What charging an EV at home costs

Efficiency times distance times price: that is the entire calculation, and it fits on one line. What makes home charging confusing is not the math but the three inputs, each of which hides a small complication. The calculator below does the arithmetic; the steps beside it show exactly what it is doing, so you can check it with a pencil.

The figures already filled in are an illustrative example, not a typical car or a typical electricity rate. Replace them with your own.

Your numbers

Efficiency (kWh per 100 miles) From the car's efficiency label or its trip computer. Miles per month Only the miles charged at home. Electricity price ($ per kWh) Your all-in price per kWh, from your bill. Charging overhead (%) A placeholder for energy lost between the outlet and the battery. Set to 0 to ignore.

$52.80

per month · $633.60 per year · 5.3¢ per mile

The formula, one step at a time

1. Turn the efficiency figure into kWh per mile. 30 kWh ÷ 100 mi = 0.3 kWh per mile Labels quote energy per 100 miles, the way fuel is quoted per gallon. Dividing by 100 gives the energy one mile uses. Lower is better.
2. Multiply by the month's miles. 0.3 × 1,000 mi = 300 kWh into the battery This is the energy the car needs to cover the distance.
3. Allow for charging overhead. 300 × (1 + 10%) = 330 kWh from the wall The meter counts what leaves the outlet, and a share of that becomes heat along the way. How large a share varies with the equipment, the charging speed and the weather; the 10% here is a round placeholder, not a measurement.
4. Price it. 330 kWh × $0.16 = $52.80 That is the monthly cost. Twelve of them make the yearly figure.
5. Divide back down to a per-mile cost. $52.80 ÷ 1,000 mi = 5.3¢ per mile The per-mile figure is the one to compare with anything else you drive.

Worked example: 30 kWh/100 mi, 1,000 miles, $0.16 per kWh, 10% overhead. Illustrative inputs only.

Where each number actually comes from

Efficiency. The official figure for an electric model is published on its window label and at fueleconomy.gov, in kWh per 100 miles. It is a standardized result. Your own figure will wander with speed, temperature and terrain; many cars show a running average on the dash, and that number, taken over a few weeks, is better than the label for your purposes. Expect it to shift between seasons. Cold weather in particular tends to raise consumption, partly from heating the cabin and partly from the battery itself.

Price per kWh. This is the input most people get wrong. An electric bill usually splits into a supply or generation charge and a delivery charge, and both are billed per kWh. The number you want is the two added together, plus any per-kWh taxes and riders, divided out to a single rate. The simplest honest method: take a recent bill, subtract the fixed monthly customer charge (you pay that whether or not you own an EV), and divide what is left by the kWh used.

Two structures complicate this. With tiered pricing, the price rises once your monthly use crosses a threshold, and the EV's energy lands in the most expensive tier because it is added on top of everything else. With time-of-use pricing, the rate depends on the hour, and overnight charging may sit at a different rate from the evening peak. In both cases, use the rate that will actually apply to the car's kWh, not the average across your bill. Your utility's rate schedule, usually posted on its website, lists which plans exist; what is available varies by utility.

Overhead. Energy is lost converting household current into what the battery stores. The loss is real but not a fixed percentage — equipment and conditions change it. If your car or charger reports energy delivered, and your utility or a smart plug reports energy drawn, the difference between the two over a month is your own overhead figure, and it is better than any placeholder.

What the calculator deliberately ignores

It prices only energy charged at home. Public fast charging is sold on different terms — per kWh in some places, per minute in others, sometimes with a session fee or a membership — and the per-mile cost can land far from the home figure in either direction. If a real share of your miles are charged away from home, run those miles separately at the price you actually pay there.

It also leaves out equipment. A dedicated home charger and any electrical work to support it are a one-time cost, and the fairest way to include them is to spread them over the miles or months you expect to use them — the same approach as treating tires as a line item. Some households manage with an ordinary outlet and slower charging; whether that works depends on how far you drive between nights at home.

And it does not compare anything. To set the result next to a gasoline car, convert both to cents per mile. A car doing 25 mpg on $3.50 gas spends 14¢ a mile on fuel; the sensitivity grid in what a gas price change does to your month shows how that figure moves. Whether an electric car comes out ahead for you depends on your rate, your efficiency and your mix of home and public charging — which is exactly why the inputs above are yours to change.

One small check before trusting any result: multiply your monthly kWh from step three by twelve and look at a year of your electric bills. If the car's energy would be a large share of what the house already uses, ask your utility whether the added use pushes you into a different tier or makes a different plan cheaper.