is: cost = (distance in miles ÷ MPG) × 4.546 × price per litre. The 4.546 is the conversion from imperial gallons (used in MPG) to litres (used in UK pricing). For a 200-mile trip at 45 MPG and £1.40/litre that gives (200 ÷ 45) × 4.546 × 1.40 = £28.30, or 14.2p per mile. Sometimes split across passengers: a 4-person trip costs each passenger about £7.07. The calculator also supports L/100km input for European-spec readings — 282.5 ÷ MPG = L/100km. Real-world MPG is almost always lower than the manufacturer’s official WLTP figure on the V5C and brochure. Plan with real-world numbers: average 35-40 MPG for petrol family cars, 45-55 MPG for diesel, 55-70 MPG for petrol-hybrid in urban driving, 75-90 mpg-e for plug-in hybrids running mostly on electric, and 3.5-4.5 miles/kWh for full EVs. Confit.com and HonestJohn’s Real MPG database hold thousands of real-world readings — typically 15-25% below WLTP for petrol/diesel. What changes the bill the most. Speed: dropping motorway cruise from 80 mph to 65 mph improves MPG by roughly 20%. Tyre pressure: 5 psi under-inflated reduces MPG by about 2%. Roof boxes/bikes add 10-25% to motorway consumption due to aerodynamic drag. Aircon adds about 5%. Stop-start city driving can halve highway MPG. The calculator does not model these multipliers — enter your realistic MPG to get accurate journey costs. For pence-per-mile across a year use the Car Running Cost Calculator; for MPG measurement from fuel receipts use the MPG Calculator; for EV vs petrol comparison use the Electric Car Savings Calculator.