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How these charging costs are calculated

Two public datasets and one multiplication. Both inputs are named on every page, and the calculator lets you replace either of them.

Where the numbers come from

Vehicle consumption comes from the U.S. EPA and Department of Energy's fueleconomy.gov database — the same figures printed on the window sticker. A U.S. government work, in the public domain. This site uses the combined kWh-per-100-miles rating and the combined range rating, averaged across the trims of each model's most recent year. The current catalog covers 70 models from model years 2025-2027.

Electricity prices come from EIA's Electric Power Monthly, Table 5.6.A: average residential price per kilowatt-hour by state, for June 2026. Also public domain. These are averages of revenue divided by sales, so fixed charges and taxes are already blended in.

The formula

cost per mile = kWh per 100 miles ÷ 100 × (cents per kWh ÷ 100)

That is the whole thing. The subtlety is that EPA measures consumption at the wall, not at the battery. Charging losses are already inside the EPA figure, which is why this site never adds a separate loss factor on top — doing so would double-count them.

The same property is why the "full charge" figure here runs 10–15% above the pack's usable capacity. It is the energy your meter records to fill the battery, not the size of the battery, and it is the number that determines what you pay.

Stated assumptions

Unless you change them in the calculator: 12,000 miles a year, home Level 2 charging, gasoline at $3.50 a gallon in a 30 MPG car. The gasoline price is a stated assumption, not a live feed; local prices vary widely and the calculator takes yours.

The same data, as an API

Everything on this site is computed from public datasets and a published formula, so there is no reason to keep the result to ourselves. The figures are available as JSON at api.wattfigure.com — state rates, the appliance catalog, the vehicle catalog, and the cost calculations themselves, with an OpenAPI description and no signup for ordinary use.

It returns the same numbers this page does, because it runs the same arithmetic on the same data.

What this does not cover

Public DC fast charging, which is typically several times more expensive per kilowatt-hour. Time-of-use and dedicated EV rate plans, which in high-rate states can cost less than half the state average. Cold-weather efficiency losses, which are real and can reach a third. Demand charges, insurance, maintenance, depreciation and purchase incentives — all of which can be larger than the fuel difference.

Treat these figures as a well-sourced estimate for comparison, not as a bill.