Donaldson R F EV Charging Cost & Time Calculator
Estimate the cost and time to charge an electric car, from its battery size, current and target charge, your charger's power and your electricity tariff.
The £0.27/kWh price is just a placeholder — enter your own home or public tariff, which can vary a great deal (overnight home rates are often much cheaper than public rapid chargers).
How it is worked out
Energy added to the battery = capacity × (target % − current %) ÷ 100. Charging always loses some energy as heat, so the energy actually drawn from the wall (and what you pay for) is higher: energy from the wall = energy added ÷ efficiency. Cost = energy from the wall × your price per kWh. Charging time = energy from the wall ÷ charger power — a rough estimate, since real charging slows down as a battery fills up (especially on fast DC chargers), which this simple model doesn't capture.
Typical efficiency is often quoted around 85–95% for home AC charging; it can be lower on rapid DC chargers because more energy is lost as heat at higher power.
Source: standard energy/cost/time relationships for battery charging (capacity × percentage, energy ÷ power = time).
Comparing running costs against petrol instead? See the Fuel Economy Converter.