About the EV Charging Cost Calculator
One of the biggest attractions of an electric car is how little it costs to run, but working out exactly how little is harder than with a petrol car. There is no price per gallon on a sign; instead there is a battery measured in kilowatt-hours, a charge level shown as a percentage, an electricity tariff, and some energy lost along the way as heat. Charging at home overnight, at work, at a supermarket or at a motorway rapid charger can cost very different amounts for the same miles.
This EV charging cost calculator brings it together. Enter the battery capacity, the charge level now and the level you want to charge to, the electricity price, the charging efficiency and your car's efficiency in miles per kWh or kWh per 100 km. It gives the cost of the charge, the energy drawn from the grid, the range added, the cost per 100 miles or km, the charging time at your charger's power, and a comparison with a petrol car covering the same distance.
How to Use the EV Charging Cost Calculator
Choose whether to work in miles or kilometres.
Enter the usable battery capacity in kWh. It is in the car's specifications, and is usually a little less than the headline figure.
Enter the charge level now and the level to charge to.
Enter your electricity price per kWh and the charging efficiency — about 90 percent for a home charger.
Enter the car's efficiency: miles per kWh, or kWh per 100 km. The car's trip computer shows it.
Optionally, enter the charger power in kW, and a petrol car's fuel economy and fuel price to compare.
How the Charging Cost Is Worked Out
energy into battery = capacity × (charge to − charge now)
energy from grid = energy into battery ÷ efficiency
cost = energy from grid × price per kWh
range added = energy into battery × miles per kWh
(or ÷ kWh per 100 km × 100)
charging time = energy from grid ÷ charger powerStep-by-Step Example
A 75 kWh battery from 20% to 80%, electricity at 0.15 per kWh, 90% efficiency, 3.5 miles per kWh, a 7 kW home charger.
Into battery: 75 × (80% − 20%) = 45 kWh
From grid: 45 ÷ 90% = 50 kWh
Cost: 50 × 0.15 = 7.50
Range: 45 × 3.5 = about 158 miles
Per 100 miles: 7.50 ÷ 157.5 × 100 = 4.76
Time: 50 ÷ 7 = about 7 h 9 min
Petrol: 157.5 ÷ 30 mpg × 3.50 = 18.38, so 10.88 moreWhere You Charge Matters Most
Home charging is usually the cheapest, especially on an off-peak or EV tariff that offers low prices overnight. Many drivers do almost all their charging this way, plugging in at night like a phone.
Workplace and destination charging is sometimes free or low-cost, and is a useful top-up during the day.
Public rapid chargers are fast but often charge several times the home price per kWh. For long journeys they are essential, but a car charged mostly at rapid chargers may cost nearly as much per mile as an efficient petrol car. Try the calculator with your local rapid charger price to see the difference.
Charging Efficiency and Losses
Not all the electricity you pay for reaches the battery. Some is lost as heat in the charger, the car's onboard converter and the battery itself, and some runs the car's systems, such as battery heating, while it charges. Losses are typically around 10 percent on a home wallbox, and can be higher on a slow three-pin plug or in cold weather. DC rapid chargers skip the car's onboard converter but still lose some energy, usually billed on the energy delivered.
Charging Speed
Charging time depends on the charger's power, the car's maximum charging rate and the battery's state of charge. A standard home socket delivers about 2.3 kW, a home wallbox 7 kW, and public chargers from 7 kW up to 150 kW or more. Charging is fastest when the battery is low and slows down sharply above about 80 percent to protect the cells, which is why rapid chargers are usually quoted "to 80%". The calculator divides energy by power, so treat it as a best case for the part of the charge above 80 percent.
Real-World Efficiency
An electric car's efficiency varies more with conditions than a petrol car's. Motorway speeds, cold weather and heating the cabin can cut efficiency by 20 to 30 percent in winter, while gentle town driving in mild weather can beat the official figure. Regenerative braking recovers energy in stop-start traffic. Use the figure your car's trip computer shows over the last few weeks for the most accurate estimate.
Understanding Your Result
Charging cost is the cost of this charge.
Energy shows the energy stored in the battery and drawn from the grid.
Range added estimates the extra range from this charge.
Cost per distance gives the cost per 100 miles or 100 km.
Charging time estimates how long the charge takes at your charger's power.
Compared with petrol shows what the same distance would cost in fuel.
Worth knowing explains why most drivers charge to about 80 percent.
When Should You Use This Calculator?
Deciding whether an EV would save you money.
Comparing tariffs, home charging and public chargers.
Planning a long trip with rapid charging stops.
Working out business mileage costs for an electric car.
Checking an electricity bill after installing a wallbox.
Common Mistakes
Using the gross battery size instead of the usable capacity.
Forgetting charging losses.
Assuming full speed all the way to 100 percent.
Using a summer efficiency figure for winter driving.
Comparing with petrol using rapid charger prices only.