How the calculation works
Energy used by the car. Annual miles divided by efficiency in miles per kWh. Most EVs manage 3–4 mi/kWh across a year, less in winter and on motorways.
Energy from the grid. Some energy is lost between the meter and the battery, usually around 10% on a home wallbox. The calculator adds that to home charging. Public charger prices already include their losses.
Petrol comparison. UK mpg uses the imperial gallon, 4.546 litres:
Home charging rate makes the difference
The gap between a cheap overnight EV tariff and public rapid charging can be ten times or more per kWh. That's why the home charging share matters so much. If you charge almost entirely at home on an off-peak rate, running costs per mile are a fraction of petrol. If you rely mostly on public rapid chargers, the saving shrinks and can disappear.
Will it charge overnight?
A typical 7 kW home charger adds around 35–40 kWh in a five-and-a-half hour cheap window, which is well over 100 miles for most cars. The "average home charge per car per night" figure shows what you actually need. For most drivers it's far less, so a few hours on the cheap rate is enough.
With two EVs on one supply, plus a heat pump or battery, check the total load. Many chargers can balance load automatically to keep you under your main fuse rating.
What's not included
This compares fuel costs only. Servicing, tyres, insurance, Vehicle Excise Duty and depreciation all differ between electric and petrol cars, and company-car tax rules differ again.
Frequently asked questions
How much does it cost to charge an EV at home?
Multiply the kWh you put in by your electricity rate. On a cheap overnight EV tariff, a full charge of a typical car costs a few pounds. The calculator works out your annual cost and cost per mile.
What is a good EV efficiency in miles per kWh?
Around 3.5 mi/kWh is a reasonable year-round average for many cars. Small, efficient models can exceed 4, while large SUVs may be under 3, especially in winter.
How much energy is lost when charging an EV?
Typically around 10% on a home AC charger, more in very cold weather or at low charging currents.
Is charging an EV cheaper than petrol?
At home on an off-peak tariff, almost always by a wide margin. On public rapid chargers the cost per mile can approach or exceed an efficient petrol car.