Petrol, diesel or electric: what is actually cheaper to run?

Most comparisons pick one petrol price and one electricity price and call it a day. That misses the point entirely: fuel barely varies by where you buy it, while electricity swings enormously between charging at home overnight and paying for a motorway rapid charger. Comparing a car's worst charging habit to its best fuel habit, or the reverse, produces whatever answer the person writing it wanted.

Convert everything to cost per 100 km. For a combustion car, that is the fuel price times how many litres it burns over 100 km. For an EV, it is the price per kWh times how many kWh it uses over 100 km. Once both sides speak the same unit, the comparison stops being about the label on the car and starts being about the number.

Two honest caveats. This uses public charging, which is the dearest way to charge: at home overnight the electric figure typically falls by more than half. And the consumption figures are averages, not your car. Put your own numbers in and the ranking can shift.

A combustion car burning around 6 litres per 100 km at a mid-range fuel price lands in a fairly narrow band, because fuel prices themselves do not vary that wildly. An EV using around 15 to 20 kWh per 100 km can cost a fraction of that charged mostly at home, roughly the same as fuel on public AC, or noticeably more than fuel if it lives exclusively on the most expensive rapid chargers.

In other words, an EV can be the cheapest option on the road or one of the priciest, and the difference is not the car, it is where you plug it in. Fuel does not have that swing: the worst petrol station and the best one are close together compared with the worst and best charging option.

Purchase price and depreciation still separate combustion and electric far more than running cost does, and vary by market and model, so they belong in the decision, just not in this comparison.

Servicing tends to run cheaper for EVs, fewer moving parts, no oil changes, though tyres and, eventually, the battery are real costs of their own.

Your actual routine matters more than any average. A driver who can charge at home every night lives in a different cost world to one who relies entirely on public rapid charging, even in an identical car.

Is an EV always cheaper to run than petrol?

Not always. Charged mostly at home, usually yes and by a wide margin. Relying only on the most expensive public rapid chargers can erase that advantage or reverse it.

Is diesel cheaper to run than petrol?

Often close per 100 km once you account for diesel's better fuel economy, though the exact answer depends on local prices and how you drive. Comparing the real numbers beats assuming.

Does this comparison include the cost of the car itself?

No, deliberately. Purchase price and depreciation are real and belong in a buying decision, but mixing them into running cost hides which number is actually driving the answer.