Calculate electric car charging costs using energy from the supply · United Kingdom

Estimate energy added to the battery

Use the battery's usable capacity when available. Charging an illustrative 60 kWh usable battery from 20% to 80% adds approximately 36 kWh: 60 × (80 − 20) ÷ 100. Displayed percentage and usable capacity can vary with vehicle management and battery condition. The advertised gross capacity may include an inaccessible buffer.

Allow for charging losses once

If losses are defined as 10% of energy drawn from the supply, 36 kWh stored requires 36 ÷ 0.9 = 40 kWh from the supply. Multiplying by 1.1 would describe a different assumption. Use your measured charging energy where possible. Do not add losses again if the consumption figure already includes them.

Use the price for that charging session

Multiply billable kWh by the applicable charging price. Public charging may also involve session, time, parking or subscription fees; keep those separate. At home, a time-of-use tariff requires the rate for the actual charging hours. Compare several real sessions rather than assuming a home tariff applies to every journey.

Compare distance on the same basis

For an illustrative supply consumption of 18 kWh per 100 km, travelling 1,000 km requires 180 kWh. Fuel energy cost uses litres per 100 km multiplied by distance and price per litre. Keep distance units consistent and distinguish measured supply consumption from an in-car display. Weather, speed, heating, cooling and route can affect energy use.

Separate energy savings from ownership costs

A fuel comparison estimates energy costs only. Purchase price, servicing, insurance, taxes and depreciation need separate entries for a total ownership comparison. Monthly projections assume the stated mileage repeats; annual mileage is usually a stronger planning input. Charging equipment and electrical installation choices should follow vehicle guidance and an assessment by a qualified installer.

Data sources

Last reviewed: 2026-09-08