What it costs to charge an electric car at home

Most pages answering this question give you a national average electricity price and multiply it out. That produces a number that is wrong for almost everybody, because residential electricity rates vary by a factor of three or more across the country and by time of day within a single household.

So here is the formula instead. Get your rate off your own bill and the answer takes thirty seconds.

Where to find your two numbers

1. 1.Your electricity rate. On your bill, look for a per-kWh figure. Include delivery and supply charges if they are separate -- the total per-kWh cost is what you actually pay. If you are on a time-of-use plan, note the off-peak rate as well, because that is when you will charge.
2. 2.Your car's efficiency. In the car's trip computer, usually shown as mi/kWh or as kWh/100 mi. Use your own long-term average rather than the EPA figure; the EPA number is a test result, yours is your driving.

A worked example

Substitute your own two numbers. If your off-peak rate is $0.10 and your peak is $0.32, the same 1,000 miles is either $29 or $91 -- which is why scheduling matters more than almost anything else you can control.

Efficiency losses: the part people forget

Not every kilowatt-hour that leaves your wall reaches the battery. Some becomes heat in the cable and the car's onboard charger. That means your meter will show slightly more energy than the car reports receiving -- so a cost calculated from the car's own consumption figure is a slight underestimate of what you paid.

We are not going to print a loss percentage we cannot source for your specific car. The practical guidance: if you want the exact figure, read it from a charger that meters at the wall, or from your utility's usage data on a night you charged and nothing else unusual ran.

How to spend less

• Charge off-peak. If your utility offers a time-of-use plan, this is by far the biggest lever. Your car can almost certainly schedule it; if not, a smart charger can.
• Check for an EV-specific rate. Many utilities offer one. It is a phone call.
• Do not charge to 100% routinely unless your car's manual recommends it. Most manufacturers suggest a daily ceiling below full, and the last stretch is also the slowest.
• Precondition while plugged in. Heating or cooling the cabin from wall power rather than the battery costs the same energy but does not eat your range.

Work out your own numbers

The charging speed calculator shows how long a charge takes and how much energy it moves, which is the input to all of the above. For the up-front side of the ledger, what installation costs.