Electric vs Petrol Car Cost: When the Maths Flips

An electric car typically costs about 62% less to run per kilometre than a comparable petrol model — yet it can still sit thousands behind on total cost for the first six or seven years of ownership. That tension between cheaper running and a dearer purchase price is what the electric vs petrol car cost comparison really turns on, and it is exactly where most quick comparisons trip up.

This guide takes the comparison apart: how it is built, a full worked example using country-neutral numbers, and the break even point where the maths tips in the electric car's favour. The same logic sits behind the electric car vs petrol calculator, which estimates running costs and the distance at which an electric car becomes the cheaper option.

What the electric vs petrol car cost comparison actually measures

At its core, the comparison weighs the full cost of running each car over the same distance and time — not just the price on the windscreen. It folds in the purchase price, energy used per kilometre, servicing, and any taxes or incentives that apply where you live. The output is usually one of two things: a total cost of ownership over a set period, or a break even distance where the two cars have cost you the same amount.

The catch is that the two cars almost never win on the same measure. The petrol car tends to win on day one, because it is cheaper to buy. The electric car tends to win on every kilometre after that, because electricity per kilometre is usually far cheaper than fuel. So the comparison is really about working out when the second advantage overtakes the first.

Why the comparison is worth running yourself

Energy prices, vehicle prices, and how far people drive vary enormously between countries and shift over time. A comparison that fits one driver perfectly can mislead another completely. Someone covering long distances reaches the break even point years sooner than someone who barely leaves their town.

Global energy and transport bodies have tracked a long, steady fall in the cost of electric drivetrains and batteries, while fuel prices stay at the mercy of market swings. Because the inputs keep moving, the numbers hold up best when they are run for a specific driver rather than lifted from a headline.

How the comparison is calculated

There are two layers to it. First, the running cost per unit of distance for each car. Second, the break even point, where the running saving has finally clawed back the extra paid upfront for the electric car.

Running cost per 100 kilometres is simply energy used multiplied by energy price. For petrol, that is litres per 100 km times the price per litre. For electric, it is kilowatt hours per 100 km times the price per kilowatt hour. The gap between the two is the saving for every 100 km driven.

Saving per 100 km = (petrol litres/100km × fuel price)
                    − (EV kWh/100km × electricity price)

Break even distance = price premium ÷ (saving per 100 km ÷ 100)
Break even years    = price premium ÷ annual running saving

Where:

• Price premium — how much more the electric car costs to buy than a comparable petrol model
• Saving per 100 km — petrol energy cost minus electric energy cost over the same distance
• Annual running saving — saving per 100 km times yearly distance, plus any difference in servicing
• Break even point — the distance or time at which the two cars have cost the same

A worked example with real numbers

Maya is weighing up an electric car against a comparable petrol model. To keep the example readable anywhere, the figures use generic currency units and metric distance — swap in your own currency and the method still holds.

Here is what she is working with:

• Annual distance: 15,000 km
• Petrol car: 7.0 litres per 100 km, fuel at 1.60 per litre
• Electric car: 17 kWh per 100 km, electricity at 0.25 per kWh
• Electric car purchase premium: 7,000 over the petrol model

Start with energy per 100 km. Petrol comes to 7.0 × 1.60 = 11.20; electric to 17 × 0.25 = 4.25. The electric figure is roughly 38% of the petrol one — a saving of about 62% on energy. In cash terms, Maya keeps 11.20 − 4.25 = 6.95 for every 100 km.

Across 15,000 km — 150 lots of 100 km — petrol fuel costs 150 × 11.20 = 1,680 a year, while electricity costs 150 × 4.25 = 637.50. That leaves an annual running saving of 1,042.50.

Now the premium. Recovering 7,000 at 1,042.50 a year takes 7,000 ÷ 1,042.50 ≈ 6.7 years, or roughly 100,700 km. Before that crossover the petrol car has cost less overall; after it, every kilometre tips further toward the electric car. Feed the same inputs into the electric car vs petrol calculator and it returns the same break even distance and year.

How to use the electric car vs petrol calculator

The electric car vs petrol calculator takes the same inputs used above and hands back the running cost of each car, the annual saving, and the break even distance and year. Your own numbers matter far more than any default here, because the result swings hard on distance and local energy prices.

The inputs cover yearly distance, fuel economy and price for the petrol car, energy use and electricity price for the electric one, and the purchase premium. The outputs show cost per 100 km for each car, the annual and lifetime saving, and the exact point where the two total costs cross.

