How to Calculate EV Charging Costs Per kWh

Forget pence per mile for a second. The only number that lets you compare charging at home, at work and at a motorway rapid is cost per kWh — and the maths behind it is genuinely simple once you've seen it done. Two short formulas and one honest fudge factor, and you'll never be surprised by a charging bill again.

The core formula

Everything starts here:

Cost = energy used (kWh) × price per kWh

If you put 30 kWh into the battery at 7p per kWh, that session cost £2.10. Put the same 30 kWh in at a 79p rapid charger and it's £23.70. Same energy, wildly different bill — which is exactly why per-kWh thinking matters.

The price per kWh is the easy half; your supplier or the charge point app tells you that directly. The energy used is where people get tripped up, so let's pin it down.

Step 1: know your car's efficiency

Your efficiency is how far the car travels on one kWh. In the UK it's usually quoted as miles per kWh; on the Continent as km per kWh (or, confusingly, kWh per 100 km).

• A small, efficient EV manages 4.0–4.5 miles per kWh (around 6.5–7 km/kWh).
• A mid-size saloon sits near 3.5 miles per kWh (≈5.6 km/kWh).
• A large SUV or van in winter can drop to 2.5 miles per kWh (≈4 km/kWh).

Use your own trip-computer average, not the brochure figure — real-world efficiency is lower, especially in cold weather and at motorway speeds.

Step 2: turn distance into energy

To find the energy your driving actually needs:

Energy (kWh) = distance ÷ efficiency

Drive 800 miles in a car doing 4 miles per kWh and you need 200 kWh at the wheels.

Step 3: add charging losses (~10%)

Here's the fudge factor everyone forgets. Not all the electricity you pay for reaches the battery. Some is lost as heat in the cable, the onboard charger and the battery itself. On a home AC charger, reckon on about 10% losses — slightly more in cold weather, slightly less on a warm day.

So the energy you actually buy is:

Energy billed = energy needed ÷ 0.9

That 200 kWh at the wheels becomes roughly 222 kWh on your meter. Skip this step and you'll consistently underestimate your costs by a tenth.

Step 4: multiply by price

Now bring it together for the UK at an off-peak EV rate of 7p:

• Energy billed: 222 kWh
• Price: £0.07 per kWh
• Monthly cost: 222 × 0.07 = £15.54

At the standard 25p rate, the same month is 222 × 0.25 = £55.50. The formula doesn't change — only the price you plug in.

The same worked example by country

Let's run a driver covering the local equivalent of around 800 miles (≈1,300 km) a month, including the 10% loss:

Country	Efficiency used	Energy billed	Off-peak price	Monthly cost
United Kingdom	4.0 mi/kWh	222 kWh	7p	£15.54
Germany	6.0 km/kWh	241 kWh	22 ct	€53.02
Netherlands	6.0 km/kWh	241 kWh	24 ct	€57.84

(The Continental rows cover ~1,300 km, hence slightly more energy than the UK's 800 miles — they're not meant to match to the penny, just to show the same method.)

A quick reality check

To sanity-check any quote or app estimate, keep these rules of thumb in your head:

• Home AC losses ≈ 10%. DC rapid charging is often a little more efficient on losses but far more expensive per kWh, so the bill is still higher.
• Cold weather hurts twice — lower miles per kWh and higher charging losses.
• Heat pumps and pre-conditioning draw energy that never moves the car, so winter cost-per-mile climbs even if your driving doesn't.

Get comfortable with these four steps and you can price any charging decision in your head. And when the maths tells you a home charger pays for itself, our directory lists certified local installers who can quote you for one.