Fuel price · petrol · diesel
Fuel price calculator – the rise in per cent and in pounds
The change in the litre price as a percentage only tells you half the story. This calculator also tells you what the change means for one fill-up, for a journey and over a year – the figure that shows up in the household budget.
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Per cent or pence – which tells you more?
When the litre price rises from 1.429 to 1.489 pounds, the rise is 6 pence (about 4.2%). The percentage is
useful for comparison, but in daily life it's the pounds that matter. On a fifty-litre tankful the rise is £3.00, and
for someone driving 20,000 km a year in a car using 6.5 l/100 km it is
0.06 × 1,300 l = £78 a year.
price change % = (new − old) / old × 100
journey consumption = consumption (l/100 km) / 100 × distance (km)
UK pump prices are usually shown in pence per litre (e.g. 148.9 p/l). Enter the same figure in pounds (1.489) here – it's the same price.
Fuel cost at different consumption rates
| Consumption | 100 km | Commute 40 km/day, 20 days | 20,000 km/year |
|---|---|---|---|
| 4.5 l/100 km | £6.71 | £53.64 | £1,341 |
| 6.5 l/100 km | £9.69 | £77.48 | £1,937 |
| 8.0 l/100 km | £11.92 | £95.36 | £2,384 |
| 10.0 l/100 km | £14.90 | £119.20 | £2,980 |
The commute column represents 800 kilometres a month, i.e. 40 kilometres a day over 20 working days. If you drive the trip as a return journey, multiply by two. In winter the real consumption is typically clearly higher than stated, as it is on short trips when the engine doesn't warm up. So use your own car's actual average consumption if you want a realistic figure.
What makes up the fuel price
Most of the pump price is tax: fuel duty and, on top of that, VAT at the standard rate. So a change in VAT or fuel duty shows in the price straight away, whereas a change in the crude oil price reaches the pump with a delay.
Because VAT is calculated last, on top of the duty, the VAT amount also rises as the price rises. You can work out a breakdown of the net and gross price with the VAT calculator by entering the pump price and choosing the standard rate.
Petrol, diesel or electric – a comparison per 100 kilometres
The most reliable way to compare fuels is the cost per hundred kilometres, because a litre price and a kilowatt-hour price aren't directly comparable. The method is the same for both: consumption multiplied by the price of the energy.
| Fuel | Consumption / 100 km | Unit price | Cost / 100 km |
|---|---|---|---|
| Petrol | 6.5 l | £1.49/l | £9.69 |
| Diesel | 5.2 l | £1.55/l | £8.06 |
| Electric, home charging | 18 kWh | £0.25/kWh | £4.50 |
| Electric, rapid charging | 20 kWh | £0.75/kWh | £15.00 |
The figures are examples, not forecasts: the price of electricity varies by time of day and tariff, and in winter an EV's consumption rises clearly. The idea of the comparison stays the same, though – always work out the same journey with the same logic, and don't compare a litre price with a kilowatt-hour price.
The total cost also includes insurance, servicing, tyres, vehicle tax and depreciation. You can get the size of the depreciation as a percentage with the percentage change calculator by entering the purchase price and the current value.
Three ways to cut your fuel bill
- Keep tyre pressures right. Under-inflated tyres raise consumption by a few per cent. Check the pressures monthly – it's free.
- Clear out dead weight. A roof rack and permanently carried extra weight show up in consumption, especially at motorway speeds.
- Keep a steady speed. Dropping ten km/h on the motorway lowers consumption noticeably, because air resistance grows with the square of speed.
Work out the effect yourself: enter your current and target consumption on the calculator's Cost of a journey tab over the same distance and compare the results.
Is it worth driving further for a cheaper station?
A classic mistake is driving five kilometres to save three pence a litre. On a forty-litre fill-up the saving is £1.20. A ten-kilometre round trip in a car using 6.5 l/100 km burns 0.65 litres, i.e. about £1.00 – the saving all but disappears. The rule: only drive further if the trip is short or the price difference is at least 5–10 pence a litre.
The basics of fuel-cost calculation
A price change is calculated from the old price. The journey cost is consumption times distance times the litre price.
Formulas and examples
Price change as a percentage
(new − old) / old × 100Example
1.429 → 1.489 £/l: +4.2%, i.e. 6 pence a litre.
Note
Per cent suits comparison, pounds show the impact.
Journey consumption
consumption / 100 × distanceExample
6.5 l/100 km and 320 km: 20.8 litres.
Note
Use the car's real trip-computer average, not the maker's figure.
Journey cost
litres × litre priceExample
20.8 l × 1.489 £: £30.97, i.e. £9.69 per 100 km.
Note
Add tolls or parking separately.
Cost per passenger
journey cost / passengersExample
£30.97 / 4: £7.74 each.
Note
Sharing a car is the cheapest way to cut the per-person cost.
Concepts and classification
| l/100 km | A consumption unit; the UK also uses miles per gallon (mpg). |
|---|---|
| Litre price | The pump price, including fuel duty and VAT. |
| Average consumption | Actual consumption, typically higher than stated. |
| Tankful | The tank capacity in litres. |
| Cost per 100 km | The most comparable figure across different fuels. |
Limitations of the calculator
- Winter, town driving and a load raise consumption clearly.
- The calculator does not take account of insurance, servicing, tyres or depreciation.
- An EV's comparison figures depend on the charging method and electricity tariff.
- The fuel tax structure is not broken down – use the VAT calculator for a breakdown.
How up to date the information is
When it was checked
Content and the figures used were checked on 12 August 2026.
Disclaimer
The calculator gives a mathematical result from the numbers you enter. It is not an official decision, an offer or professional advice. See the terms of use.
Topics
This calculator belongs to the following topic areas. On the topic page you'll find all the calculators and guides on the same theme in one place.
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Frequently asked questions about the fuel price calculator
How do I work out a fuel price rise as a percentage?
(new price − old price) / old price × 100. For example 1.429 → 1.489 £/l is 0.06 / 1.429 × 100 = 4.2%. The calculator also shows the impact in pounds per fill-up and per year.
How do I work out the fuel cost of a journey?
Multiply consumption per 100 km, the distance and the litre price: consumption / 100 × km × £/l. For example 6.5 l/100 km, 320 km and 1.489 £/l is 20.8 l × 1.489 = £30.97.
How much of the fuel price is tax?
Most of the pump price is fuel duty plus VAT at the standard rate. VAT is calculated last, on top of the duty, so the VAT amount also rises when the price rises. You can get the net price with the VAT calculator.
Is it worth driving further for cheaper fuel?
Work out the driving cost first. A ten-kilometre round trip in a car using 6.5 l/100 km burns about 0.65 litres. If the saving on the fill-up is smaller than that, the trip isn't worth it.
Why is real consumption higher than the stated figure?
Winter, short trips, town driving, a load and tyre pressure all raise consumption. Use your own car's trip-computer average in the calculator so the result matches reality.