How this calculator works
The energy the car uses is the miles driven divided by its miles per kWh. Charging at home wastes a little as heat, so the energy from your meter is higher: we divide by one minus the loss. Multiply the home energy by your price per kWh, and any public rapid-charging energy by that price, and add them. The petrol comparison divides the miles by the mpg, multiplies by 4.546 litres to the gallon, and multiplies by the price of a litre.
Worked example: driving 8,000 miles a year at 3.5 miles per kWh uses 2,286 kWh in the battery, or 2,540 kWh from the wall with 10% losses. At 26p that costs £660 a year (£55 a month), or 8.3p a mile. A 45 mpg petrol car uses 178 gallons, which is £1,091 at 135p a litre, so the saving is £431 a year. On a cheap 8p overnight tariff the charging cost falls to £203. Charging half the energy at 75p rapid chargers raises it to £1,187, and driving 12,000 miles costs £990. Adding 42 kWh to a 60 kWh battery (10% to 80%) takes about 6.3 hours on a 7.4 kW wallbox, 20 hours on a 13 A socket, and about 50 minutes at a 50 kW rapid charger, for 147 miles of range.
Yearly charging cost by electricity price (8,000 miles, 3.5 miles per kWh, 10% losses)
Home charging only. Compare with the petrol figure in the results.
| Price per kWh | Per year | Per month | Per mile |
|---|---|---|---|
| 8p | £203 | £17 | 2.5p |
| 15p | £381 | £32 | 4.8p |
| 20p | £508 | £42 | 6.3p |
| 26p | £660 | £55 | 8.3p |
| 30p | £762 | £63 | 9.5p |
| 35p | £889 | £74 | 11.1p |
Tips before you buy
- Use the miles per kWh from your own car if you can: the trip computer shows it. Winter driving and motorway speeds use 20 to 30% more energy than the official figure.
- A cheap overnight tariff is the biggest saving. If the car is home overnight, charge in the off-peak window.
- Public rapid chargers cost several times as much per kWh as home charging, so the share you charge there matters a lot.
- Charging losses are about 10% at home, so the energy from your meter is more than the energy that reaches the battery.
- A home wallbox needs a dedicated circuit and is usually fitted by an approved installer. A three-pin socket is slow and should be used only occasionally.
Tools & materials for this project
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Frequently asked questions
How much does it cost to charge an electric car at home?
At 26p per kWh, about £660 a year for 8,000 miles (£55 a month), which is 8.3p a mile. On an 8p overnight tariff it is about £203 a year.
How much does it cost to charge an EV from 10% to 80%?
A 60 kWh battery takes 42 kWh, which costs about £12.13 at home at 26p, with 10% losses. On a rapid charger at 75p it costs about £31.50.
Is an electric car cheaper than petrol?
Usually, if you charge at home. The same 8,000 miles cost about £1,091 in a 45 mpg petrol car and £660 to charge at home, a saving of £431 a year. Using public rapid chargers for half the energy cuts the saving to £-96.
How long does it take to charge an electric car?
About 6.3 hours to add 42 kWh on a 7.4 kW home wallbox, about 20 hours on a 13 A three-pin socket, and under an hour at a rapid charger.
How many miles per kWh does an electric car do?
Most manage about 3 to 4.5 miles per kWh. Small cars do better, large SUVs and vans worse, and cold weather and fast motorway driving use more.
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