What the inputs mean
- Distance per year: your own yearly mileage. The odometer change over a year, or your service records, give a real figure.
- Fuel economy and fuel price: the gas car's mpg (or L/100 km in metric) and what you pay per gallon or liter.
- EV efficiency: energy per distance, in kWh per 100 miles, miles per kWh, or the metric versions. Lower kWh/100 mi means a more efficient car.
- Electricity price: what you pay per kWh. At home, it is on your power bill; public fast charging often costs more per kWh than home charging.
- Charging loss: an assumption, default 10%. Some energy turns to heat between the outlet and the battery. If your efficiency figure comes from a car's trip display, it usually counts battery energy, so keep a loss. EPA window-sticker figures already count wall energy, so set the loss to 0 with those.
The formulas
gas cost per year = miles ÷ mpg × price per gallonEV cost per mile = kWh per 100 mi ÷ 100 × price per kWh ÷ (1 − charging loss)The EV yearly cost is the cost per mile times the miles.
Worked example
12,000 miles a year. The gas car gets 28 mpg with fuel at 3.50 per gallon: 12,000 ÷ 28 = 428.6 gallons, 1,500.00 a year, 0.125 per mile. The electric car uses 30 kWh per 100 miles, electricity costs 0.16 per kWh, and the charging loss is 10%: 0.30 × 0.16 ÷ 0.90 = 0.0533 per mile, 640.00 a year, drawing 4,000 kWh from the grid. The difference is 860.00 a year in favour of the electric car with these prices. With the loss set to 0, the EV cost is 576.00.
In metric: 20,000 km, 7 L/100 km at 1.80 per liter is 2,520.00. An EV using 18 kWh/100 km at 0.30 per kWh with 10% loss is 0.06 per km, 1,200.00 a year.
What this leaves out
This compares energy costs only. It does not include the purchase price, insurance, maintenance, tax credits or subscription charging plans, and it uses one price for the whole year. Winter, highway speed and heavy loads raise energy use in both kinds of car. Run it with your own numbers and, for a range, a second time with worse efficiency figures.
Questions
How much does it cost to charge an electric car per mile?
Divide the kWh per 100 miles by 100, multiply by your price per kWh and divide by 1 minus the charging loss. 30 kWh/100 mi at 0.16 per kWh with a 10% loss is 0.0533 per mile.
How much can I save with an electric car?
It depends on your mileage and prices. With 12,000 miles a year, a 28 mpg gas car at 3.50 per gallon costs 1,500.00, and an EV at 30 kWh/100 mi and 0.16 per kWh with 10% charging loss costs 640.00: a difference of 860.00 a year.
How do I calculate EV charging cost for a year?
Multiply your yearly miles by the cost per mile. 12,000 miles at 0.0533 per mile is 640.00, or about 4,000 kWh drawn from the grid at 0.16 per kWh.
Do I need to add charging losses?
Only if your efficiency figure is battery energy, as trip displays usually show. EPA window-sticker figures already include charging losses, so set the loss to 0 when you use them.