Electric Car Running Costs vs Petrol: What the Maths Really Says

If you want a straight answer on electric car running costs vs petrol, start with the maths, not a guess. This page works through the formula step by step, runs a worked example with the assumptions stated in full, and gives you a table you can read your own numbers off. Everything here uses the same definitions throughout, so the figures in the table match the figures in the example.

The short version is that electric car running costs vs petrol comes down to two measurements you can take yourself: how far you drove, and how much fuel you used. Get those two right and the rest is arithmetic. Get either one wrong — a half-full tank, a trip meter that was never reset, a gallon confused with a litre — and the answer is meaningless, however carefully you divide.

How the EV versus petrol cost comparison works — electric car running costs vs petrol

To compare an EV with a petrol car fairly, hold the mileage constant and price the energy each one actually uses. That is the point to carry into electric car running costs vs petrol: the answer follows from the assumptions, so write yours down before you trust the result. A petrol car burns gallons, so its cost per mile is the price per gallon divided by its MPG. An EV uses kilowatt-hours, so its cost per mile is the price per kWh divided by its miles per kWh. This page works the example with stated assumptions: petrol at $3.45 per gallon (example price), 36 MPG for the petrol car, electricity at $0.25 per kWh (example price), and 4.0 miles per kWh for the EV. Change any one of those and the answer moves — cheap home charging helps the EV, expensive public rapid charging hurts it, and a very efficient petrol car narrows the gap. The sections below show the result at several mileages so you can see how the saving scales, and they name what is excluded: purchase price, depreciation, insurance, servicing and tax are not in this fuel-cost maths.

Worked example: the same miles, two fuel bills — electric car running costs vs petrol

Take a driver covering 12,000 miles a year. For electric car running costs vs petrol, the same reasoning applies — substitute your own prices and efficiencies and the steps on this page still hold. The petrol car in this example does 36 MPG and petrol costs $3.45 per gallon as an example price, so its cost per mile is $3.45 ÷ 36 = $0.10 per mile, and 12,000 miles cost 12,000 × $0.10 = $1,150.00 a year. The EV does 4.0 miles per kWh and electricity costs $0.25 per kWh as an example price, so its cost per mile is $0.25 ÷ 4.0 = $0.06 per mile, and 12,000 miles cost $750.00 a year. The difference on fuel and charging alone is $400.00 a year in the EV's favour under these assumptions. Now change one input and watch the answer move: if the EV is charged mostly at a public rapid charger at, say, double the home electricity price used here, its annual charging cost doubles and most of the saving disappears. If the petrol car is driven mainly in town at lower MPG, the petrol bill rises and the saving grows. That sensitivity is the real lesson — the answer is only as solid as the assumptions, so write yours down before you believe the result.

Cost at different annual mileages — electric car running costs vs petrol

The table uses the worked-example assumptions above — petrol at $3.45 per gallon (example), 36 MPG, electricity at $0.25 per kWh (example), 4.0 miles per kWh. That is the point to carry into electric car running costs vs petrol: the answer follows from the assumptions, so write yours down before you trust the result. The gap grows with mileage, which is why high-mileage drivers see the biggest fuel-cost difference and low-mileage drivers see the smallest.

Annual miles Petrol cost per year EV charging cost per year Difference
6,000 $575.00 $375.00 $200.00
10,000 $958.33 $625.00 $333.33
12,000 $1,150.00 $750.00 $400.00
15,000 $1,437.50 $937.50 $500.00
20,000 $1,916.67 $1,250.00 $666.67

What the comparison leaves out — and why it matters — electric car running costs vs petrol

Before treating any EV saving as a promise, check what was excluded. Read the figures on this page about electric car running costs vs petrol as a worked illustration, not as prices or efficiencies you should quote elsewhere. This page's maths covers fuel and charging only. It does not include the price difference between the cars, depreciation, insurance, servicing, tyres, or tax — all of which differ between an EV and a petrol car and all of which change the real answer. It also assumes a single electricity price, while real charging mixes cheap home charging with expensive public rapid charging, and the mix matters more than the headline rate. A driver who charges at home overnight will beat the figures here; a driver who relies on rapid chargers may not. Work out your own mix, price it honestly, and only then compare the totals.

