Electric car charging feels cheap until you try to work out exactly what one charge costs. The battery size is in kilowatt-hours, the price is per kilowatt-hour, and the charge rarely goes from empty to full, so the maths needs a few steps. This calculator does those steps for you. Enter your battery size, the charge range, the charging losses, and your electricity price, and it returns the energy drawn from the wall and the cost of that one home charge.
The key idea is that you pay for energy drawn from the wall, not energy stored in the battery. Charging is not perfectly efficient: some energy becomes heat in the charger, the cable, and the battery itself. A typical home AC charging loss of about 10 percent means that storing 36 kilowatt-hours in the battery draws about 39.6 kilowatt-hours from the wall. Ignoring losses understates every charge by that margin, which adds up over a year of regular charging.
Here is a worked example. A 60 kilowatt-hour battery charged from 20 percent to 80 percent needs 60 percent of its capacity, which is 36 kilowatt-hours stored. With 10 percent charging losses, the wall draw is 39.6 kilowatt-hours. At 0.30 per kilowatt-hour, that charge costs 11.88. If that charge gives 300 kilometres of range, the cost is 3.96 per 100 kilometres. Compare that with the petrol cost for the same distance, and the running-cost advantage of home charging becomes concrete instead of vague.
Your electricity tariff decides whether that advantage is large or small, so enter the price you actually pay. A cheap overnight tariff can halve the cost of the same charge compared with a standard daytime rate, which is why many electric car owners schedule charging for the night. A public fast charger, by contrast, can cost two or three times a home rate per kilowatt-hour, plus possible idle fees if you stay plugged in after charging finishes. This calculator models home charging; public charging needs its own, much higher price.
Battery behaviour adds small wrinkles worth knowing. Charging slows near full, and most makers advise daily charging to around 80 percent rather than 100 percent, to protect long-term battery health. Cold weather also raises losses and can reduce range, because the battery warms itself and the cabin heating draws power. None of this changes the basic formula, but it explains why two identical charges in summer and winter can cost slightly different amounts and give slightly different range.
To compare cars or tariffs fairly, use the cost per 100 kilometres, not the cost per charge. A large battery costs more per charge but may go further, so the per-charge number alone misleads. Enter the range you actually gain from the charge, and the tool divides the cost by that range. That figure is the one to compare with petrol or diesel costs, with public charging prices, and across different home tariffs when you are choosing an energy plan.
Use this calculator before you switch tariffs or before you buy an electric car, and again after your first months of ownership with real numbers from your bills. Enter your true overnight price, your real charging losses if your charger reports them, and the range you actually get rather than the brochure figure. Keep a simple log of each charge, the kilowatt-hours drawn and the price paid, so after a month you can replace estimates with your own real average. That real average is the number to use when you compare tariffs, because brochure figures rarely match daily driving. Home charging is usually the cheapest way to run an electric car, and this tool shows by exactly how much, one charge at a time.