Understand your estimate

How to use this result

Home charging cost is the energy drawn from the wall multiplied by your price. The wall energy is the energy the battery needs divided by one minus the charging loss, so losses raise the bill beyond what the car’s display shows.

Method reviewed · Calculation methods · Evidence and source policy

Find the right inputs

Distance driven and car consumption

Distance per week; kWh per 100 miles or km

Use the car’s trip-computer average or documented figure in the same unit as the distance.

Charging loss

Percent of wall energy

Use a measured loss from a wall meter against the car’s charge count, or state your assumption.

Your electricity price

GBP, USD or EUR per kWh

Enter major currency units; 28 pence means 0.28. An optional second price covers off-peak charging.

The calculation

Battery kWh per week = distance × consumption ÷ 100. Wall kWh = battery kWh ÷ (1 − loss). Cost = wall kWh × average price × weeks. Cost per 100 miles = weekly cost ÷ weekly distance × 100.

A worked arithmetic example

Illustrative arithmetic: 200 miles a week at 30 kWh per 100 miles needs 60 kWh in the battery. With 10% charging loss that is about 66.7 kWh from the wall, or $13.33 a week at $0.20/kWh, about $693 over 52 weeks and $6.67 per 100 miles. These values are assumptions, not a typical car.

What the estimate can tell you

The result covers home charging only. If part of your charging is at a cheaper off-peak price, enter that share and price to see the saving; do not assume all charging can move to the cheap window. Compare cost per 100 miles only between cars measured the same way.

Questions about this calculation

Why is the wall energy higher than the battery energy?

Some energy is lost as heat in the charger, cable and battery while charging. The loss varies with charger, temperature and charging power, so use a measured figure where you can.

Should I use the car’s displayed kWh per 100 miles?

Use it for the battery-side consumption, and then add the charging loss separately. If your figure already comes from wall-meter readings, enter 0 for loss to avoid counting losses twice.