To compare an electric car with petrol or diesel, work out the cost per mile for each. For petrol or diesel: pence per litre × 4.546 ÷ mpg. For an EV: pence per kWh ÷ miles per kWh. At home electricity prices an EV usually comes out well ahead. If you rely on public rapid chargers, it can cost more per mile than petrol.
All prices below are example figures to show how the sums work. Fuel and electricity prices move, so swap in what you actually pay.
Petrol and diesel cost per mile
UK fuel is sold in litres but economy is quoted in miles per imperial gallon, and an imperial gallon is 4.546 litres. So:
Example: petrol at 150p a litre in a car doing 45 mpg. 150 × 4.546 = 681.9p per gallon. Divide by 45 and you get 15.2p a mile.
Use your real mpg, not the brochure figure. Brim the tank, zero the trip, brim it again next time and divide miles by gallons. The MPG calculator does that for you.
Electric cost per mile
Most EVs show miles per kWh on the dash or in the app. If yours shows kWh per 100 miles, divide 100 by that figure: 28 kWh per 100 miles is about 3.6 miles per kWh. Small cars often manage 4 or more in mild weather, big SUVs 2.5 to 3. Everything drops in winter and at motorway speeds.
The price per kWh is where EV costs swing wildly:
| Example price per kWh | At 3 miles/kWh | At 3.5 miles/kWh | At 4 miles/kWh |
|---|---|---|---|
| 7p (example overnight EV tariff) | 2.3p | 2.0p | 1.8p |
| 25p (example standard home rate) | 8.3p | 7.1p | 6.3p |
| 55p (example public fast charger) | 18.3p | 15.7p | 13.8p |
| 80p (example public rapid charger) | 26.7p | 22.9p | 20.0p |
Charging also loses a little energy as heat, so your meter will show slightly more than the battery takes in. Your standing charge is paid whether you charge or not, so leave it out of the per-mile sum.
Worked comparison: 8,000 miles a year
Using example prices: petrol at 150p a litre, diesel at 155p, home electricity at 25p per kWh, an overnight EV tariff at 7p and rapid charging at 80p. The petrol car does 45 mpg, the diesel 55 mpg and the EV 3.5 miles per kWh.
| How you fuel it | Per mile | 8,000 miles |
|---|---|---|
| Petrol, 45 mpg, 150p/litre | 15.2p | £1,212 |
| Diesel, 55 mpg, 155p/litre | 12.8p | £1,025 |
| EV, all at home on 25p | 7.1p | £571 |
| EV, all on an overnight tariff at 7p | 2.0p | £160 |
| EV, 80% home at 25p, 20% rapid at 80p | 10.3p | £823 |
| EV, all on rapid chargers at 80p | 22.9p | £1,829 |
The pattern holds whatever the exact prices. Charge at home, especially on a cheap overnight rate, and an EV is much cheaper to fuel. Rely on rapid chargers and it can cost more than petrol. With these example figures, the break-even point is about 53p per kWh. Above that, the 45 mpg petrol car is cheaper per mile.
Vehicle tax
Electric cars have paid vehicle tax since 1 April 2025. For the 2026/27 rates on GOV.UK:
- An electric car registered on or after 1 April 2025 pays £10 in the first year, then the standard rate of £200 a year.
- One registered between 1 April 2017 and 31 March 2025 pays the £200 standard rate.
- Electric cars registered from 1 April 2025 with a list price over £50,000 pay an extra £440 a year for five years from the second year of tax. For petrol and diesel cars the threshold is £40,000.
So for a typical post-2017 car, petrol, diesel and electric now pay the same standard rate. Check your own car with the car tax calculator.
Looking further ahead, the government has announced a pay-per-mile charge for electric cars (3p a mile) and plug-in hybrids (1.5p a mile) from 1 April 2028. At the time of writing it still needs legislation, so it isn't in the figures above. At 3p a mile, 8,000 miles would add £240 a year.
Insurance and servicing
These depend so much on the car, the driver and the postcode that any average would mislead. EVs have fewer moving parts and no oil changes, but tyres can wear faster on heavier cars, and insurance varies by model. Get real quotes for the specific cars you're comparing before deciding.
Running your own numbers
- Find your annual mileage from your last two MOT certificates.
- Work out the petrol or diesel cost per mile with your real mpg and local pump price.
- Work out the EV cost per mile with your tariff and a realistic split between home and public charging.
- Multiply each by your mileage and compare.
The fuel cost calculator handles petrol and diesel trips, and the EV charging cost calculator compares home and rapid charging against a petrol car.
Last reviewed October 2026.