How much a charge costs
The cost of charging an electric car depends on three things: how much energy goes into the battery, how much is lost on the way, and what you pay per kilowatt-hour.
- Energy added = usable battery capacity × (charge level after − charge level before)
- Energy drawn from the grid = energy added ÷ charging efficiency
- Cost of the charge = energy drawn × electricity price
Charging is never 100% efficient. The onboard charger, the cables and battery heating or cooling waste some power, usually 5 to 15% on a Level 2 wall charger and more on a standard 120 V outlet.
Worked example
A car with a 75 kWh usable battery charges from 20% to 80% at home, at 17 cents per kWh, with 90% efficiency.
- Energy added: 75 × 60% = 45 kWh.
- Energy drawn from the grid: 45 ÷ 0.90 = 50 kWh.
- Cost of the charge: 50 × $0.17 = $8.50.
- At 30 kWh per 100 miles, that charge adds about 150 miles of range.
Cost per mile compared with gas
The calculator also compares the running cost per 100 miles. At 30 kWh per 100 miles, an EV costs 30 ÷ 0.9 × $0.17 = $5.67 per 100 miles. A 30 mpg gas car at $3.20 a gallon costs 100 ÷ 30 × 3.20 = $10.67. Over 12,000 miles a year, the EV saves about $600 and costs about $680 a year to charge.
What changes the result
| Factor | Typical range | Effect |
|---|---|---|
| Home electricity rate | 10 to 40 cents per kWh | The biggest driver of cost |
| Off-peak EV rate | 5 to 15 cents per kWh | Can halve the cost of charging |
| DC fast charging | 40 to 60 cents per kWh | Often close to the cost of gas |
| Winter driving | +15 to 35% energy use | Cabin and battery heating |
| Highway speed | +10 to 25% energy use | Air drag rises quickly with speed |
Tips to charge for less
- Use time-of-use rates. Many utilities offer cheaper night rates for EV owners; schedule charging in the car’s app.
- Install a Level 2 charger. It is faster and wastes less energy than a standard outlet.
- Precondition while plugged in. Heating or cooling the cabin from the grid saves battery energy on the road.
- Keep fast charging for trips. Daily DC fast charging costs more and can age the battery faster.
The energy use on the car’s EPA label (in kWh per 100 miles) is the best starting point. Your real figure appears in the trip computer after a few weeks of driving.