How to use the EV charging cost calculator
- Enter the electricity price per kWh from your bill or the charger, and any charging losses you know.
- For a charging session, enter the usable battery capacity and the start and end state of charge.
- For a trip, enter the distance and your car’s efficiency in whichever unit it reports. Optionally add a fuel car to compare.
- Press Calculate. Changing a unit converts the number so it still means the same thing.
Worked examples
Sample figures, not current prices. Charging a 75 kWh battery from 20% to 80% stores 45 kWh. With 10% charging losses, about 50.0 kWh comes from the supply, which at 0.30 per kWh costs 15.00.
A 300-mile trip in a car using 30 kWh/100 mi needs 90 kWh. At 0.15 per kWh with no extra losses that’s 13.50, or 0.045 per mile.
Charging losses
Energy stored in the battery is less than energy drawn from the supply. The difference depends on the charger, the charging power, the battery’s temperature and how full it is. Because it varies so much, the calculator doesn’t assume a value: enter a percentage if you know it, for example from comparing a home charger’s meter with the energy the car reports adding.
If your efficiency figure already includes charging losses, for example because you worked it out from your electricity meter, leave losses at 0 so they aren’t counted twice. A trip-computer figure usually reflects energy taken from the battery, which excludes charging losses.
Formulas used
energy stored (kWh) = battery (kWh) × (end % − start %) ÷ 100
energy from supply = energy stored ÷ (1 − losses ÷ 100)
session cost = energy from supply × price per kWh + session fee
trip energy (kWh) = distance × efficiency (kWh per distance)
cost per mile or km = trip cost ÷ distance
1 mi/kWh = 100 ÷ (kWh/100 mi) 1 Wh/km = 0.1 kWh/100 km Frequently asked questions
Why does charging cost more than the battery capacity suggests?
Some energy is lost as heat in the charger, cables and battery while charging, so the energy you pay for at the meter or charger is more than the energy stored. Losses vary with charger type, power level, temperature and battery state. Enter a loss percentage if you know it from your own meter readings or the charger’s data; leave it at 0 if your efficiency figure was already measured at the wall.
Where do I find my car’s efficiency?
The trip computer usually shows kWh/100 km, Wh/mi or mi/kWh. US window stickers list kWh/100 mi. A long-term trip-computer average reflects your own driving better than a label figure.
Does this include public charger fees?
Enter any per-session fee or connection charge in the session fee box. Some networks also charge by the minute or apply idle fees; those aren’t modelled.
Is this a full running-cost comparison with a fuel car?
No. It compares energy cost only, using the figures you enter. Purchase price, maintenance, insurance, tax and depreciation aren’t included.
What currency does it use?
Whatever you type. The currency box is only a label; there is no exchange-rate conversion and no live price data.
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