The formula
Battery energy = capacity × (target − starting charge) ÷ 100. Grid energy = battery energy ÷ efficiency. Cost = grid energy × tariff.
A worked example
For a 60 kWh battery charging from 20% to 80%, 36 kWh reaches the battery. At 90% efficiency, 40 kWh is billed; at 0.25 per kWh the cost is 10.00.
What this estimate includes
Capacity must be usable capacity, not gross capacity. Efficiency is an assumption, not a measured value for your vehicle. Public charging may include session, parking or time-based fees.
Common questions
Why is grid energy higher than battery energy?
Some energy is used by conversion, cooling and other charging overheads. Efficiency represents the fraction of grid energy stored in the battery.
Does choosing a currency set local electricity prices?
No. Enter the tariff you actually pay. No live price feed or automatic currency conversion is used.
Further reading
US Department of Energy: charging at home. Background reference; these tools are independent and are not endorsed by the source organization.