Petrol, Diesel or Electric: How Much Does 100 Miles Cost?

For drivers comparing petrol, diesel and electric cars, the monthly payment is only part of the calculation. The cost of covering your everyday mileage can also make a substantial difference to your budget.

Home charging can give electric vehicles a significant advantage on energy costs. However, the size of that advantage depends on your electricity tariff, the vehicle’s efficiency and how often you need to charge elsewhere.

Here’s an illustrative comparison using fuel prices and home electricity rates checked on 14 October 2026.

Comparing the cost of 100 miles

The examples below use UK average petrol and diesel prices for 12 October 2026, alongside Ofgem’s average standard variable electricity rate for Great Britain and an example dedicated EV charging tariff.

These are illustrative passenger-car examples. The efficiency figures are assumptions rather than national averages, and individual vehicles will produce different results.

The standard electricity figure is Ofgem’s October–December 2026 average for Direct Debit customers in England, Scotland and Wales. The smart charging example uses the advertised Intelligent Octopus Go rate, subject to eligibility, compatible equipment and tariff terms.

What could this mean over a year?

If the same prices and efficiency figures applied across 10,000 miles, the approximate annual energy costs would be:

• Petrol: £1,992
• Diesel: £1,819
• EV charged at home on standard electricity: £836
• EV charged at home on the example smart tariff: £241

In this scenario, charging an EV at home on standard electricity would save approximately £1,156 in energy costs compared with the petrol example, or £983 compared with diesel.

Using the example smart charging rate would increase those potential savings to approximately £1,751 against petrol and £1,578 against diesel.

These calculations assume all EV charging takes place at the stated home rate. They are illustrations using current prices, rather than forecasts of annual spending.

Why your electricity tariff matters

Having access to home charging is one part of the equation. The price you pay for that electricity is another.

Some EV tariffs offer cheaper electricity during designated overnight periods or supplier-managed charging sessions. Drivers who can schedule their charging within those conditions may reduce their costs considerably.

However, the cheapest charging rate does not automatically mean the cheapest overall household bill. Before switching, consider the daytime unit rate, standing charge, charging window, equipment requirements and any exit fees.

The right tariff should work for both your car and your home.

Allowing for charging losses

Not every unit of electricity drawn from your home reaches the vehicle’s battery. Some energy is lost during charging.

Our comparison allows for this by assuming 90% charging efficiency. At 3.5 miles per kWh, an EV needs approximately 28.6kWh from its battery to travel 100 miles. Under that charging assumption, it would draw approximately 31.7kWh from the household supply to replace that energy.

Actual charging losses vary with the vehicle, equipment and conditions.

What if you use public charging?

The figures above apply to home charging. Public charging, particularly rapid charging, can cost considerably more and change the comparison.

If you regularly travel beyond your vehicle’s range, or cannot charge at home, calculate your costs using the mix of charging you expect to use.

For example, a driver charging mostly overnight at home will have a different cost profile from someone relying on motorway rapid chargers. Both should assess the vehicle against their own routine.

Looking beyond fuel and electricity

Energy savings can be meaningful, but choosing your next vehicle also involves considering:

• Purchase price or monthly finance payments.
• Insurance, servicing and tyres.
• Vehicle tax and any relevant company-car taxation.
• Home charger installation.
• Range, journey patterns and charging availability.
• Depreciation or the terms of your lease agreement.

Business owners should also consider how charging fits around employees’ working days, particularly where vehicles are taken home or shared between drivers.

*Prices checked 14 October 2026. Fuel figures are UK weekly averages dated 12 October 2026. Electricity rates vary by region, payment method and tariff; Ofgem’s quoted average covers Great Britain, not Northern Ireland. Calculations use UK imperial mpg and unrounded inputs before rounding the results. Energy costs exclude home charger installation and household standing charges. Actual consumption varies with weather, speed, load, driving style and vehicle. This is an energy-cost comparison, not a total cost of ownership assessment.