Common scenarios

High annual distance

A driver covering 30,000 km a year doubles the annual saving to about 2,085 and cuts break even to roughly 3.4 years. The more kilometres, the bigger the gain.

Low annual distance

At 6,000 km a year the saving drops to about 417, which pushes break even past 16 years. At very low mileage the premium may never be repaid inside a normal ownership window, so the petrol car can stay cheaper for good.

A smaller purchase premium

If incentives or a tighter price gap trim the premium to 3,500, break even at 15,000 km a year falls to about 3.4 years.

Servicing differences

Electric cars often have fewer moving parts, so servicing can cost less. Add a 300 yearly servicing saving and the annual saving climbs to 1,342.50, bringing break even forward to about 5.2 years.

Where the comparison trips people up

1. Comparing sticker prices only. The purchase price is one input, not the verdict. A cheaper-looking petrol car can cost more across the whole ownership period once fuel is added up.
2. Ignoring your real distance. Break even leans heavily on yearly kilometres, so using an average instead of your own figure can move the answer by years.
3. Assuming today's prices hold. Fuel and electricity both move. Running a higher and a lower price gives a range rather than one brittle number.
4. Forgetting the ownership window. A break even of eight years means little if the car gets sold after three.
5. Treating incentives as permanent. Incentives and tax treatment change over time and differ by region, so a comparison built on them can date fast.

Related calculations and tools

Comparing two cars naturally spills into other running-cost questions. These tools pick up where this one leaves off:

• Car Running Cost Calculator — What your car really costs each year.
• Car Running Cost Calculator — What your car really costs each year.
• Car Depreciation Calculator — See how much your car actually loses.

Frequently asked questions

Is an electric car cheaper than a petrol car overall?

It depends on three things: distance, energy prices, and how long the car is kept. An electric car is usually cheaper to run per kilometre — often by around 60% on energy alone — but it costs more to buy. The total only tips in its favour once that running saving has repaid the higher purchase price, which is the break even point. For an average distance, that point often lands within five to seven years. Drive very little and it can fall outside a normal ownership window, leaving the petrol car cheaper overall.

How many kilometres until an electric car pays off?

Take the purchase premium and divide it by the saving per kilometre. In the worked example, a 7,000 premium and a 6.95 saving per 100 km put break even near 100,700 km — about 6.7 years at 15,000 km a year. A smaller premium, cheaper electricity, dearer fuel, or more distance all pull that number down. Because it swings so widely, a figure drawn from your own driving beats any general average, and a calculator pinpoints the exact crossover.

What makes an electric car cheaper to run than petrol?

Mostly energy cost per kilometre. Electricity priced per kilowatt hour usually moves a car a given distance for less than fuel priced per litre, partly because electric motors turn more of their energy into motion. In the worked example, the electric car's energy cost is about 38% of the petrol figure. Servicing can stretch the gap further, since electric cars tend to have fewer moving parts. These savings stack up with every kilometre, so high-mileage drivers feel the biggest yearly difference and hit break even soonest.

How does annual mileage change the electric vs petrol car cost?

Mileage is one of the strongest levers in the whole comparison. The saving is earned per kilometre, so the more driven each year, the faster the premium gets repaid. Double the distance from 15,000 to 30,000 km a year and break even roughly halves, from about 6.7 years to 3.4. Cut it to 6,000 km a year and it stretches past 16. That is why the same two cars can hand two drivers opposite answers — and why a real distance matters more than any average.

Sources and methodology

These figures come from a transparent method rather than a single dataset. Running cost per 100 km is energy used times energy price for each car, and break even is the purchase premium divided by the annual running saving. Every number in the worked example was checked to compute correctly before publication.

For the wider context on energy and vehicle cost trends, the comparison leans on global bodies rather than any one country's tax authority:

• OECD — research on transport, energy, and environmental economics
• Peer-reviewed total cost of ownership studies on electric and combustion vehicles, available through academic databases such as SSRN

The bottom line

The electric vs petrol car cost question rarely has a single answer, because it hinges on distance, energy prices, the purchase premium, and how long the car stays on the drive. The petrol car usually leads at purchase; the electric car leads on every kilometre after. Where those two lines cross is the break even point — around 6.7 years or 100,700 km in the example above. Running your own figures turns a vague debate into one specific number to decide on.