Fuel Cost Calculator

How to Estimate Fuel Costs for Any Journey

Fuel is the single largest variable cost of driving in the UK, and the gap between paper estimates and what your debit card actually shows after a fill-up keeps widening. According to RAC Fuel Watch, typical 2025 forecourt prices have hovered between roughly 135-145p per litre for petrol and 140-150p per litre for diesel, with supermarket forecourts (Asda, Tesco, Morrisons, Sainsbury's) usually 4-8p cheaper than motorway service stations. Diesel almost always carries a premium of 5-10p per litre over petrol despite producing less CO2 per mile, which is a quirk of UK wholesale margins rather than raw production cost.

Most of what you pay at the pump is tax. Fuel duty sits at 52.95p per litre on standard unleaded and diesel — the so-called 'temporary' 5p cut introduced in March 2022 was extended again in the Spring Budget 2024 and remains in place through 2025. Then VAT at 20% is applied on top of the pump price including the duty, meaning roughly 60% of every litre you buy is government revenue rather than fuel. This is why pump prices barely fall when oil markets dip: the tax floor stays fixed.

Electric vehicles change the maths entirely. Charging at home on a standard variable Ofgem-capped tariff costs around 28-30p per kWh, while public rapid charging on networks like Instavolt, Osprey, BP Pulse or Ionity typically lands at 70-80p per kWh according to Zap-Map's quarterly tracking. That 2-3x premium for public charging means an EV that looks unbeatable on home electricity becomes uncompetitive with a 60-MPG diesel on a motorway road trip. Hybrids sit in the middle, with self-charging full hybrids like the Toyota Prius family routinely achieving 55-65 MPG in mixed UK driving.

This calculator handles all of these scenarios. Enter your real-world MPG (not the WLTP brochure figure), the current price you're seeing at the pump or the kWh rate from your electricity bill or charging app, and the trip distance, and you get an honest cost in pounds. It is genuinely the most useful 30 seconds you can spend before signing a finance agreement, accepting a job with a longer commute, or planning a 600-mile holiday drive to Cornwall.

How to Calculate Petrol or Diesel Cost per Trip

Enter the trip distance in miles or kilometres, your vehicle's fuel efficiency (MPG, km/L, or L/100km), and the current pump price per litre or gallon. Click Calculate to see the fuel required and total cost in pounds.

1. Enter the total distance of your journey in miles (or kilometres if you prefer metric).
2. Add a return-leg distance if it's a round trip — the calculator does not assume two-way unless you double it.
3. Input your vehicle's real-world fuel efficiency. Use MPG for UK figures, L/100km if you prefer European format, or km/L.
4. Enter the current pump price in pence per litre (135-150p is typical UK 2025) or pounds per gallon.
5. For an EV, switch to kWh and enter your home tariff (28-30p) or rapid-charge rate (70-80p).
6. Click Calculate to see fuel volume needed and the total cost in pounds.
7. Adjust efficiency by 10-15% downward to model winter, motorway speed, or hilly terrain conditions.

Fuel Cost Formula: Distance ÷ MPG × Price per Litre

The formula used: Fuel Needed = Distance / Fuel Efficiency; Total Cost = Fuel Needed × Price per Litre (or Gallon)

Fuel Cost Estimates for 50, 100, and 300 Mile Trips

A 300-mile UK trip in a car that does 45 MPG with petrol at 142p/litre: 300 ÷ 45 = 6.67 UK gallons = 30.31 litres. Cost = 30.31 × £1.42 = £43.04.

When to Calculate Fuel Costs (Road Trips, Commutes, Fleet)

Run this calculator before you sign anything that locks you into long-term fuel exposure. Buying or PCP-financing a car is the obvious one — the difference between a 35 MPG SUV and a 55 MPG estate over the DfT-average 7,400 miles per year and a 3-year ownership cycle is roughly £1,500 in fuel alone, before you even consider VED bands or insurance group differences. That gap often outweighs the £20-40/month PCP saving on the bigger car.

Use it before accepting a job with a longer commute. A move from a 5-mile to a 25-mile each-way drive doesn't just multiply your fuel cost by five; it multiplies wear, insurance mileage band, and your tax-deductible AMAP entitlement (if self-employed). Plug both commutes into the calculator alongside the salary uplift to see whether the new role actually leaves you better off net of driving cost.

