How ChargeCostFinder Calculates Your Charging Cost
Two real numbers multiplied, not a national average
Every page on this site multiplies two genuinely sourced figures: EIA Electric Power Monthly, Table 5.6.B, residential, by state (src/data/rates-by-state.csv), and EPA/DOE fueleconomy.gov bulk vehicles.csv, combined kWh/100mi (src/data/ev-models.csv). Lucid Air Pure RWD with 19 inch wheels at 23.141 kWh/100mi and Vinfast VF 8 Plus at 76.0938 kWh/100mi show how wide that spread actually is, more than 3x, which is why one national EV efficiency number would hide more than it reveals.
The gas-car comparison, and what it isn't
EIA Weekly Retail Gasoline Prices, regular grade, all formulations, US average, week of 2026-08-24. EPA Automotive Trends Report, model year 2024 — gasoline-only new-vehicle fleet average (27.2 mpg blended minus the reported 1.7 mpg BEV/PHEV lift). Both are national constants, not per-state figures, EIA does not publish a state-level retail gasoline price series, only regional (PADD) ones, so this site is honest about using one national number for the gas side rather than manufacturing a false per-state precision it can't back up.
Why charger losses aren't double-counted
EPA's kWh/100mi figure is measured "from the wall", a calibrated AC energy meter sits between the outlet and the vehicle during the dynamometer test, so charger and onboard-converter losses are already folded into the published number. Applying a separate home-charging-loss factor on top would overstate the true cost, so this model applies none.
Annual mileage and full-charge cost
fueleconomy.gov's own fuel-cost-calculator default annual-mileage assumption: 15,000 miles/year. The full-charge figure on each page is the EPA's own combined range multiplied by the EPA's own consumption rate, the energy actually used in the EPA test, not the battery pack's nameplate capacity, which isn't in this dataset.
See the method applied
Three worked examples, each multiplying a real EIA rate by a real EPA figure: Lucid Air Pure RWD with 19 inch wheels in North Dakota, Vinfast VF 8 Plus in Hawaii, and Vinfast VF 8 Plus in North Dakota. For why the state side of that math swings so much, see the guide to state rate differences; for cases where the result favors gas, see the guide to when charging costs more.