Guide
What it really costs to drive 100 miles
The honest fuel and charging maths for petrol, diesel and electric in 2026, including the catch that decides whether an electric car is cheap to run or dearer than petrol.
The cost of covering 100 miles is one of the few numbers that lets you compare petrol, diesel and electric on level ground. It cuts through headline pump prices and confusing tariffs. The answer, as of September 2026, is clear on one point and slippery on another, and the slippery part is where most of the money hides.
The numbers, up front
Using typical figures for each type of car and prices as they stand in September 2026, here is roughly what 100 miles costs in fuel or electricity alone.
Cost to drive 100 miles, September 2026
- Petrol car, about 45 miles per gallon at 162p a litre: around £16
- Diesel car, about 55 miles per gallon at 184p a litre: around £15
- Electric car charged at home on an off peak tariff, about 3.5 miles per kWh at 7p a unit: around £2
- Electric car charged at home on a standard rate, at about 25p a unit: around £7
- Electric car charged on a public rapid charger, at about 80p a unit: around £23
Assumes 45 mpg petrol, 55 mpg diesel and 3.5 miles per kWh for the electric car. Your own figures will vary with the car, the driving and the day. See the assumptions below.
What the comparison is really telling you
Look at the spread. An electric car can cost a pound or two for 100 miles or well over twenty pounds for the very same journey, depending only on where it charges. That single fact matters more than the choice of car. Petrol and diesel, by contrast, land close together and stay there, because there is nowhere cheap or expensive to fill up in the way there is to charge.
Electric is cheapest by a mile, but only at home overnight. A dedicated overnight electricity tariff for electric cars is what produces those headline savings. Charge on it and nothing on four wheels comes close. Without a driveway and a home charger, you lose access to the cheap rate, and the sums change completely.
Public rapid charging can cost more than petrol. This is the catch the adverts skip. Pay as you go rapid charging on the motorway network runs to around 80p a unit, and at that rate a 100 mile top up can cost more than the same distance in a petrol car. An electric car is not automatically cheap to run. It is cheap to run at home and potentially expensive away from it.
Diesel still earns its keep on high mileage. Diesel costs more per litre than petrol, yet a diesel engine squeezes more miles from each one, so for the big annual mileages the cost per 100 miles edges below petrol. For low mileage town driving the pump premium wins and petrol is the cheaper pick.
The assumptions, in plain sight
None of these numbers is a law of nature, so here is exactly what sits behind them. Petrol at 45 miles per gallon and diesel at 55 are reasonable real world figures for a typical family car, not the optimistic official ones. Fuel at 162p and 184p a litre reflects the UK average in September 2026, and you can beat both by choosing a cheap forecourt. The electric car is assumed to manage 3.5 miles from each kWh, which suits a mainstream model in mixed driving. Charging costs of 7p, 25p and 80p a unit stand in for a good overnight tariff, a standard home rate and public rapid charging respectively. Change any of these and the answer moves, which is precisely the point.
How to work out your own number
For a petrol or diesel car, check the real price near you rather than the national average, because a few pence a litre adds up over a year. The price finder ranks every forecourt within five miles of your postcode. For an electric car, the figure that decides everything is what you pay per unit, so it is worth knowing the going rate on the networks near you before you rely on public charging. Our EV charging costs page shows chargers around you with an indication of what each network charges, so the twenty pound surprise never happens on the forecourt.
Common questions
How much does it cost to drive 100 miles in 2026?
As of September 2026, roughly 16 pounds in a typical petrol car and 15 pounds in a diesel. An electric car ranges from about 2 pounds charged at home on an off peak tariff to around 23 pounds on a public rapid charger, so where an electric car charges matters more than the choice of car.
Is an electric car always cheaper to run than petrol?
No. Charged at home on an overnight tariff an electric car is far cheaper, at around 2 pounds for 100 miles. But public rapid charging can cost around 80p a unit, which works out to more than driving the same distance in a petrol car. Electric is cheap at home and potentially dear away from it.
Is diesel or petrol cheaper to run?
Diesel costs more per litre but returns more miles per gallon, so for high annual mileage it works out slightly cheaper per 100 miles. For low mileage town driving the higher diesel pump price wins and petrol is cheaper. The gap is small either way.
How can I lower my running costs?
For petrol or diesel, buy at a competitive forecourt rather than the national average, which the Petrol Tracker price finder helps you do. For electric, charge at home on an off peak tariff wherever possible and check public charging rates before you rely on them.