It is also essential before a UK road-trip holiday. A West Country fortnight covering 800-1,200 miles in a family car will cost £100-180 in petrol depending on MPG and pump price — easily a third of a budget hotel night. For EV drivers, the calculator helps you decide whether to slow-charge overnight at a hotel (often free or £5 flat) versus rapid-charging mid-route (£30-50 a session). And for company-car drivers, it lets you sanity-check the HMRC Advisory Fuel Rate (AFR) reimbursement your employer pays against what you actually spent — AFR is published quarterly by HMRC and varies by engine size and fuel type, so the gap between AFR and real cost can be material in months when oil prices spike.

MPG, Litres per 100 km, and Fuel Efficiency

Petrol, Diesel, Hybrid, and EV: Cost-Per-Mile Compared

Tips to Reduce Your Fuel Costs

• Use supermarket forecourts (Asda, Tesco, Morrisons, Sainsbury's) — they undercut branded BP/Shell stations by 4-8p per litre on average, and motorway services by 15-20p.
• Stick to 60-65 mph on motorways. Cruising at 80 mph instead of 65 mph increases fuel burn by 20-25% because air resistance rises with the square of speed.
• Check tyre pressures monthly. Underinflation by 10 PSI knocks 3-5% off MPG and chews through tyres faster.
• Strip the roof rack, roof box and bike carrier when you're not using them — they each cost 10-25% MPG at motorway speeds due to drag.
• Use a fuel price app (PetrolPrices, Confused.com Fuel Price Checker) to find the cheapest forecourt within a 2-mile radius before you fill up.
• Avoid premium petrol unless your manual specifically requires it. For most cars, super unleaded delivers no measurable MPG benefit and costs 15-20p more per litre.
• If you're a company-car driver, claim Advisory Fuel Rate (AFR) for business mileage rather than paying for fuel out of pocket. HMRC publishes new rates every three months.
• If you drive your own car for work, claim the full HMRC AMAP rate (45p/mile up to 10,000 miles) on your Self Assessment — it's tax-free and almost always exceeds your actual fuel cost.
• For EV owners: switch to a smart EV tariff like Octopus Intelligent Go or EDF GoElectric, where overnight rates can drop to 7-10p/kWh — a 70%+ saving versus the standard variable rate.

Fuel Calculation Errors Using Mixed Units

• Confusing fuel cost with HMRC AMAP. AMAP (45p first 10,000 miles, 25p above) covers all running costs — fuel, insurance, depreciation, servicing, MOT, tyres — not just fuel. The fuel-only cost is typically 12-18p/mile, so the AMAP surplus exists to compensate for everything else.
• Forgetting that AMAP rates have been frozen since 2011. The 45p rate hasn't moved in over a decade despite cumulative UK inflation of around 40%. The real-terms value of a business mile claim has fallen by roughly a third — flag this when reviewing whether your employer's reimbursement is fair.
• Using the brochure WLTP MPG figure rather than your actual trip-computer or tank-to-tank measurement. WLTP is 10-15% optimistic for most drivers in real conditions.
• Mixing up MPG (higher is better) and L/100km (lower is better) — they move in opposite directions, so a 'better' figure looks like a different change in each system.
• Forgetting the return leg of a round trip — a 'Manchester to London' trip is 200 miles one way but 400 miles round trip.
• Ignoring the difference between UK gallons (4.546 litres) and US gallons (3.785 litres) when reading American review sites or US-import car specs. A 50 US MPG car is only 41.6 UK MPG.
• Forgetting Clean Air Zone (CAZ) and ULEZ charges in Birmingham, Bristol, Sheffield, Bradford and London — a non-compliant diesel can cost £8-12.50 per day on top of fuel.
• Not adjusting for winter: cold engines, sub-zero temperatures and shorter trips routinely cut MPG by 10-20% from December to February.
• Trying to claim AMAP and a fuel receipt for the same journey on Self Assessment — HMRC explicitly prohibits double-counting. Pick one method per vehicle per tax year.