EV vs Petrol Running Costs UK 2026: Worked Savings

Use comparable energy measurements

For petrol or diesel, UK miles per gallon means an imperial gallon, approximately 4.54609 litres. Annual litres equal annual miles divided by mpg, multiplied by 4.54609. Multiply litres by the price per litre to obtain fuel expenditure. Do not use a US-gallon mpg figure in this formula.

For the EV example, assume 3.5 miles per kWh measured at the battery and 90% charging efficiency. Annual electricity purchased equals miles divided by 3.5, then divided by 0.90. If your efficiency figure already includes charging losses at the meter, do not apply those losses a second time. Use matching measurement boundaries for a useful comparison.

Work through petrol and diesel baselines

Assume 10,000 annual miles, petrol consumption of 45 imperial mpg and a petrol price of £1.45 per litre. The calculation is 10,000 ÷ 45 × 4.54609 × £1.45, or approximately £1,465 a year. This is the energy bill only, not the complete cost of owning that car.

For a separate diesel example, assume 55 imperial mpg and £1.50 per litre. The same mileage gives approximately £1,240. Neither efficiency is an industry average or a matched vehicle test. Replace them with your own records over representative journeys. Comparing a large petrol SUV with a small electric hatchback answers a different question from comparing similar-sized vehicles.

Calculate three EV charging scenarios

At the stated efficiency assumptions, 10,000 miles requires approximately 3,175kWh purchased. At an illustrative 25p/kWh, that costs £794 annually. Against the petrol example, the energy saving is about £671; against the diesel example, about £446. The rounding is to whole pounds.

At 10p/kWh, the same electricity costs £317. At 70p/kWh, it costs £2,222. The latter is approximately £757 more than the petrol baseline. These prices represent sensitivity scenarios, not available offers. They show why a driver relying on expensive public charging cannot assume the saving available to a household charging overnight at home.

Mix charging locations and compare the household bill

Suppose 80% of purchased energy is at 10p/kWh and 20% at 70p/kWh. The weighted unit price is 22p/kWh, giving approximately £698 a year. This weighting is by energy, not by the number of sessions: one large public charge can outweigh several small home top-ups.

Use our off-peak charging guide and tariff comparison tool to examine the rest of the house. A lower EV rate can come with different daytime prices or standing charges. Count an existing standing charge once; when comparing two contracts, include the difference. Add public subscriptions, parking or overstay fees separately where they apply to your routine.

Work out the break-even electricity price

The petrol baseline costs about 14.65p per mile. Multiply that by 3.5 miles/kWh and by 0.90 charging efficiency: the break-even purchased electricity price is approximately 46.1p/kWh. Below that, this EV example has a lower energy cost; above it, the petrol example does. It remains an energy-only comparison.

For the diesel assumptions, the corresponding threshold is approximately 39.1p/kWh. Repeat the calculation if winter efficiency falls, motorway mileage rises or your charging mix changes. A useful test is to calculate an ordinary month and a difficult month. The result should support a realistic annual budget, not require every week to achieve the most optimistic case.

Add purchase price, tax and depreciation

A hypothetical £4,000 extra upfront outlay divided by the £671 annual petrol energy saving suggests roughly six years to recover that difference through energy alone. This simple payback excludes depreciation, interest, insurance, repairs and resale value. It is not a total cost of ownership forecast, and may change substantially with those items.

EVs are not universally exempt from vehicle tax: consult DVLA: vehicle tax rate tables and our UK EV tax guide. Check purchase support in the Electric Car Grant guide, using the final quoted price without deducting an included grant twice. For a purchase comparison, use purchase price minus expected resale value plus operating costs; for a lease, use payments and charges. Avoid adding both full purchase cost and depreciation as separate expenses.

References: DVLA: vehicle tax rate tables