Common mistakes — electric car running costs vs petrol

Five mistakes cover most wrong MPG figures. For electric car running costs vs petrol, the same reasoning applies — substitute your own prices and efficiencies and the steps on this page still hold. Mixing US and imperial gallons is the biggest, because it shifts the answer by about 20 percent with no warning. Using one tank instead of an average is next — a single fill is noisy, and a pump that clicks off early can add a phantom gallon. Forgetting to reset the trip meter at the fill is another, because it silently adds miles from the previous tank. Using the fuel light or the gauge instead of the pump reading is worse still, since gauges are approximate by design. Finally, comparing figures measured different ways — a laboratory test figure against a real-world figure, or a dashboard estimate against a brim-to-brim measurement — tells you nothing about the car and everything about the methods. Keep the method constant and the comparisons become meaningful.

Related calculations — electric car running costs vs petrol

If this page answered your question, these pages take the next step — the same method applied to a closely related question, or the calculator that does the arithmetic for you. That is the point to carry into electric car running costs vs petrol: the answer follows from the assumptions, so write yours down before you trust the result.

Putting your electric car running costs vs petrol figure to work

Putting the figure to work is where the method pays off. Read the figures on this page about electric car running costs vs petrol as a worked illustration, not as prices or efficiencies you should quote elsewhere. Once you know your own MPG, measured brim-to-brim over several tanks, you can price any journey before you set off: multiply the miles by the fuel price divided by your MPG, and the answer is the fuel cost of that trip at that example price. You can also compare cars honestly, because you are comparing measured figures rather than brochure claims. Keep a simple log — date, miles, gallons, price — and review it monthly. Patterns show up quickly: a winter dip, a motorway improvement, a slow decline that points to tyre pressures or a change in routes. The log turns a vague feeling about fuel use into a number you can act on, and that is the whole point of measuring in the first place.

Frequently asked questions

Is an EV always cheaper to run than a petrol car?

Not always. Read the figures on this page about electric car running costs vs petrol as a worked illustration, not as prices or efficiencies you should quote elsewhere. On fuel and charging alone, an EV is usually cheaper per mile when it charges mostly at home at an example electricity price, but the answer flips if it relies on expensive public rapid charging or if the petrol car is very efficient. Purchase price, depreciation, insurance and servicing are not in the fuel-cost maths, so a full comparison has to include them before calling either car cheaper overall.

How do I work out my own EV versus petrol saving?

Use the same mileage for both cars. Read the figures on this page about electric car running costs vs petrol as a worked illustration, not as prices or efficiencies you should quote elsewhere. For the petrol car, divide the fuel price per gallon by its MPG to get cost per mile. For the EV, divide the electricity price per kWh by its miles per kWh. Multiply each by your annual miles and subtract. Use your own prices — especially your real charging mix of home and public charging — rather than the example prices on this page.

What is excluded from the EV versus petrol comparison?

Purchase price, depreciation, insurance, servicing, tyre wear and tax. Read the figures on this page about electric car running costs vs petrol as a worked illustration, not as prices or efficiencies you should quote elsewhere. This page compares fuel and charging costs only, and says so, because a break-even figure that hides those costs is not a like-for-like comparison. Add them with stated assumptions if you want a total-cost answer.

Does charging at home really make that much difference?

Yes, usually more than any other single factor. For electric car running costs vs petrol, the same reasoning applies — substitute your own prices and efficiencies and the steps on this page still hold. Home charging is typically far cheaper per kWh than public rapid charging, so a driver who charges at home overnight will see a much bigger saving than one who relies on rapid chargers. Work out your own mix of home and public charging and price each part separately for an honest figure.

How sensitive is the saving to the electricity price?

Very sensitive. That is the point to carry into electric car running costs vs petrol: the answer follows from the assumptions, so write yours down before you trust the result. Doubling the electricity price doubles the EV's charging cost per mile, while the petrol side is unchanged. That is why this page states its example prices openly: change the electricity price to the one you actually pay and the saving changes with it, sometimes by enough to change the conclusion.