EV charging cost calculator

Charging losses mean you always pay for more kilowatt-hours than the battery actually receives.

You pay for more than the battery receives

Charging is not lossless. Energy is lost in the charger, in the cabling, and as heat in the battery itself, and more is spent running the thermal management system while charging. Typical AC home charging runs about 85-90% efficient; DC rapid charging is usually a little better at the battery but the losses shift elsewhere.

The practical consequence is that a 10% loss means paying for roughly 11% more energy than the battery gains — 64 kWh into the pack costs you about 71 kWh on the meter. Any cost-per-mile figure that ignores this understates the real number, and most published ones do.

Cost per mile is the number that matters

Comparing an EV to a petrol car by cost per charge is meaningless, because the ranges differ. Cost per mile or per 100 km is the honest comparison.

At 17 kWh/100 km and 28p per kWh, allowing for charging losses, that is about 5.3p per km or roughly 8.5p per mile. A petrol car doing 40 mpg at £1.45 a litre costs about 16.5p per mile. The gap is real, but it depends almost entirely on your electricity tariff.

Tariff matters more than the car

The single biggest variable in EV running costs is when and where you charge:

Overnight EV tariff — often 7-10p per kWh, sometimes less. This is where the dramatic savings come from.
Standard domestic rate — typically 25-30p per kWh. Still cheaper than petrol, but not dramatically.
Public rapid charging — commonly 60-85p per kWh. At the top of that range, an efficient EV can cost about the same per mile as a diesel.

An EV charged exclusively on public rapid chargers loses most of its running-cost advantage. The economics assume home or workplace charging on a cheap tariff.

Why 20-80% is the default here

Lithium-ion cells age faster at very high and very low states of charge, so routine charging to 80% and avoiding deep discharge extends usable battery life. Most manufacturers now recommend it explicitly for daily use, reserving 100% for long trips.

On DC rapid chargers there is a second reason: charging speed tapers sharply above roughly 80% to protect the cells. The last 20% can take as long as the first 60%, which is why the linear time estimate here becomes unrealistic on a rapid charger.

Things that make it worse in practice

Cold weather is the big one. Below freezing, consumption can rise 20-30% from cabin heating and reduced battery efficiency, and charging is slower until the pack warms. Motorway speeds hurt disproportionately because aerodynamic drag rises with the square of speed. Roof boxes, towing and hills all add more than people expect.

Common questions

How much does it cost to charge an electric car at home?

Multiply usable battery capacity by your price per kWh, then add roughly 10% for charging losses. A 64 kWh battery at 28p per kWh costs about £20 for a full charge from empty.

Why do I pay for more kWh than the battery holds?

Charging loses energy as heat in the charger, cables and cells, plus power for thermal management. Home AC charging is typically 85-90% efficient, so you pay for about 11% more than the battery gains.

Is it cheaper to charge at home or at a public charger?

Home, substantially. A cheap overnight EV tariff can be 7-10p per kWh against 60-85p at a public rapid charger. On rapid charging alone, an EV can cost roughly the same per mile as a diesel.

Why is 80% the recommended charge limit?

Lithium-ion cells degrade faster when held at high states of charge, so daily charging to 80% prolongs battery life. On rapid chargers the rate also tapers sharply past 80%, so the last fifth is disproportionately slow.