This calculator estimates what a single home-charging session costs: enter your battery size, the state of charge you are starting from and charging to, and a charging efficiency, and it converts that into kilowatt-hours drawn from the wall and the dollar cost at the current residential electricity price.
This calculator uses local defaults synced from public energy and vehicle datasets. It is designed to keep working without a live browser-side API call, so the page remains usable even when an upstream provider is temporarily unavailable. The formulas are intentionally transparent: electricity cost equals energy consumed multiplied by the EIA residential electricity price, while gasoline cost equals miles driven divided by miles per gallon and multiplied by the EIA regular gasoline price. The numbers are estimates, not promises, because driving speed, weather, tire condition, charger losses, local taxes, and utility plans can change real costs.
For EV comparisons, EPA energy consumption is normally expressed as kWh per distance or MPGe, and EIA prices are published by period. EVCar stores the latest synced period in the database and displays the calculation result from those stored values rather than asking the visitor browser to call EIA directly. That design makes the tool easier to audit and avoids a broken user experience if an API key is missing or a data source is slow. When state-level electricity data is available, the state value should be preferred; otherwise the national residential default is a reasonable fallback for a quick estimate.
The main limitation is that fuel cost is only one part of ownership. Insurance, depreciation, maintenance, tire wear, registration fees, incentives, financing, charger installation, and public fast-charging premiums are not included unless explicitly shown. Users comparing a specific EV with a specific gasoline vehicle should treat the result as a directional estimate and then adjust inputs for their real annual mileage, charging mix, local utility rate, gasoline price, and vehicle efficiency. Estimates based on EIA/EPA data, actual costs vary.