What this calculator works out
This calculator costs a charging session from the energy added and your electricity price, estimates the range that energy provides, and gives a cost per mile.
Cost per mile is the figure that allows comparison with petrol or diesel — and the gap between home charging and public rapid charging is larger than most people expect.
Enter your details
Default unit rates are the Ofgem price cap average for Great Britain, Direct Debit, 1 July to 30 September 2026, including VAT. The cap is reviewed quarterly — use the rate from your own bill where it differs.
Before you calculate
- Use the price for the charger you are using. Home overnight rates on an EV tariff can be under 10p per kWh; public rapid charging is frequently 70p to 85p.
- Efficiency in miles per kWh varies with speed, temperature and driving style — typically 2.5 to 4.5 for most cars, and worse in winter.
- Charging losses mean the energy drawn from the supply exceeds the energy stored, typically by 10 to 15%. Home charging is billed on what is drawn.
- Battery capacity added is what the session delivered, not the battery's total size.
At 8p per kWh on an overnight tariff, a car doing 3.5 miles per kWh costs 2.3p a mile. At 79p on a public rapid charger, the same car costs 22.6p a mile — nearly ten times as much, and more than a petrol car managing 45 mpg. The economics of an EV depend heavily on where it charges.
How this calculator works
Energy times price, energy times efficiency:
Cost = kWh added × price in pence ÷ 100
Range added = kWh added × miles per kWh
Cost per mile = cost ÷ range added × 100The calculation uses the energy delivered to the battery. Home electricity is metered at the supply, so the amount billed is higher by the charging losses — typically 10 to 15% — which makes the real home cost per mile slightly above the figure shown.
Worked example: a 50 kWh charge
Using the default figures — 50 kWh added at 26.11p per kWh, at 3.5 miles per kWh:
- Charge cost: £13.05
- Range added: 175 miles
- Cost per mile: 7.5p
For comparison, a petrol car at 45 mpg with fuel at £1.45 a litre costs 14.7p a mile — more than twice as much. Move that same charge to a public rapid charger at 79p per kWh and it becomes 22.6p a mile, which is more expensive than the petrol car. The technology has not changed; only where it was plugged in.
Common mistakes
- Using a home rate to judge a car that charges publicly. The difference is severalfold.
- Ignoring charging losses. The meter records more than the battery receives.
- Using summer efficiency year-round. Cold weather reduces range substantially.
- Assuming rapid charging is always available at the quoted rate. Charging slows markedly above about 80% state of charge.
- Comparing against official petrol economy. Use an observed figure for both.
Frequently asked questions
How much does home charging cost?
It depends entirely on the tariff. On a standard rate it is broadly the same as any other electricity use. Dedicated EV tariffs offer a low overnight rate — often a fraction of the day rate — in exchange for charging in a defined window. For anyone with off-street parking, that tariff is usually the single largest factor in an EV's running cost.
Why is public charging so much more expensive?
Rapid chargers carry substantial installation and grid connection costs, occupy commercial land, and include VAT at 20% rather than the 5% applied to domestic electricity. The result is a price several times the domestic rate. For drivers without off-street parking, this is the central financial question about EV ownership.
How does cold weather affect range?
Considerably — commonly 20 to 30% in freezing conditions, from battery chemistry, cabin heating and denser air. Preconditioning the car while still plugged in uses grid electricity rather than battery, which recovers much of the heating penalty. Heat pumps, fitted to many newer models, reduce it further.
Should I charge to 100%?
For most lithium batteries, routinely charging to 100% and sitting at that state accelerates degradation, and manufacturers commonly recommend an 80 to 90% daily limit with full charges before long journeys. Rapid charging also slows sharply above 80%, so on a long trip several shorter stops are usually faster than one long one.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — electric vehicle grants, charge point regulations and energy pricing
- MoneyHelper — comparing the running costs of electric and petrol cars
Sources are checked at publication and can change — how I choose and check references.