Fuel Cost Calculator

Spend Less on Petrol Without Changing Your Car

The biggest factor in your fuel bill isn't the price at the pump — it's how you drive. Small changes in habits can save hundreds of pounds a year without any special equipment or modifications.

1. Keep a steady pace. Aggressive acceleration and hard braking can use up to 40% more fuel. Ease off the pedals and let momentum do the work.
2. Slow down on motorways. Most cars reach peak efficiency between 45 and 65 mph. Every 10 mph above that range costs you noticeably more per mile.
3. Check tyre pressure monthly. Under-inflated tyres increase rolling resistance and can reduce economy by up to 3%.
4. Ditch extra weight. A roof rack or box adds drag even when empty and can cut efficiency by around 5%. Remove it when you don't need it.
5. Combine errands. A warm engine is far more efficient than a cold one. Several short trips from a cold start use significantly more fuel than one longer loop.
6. Stay on top of servicing. A clean air filter, fresh spark plugs, and the correct oil grade all help your engine run as efficiently as possible.
7. Use air-con wisely. Below about 40 mph, open windows are cheaper. Above that speed, the drag from open windows costs more than running the air-con.

Why Petrol Prices Change

Several layers sit between crude oil and the price you see on the forecourt:

• Crude oil (50–60% of the pump price). Global benchmarks like Brent crude set the baseline. Supply decisions by OPEC and geopolitical events can move prices overnight.
• Fuel duty and VAT. The UK levies around 52.95p per litre in fuel duty plus 20% VAT on top. These taxes make up a significant share of what you pay.
• Refining and distribution. Turning crude into usable petrol or diesel and transporting it to forecourts adds its own margin, which fluctuates with demand and refinery capacity.
• Seasonal demand. Summer holidays and bank-holiday weekends push consumption up, and prices often follow. Filling up midweek or outside peak travel periods can help.

How Fuel Cost Is Calculated

The basic formula is straightforward:

Fuel cost = (distance ÷ fuel efficiency) × price per litre

Imperial example (miles & mpg):

• Journey: 300 miles
• Efficiency: 40 mpg
• Fuel needed: 300 ÷ 40 = 7.5 UK gallons = 7.5 × 4.546 = 34.1 litres
• Cost: 34.1 × £1.45/L = £49.40

Metric example (km & L/100 km):

• Journey: 500 km
• Efficiency: 7 L/100 km
• Fuel needed: 500 × (7 ÷ 100) = 35 litres
• Cost: 35 × £1.45/L = £50.75

Pop your numbers into our free Fuel Cost Calculator above and get an instant answer — no maths required.