EV charging cost depends on the energy drawn from the grid, not only the battery percentage shown on the dashboard. The usable battery increase must be adjusted for charging losses before it is multiplied by the electricity rate.
The charging-cost formula
Charging cost = battery capacity × charge added ÷ charging efficiency × electricity rate. Enter charge added and efficiency as percentages, then convert them to decimals in the calculation. A home charger may draw more energy than the battery stores because wiring, conversion, and thermal systems consume some electricity.
Worked example: 75 kWh battery
For a 75 kWh battery charged from 20% to 80%, the added energy is 75 × 0.60 = 45 kWh. At 90% efficiency, grid energy is 45 ÷ 0.90 = 50 kWh. At $0.16 per kWh, the session costs 50 × $0.16 = $8.00.
Home, public, and time-of-use rates
Use the energy rate that actually applies to the session. A public charger may price by kWh, time, session, or a combination. A home bill may have tiers, fixed charges, or off-peak rates. Run separate scenarios instead of blending rates into one false average.
What the estimate does not decide
This is an energy-cost estimate, not a complete ownership-cost calculation. It does not include charger installation, subscription fees, parking, demand charges, or battery degradation. Compare the result with charging time and road-trip tools when planning a routine.
Sources
The figures and rules in this guide are checked against:
- Charging Electric Vehicles at Home — U.S. DOE Alternative Fuels Data Center
- Electric Power Monthly: Average Price of Electricity to Ultimate Customers — U.S. Energy Information Administration
- Vehicle Cost Calculator — U.S. DOE Alternative Fuels Data Center
- Home Charging — Tesla Support