EV vs gas cost — methodology

What this calculator does

It compares the cost to run an electric car against a gasoline car over a period you choose, and — if you supply purchase prices — works out when the EV repays any higher upfront cost. It also estimates the CO₂ you avoid each year.

The formulas

Annual energy and fuel

ev_energy_at_wheels = annual_miles / ev_miles_per_kwh
ev_energy_from_wall = ev_energy_at_wheels / charge_efficiency
gas_gallons         = annual_miles / gas_mpg

We bill the EV on energy drawn from the wall, because that is what your meter records and what you pay for.

Annual cost and saving

ev_annual_fuel  = ev_energy_from_wall * electricity_price_per_kwh
gas_annual_fuel = gas_gallons * gas_price_per_gallon
annual_saving   = gas_annual_fuel - ev_annual_fuel
cost_per_mile   = annual_fuel_cost / annual_miles      (each vehicle)

Break-even (only when purchase prices are entered)

upfront_difference = ev_purchase_price - gas_purchase_price
breakeven_years    = upfront_difference / annual_saving

We guard the division: if the EV is the same price or cheaper upfront it leads from year one; if it costs more to buy and more to run, it never breaks even on fuel and we report that honestly rather than showing a misleading number.

Emissions

co2_gas   = gas_gallons * gasoline_co2_per_gallon
co2_ev    = ev_energy_from_wall * grid_co2_per_kwh
co2_saved = co2_gas - co2_ev

Default values

Every default below is editable in the calculator and shown with its source in the calculator’s assumptions table. The two prices are the most time-sensitive — always replace them with your own.

How we keep it honest

The calculation logic lives in a small, pure function that is unit-tested against normal, edge and invalid inputs (for example, a zero fuel economy returns “no result” rather than infinity). If you spot an error, tell us and we’ll fix it.