Is It Worth Buying an EV Calculator: Formula, Tables and What Is Left Out

If you want a straight answer on is it worth buying an ev calculator, start with the maths, not a headline figure. This page works through the formula step by step, runs a worked example with every assumption stated in full, and gives you tables you can read your own numbers off. Nothing here is presented as a current price or a measured efficiency: every figure is labelled as an assumption or an example, and the method works with whatever numbers you substitute.

The short answer is that the comparison comes down to cost per mile: the petrol car burns US gallons, so its cost per mile is the price per gallon divided by its MPG, while the EV uses kilowatt-hours, so its cost per mile is the electricity price per kWh divided by its miles per kWh. With the example assumptions on this page — petrol at $3.45 per US gallon, 36 US MPG, electricity at 31 cents per kWh and 4.2 miles per kWh — the petrol car costs about $0.10 per mile and the EV about $0.07 per mile. Those are example figures, not prices you should quote, and the rest of this page shows how they were reached and what would change them.

is it worth buying an ev calculator: Assumptions used on this page

For is it worth buying an ev calculator, the point is this: Every figure in the tables below comes from this assumptions table. Each one is an assumption or an example, not a measured fact about any particular car or a current price. Substitute your own numbers and the method still works.

Input Value used Status
Petrol price $3.45 per US gallon Example price
Petrol efficiency 36 US MPG Assumption
Electricity price 31 cents per kWh Example price
EV efficiency 4.2 miles per kWh Assumption
Annual mileage 10,000 miles Example

is it worth buying an ev calculator: How the EV versus petrol comparison works

On this page, is it worth buying an ev calculator is the case in point: Hold the mileage constant and price the energy each car actually uses. For the petrol car, cost per mile equals the price per gallon divided by its MPG. For the EV, cost per mile equals the price per kWh divided by its miles per kWh. Multiply each cost per mile by the annual mileage and you have the annual fuel and charging bill for each car; subtract one from the other and you have the saving, or the extra cost, under those assumptions. The method is deliberately simple, because a simple method with honest inputs beats a complicated model built on guessed ones. The two numbers that matter most are the electricity price and the petrol car's MPG: a driver who charges at home on a cheap overnight rate will see a very different answer from a driver who relies on public rapid chargers, and a thirsty petrol car widens the gap while an efficient one narrows it.

is it worth buying an ev calculator: Worked example: the same distance, two energy bills

Take a driver covering 10,000 miles a year. The petrol car 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, and 10,000 miles cost $958.33 a year. The EV does 4.2 miles per kWh and electricity costs 31 cents per kWh as an example price, so its cost per mile is $0.31 ÷ 4.2 = $0.07, and 10,000 miles cost $738.10 a year. The difference on fuel and charging alone is $220.24 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 for is it worth buying an ev calculator

The table uses the worked-example assumptions above — petrol at $3.45 per gallon (example), 36 MPG, electricity at 31 cents per kWh (example), 4.2 miles per kWh. 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 $442.86 $132.14
8,000 $766.67 $590.48 $176.19
10,000 $958.33 $738.10 $220.24
12,000 $1,150.00 $885.71 $264.29
15,000 $1,437.50 $1,107.14 $330.36
20,000 $1,916.67 $1,476.19 $440.48

is it worth buying an ev calculator: Cost per mile and per 100 miles

At the example assumptions, the petrol car costs $0.10 per mile ($9.58 per 100 miles) and the EV costs $0.07 per mile ($7.38 per 100 miles). Per 100 miles is often the easier figure to compare with a fuel receipt or a charging bill, because both are usually priced in round numbers per hundred miles of driving. If you know your own MPG and your own prices, the same two divisions give your own figures: fuel price per gallon divided by MPG, and electricity price per kWh divided by miles per kWh.

is it worth buying an ev calculator: Break-even: how many miles before the EV pays back the price gap

A break-even figure needs one more assumption: the price difference between the two cars. Suppose, as an example only, the EV costs $12,000.00 more than the comparable petrol car. The fuel and charging saving under this page's assumptions is $0.02 per mile, so the break-even distance is $12,000.00 ÷ $0.02 = 544,865 miles. At 10,000 miles a year that is about 54.5 years of driving. That figure counts fuel and charging only. It excludes insurance, depreciation, servicing differences, tyre wear, tax and any grants or incentives — name them, do not hide them — and each one moves the real break-even point. Depreciation alone can outweigh years of fuel savings, and insurance can differ enough to matter. A break-even number that hides those costs is not a like-for-like comparison, so use this page's figure as a starting point and add the excluded items with stated assumptions before deciding anything.

What the comparison leaves out — and why it matters for is it worth buying an ev calculator

Taking is it worth buying an ev calculator as the case in point: Treat the saving on this page as a fuel-and-charging figure, not a total-cost verdict. It leaves out the price difference between the cars, depreciation, insurance, servicing, tyres and tax, and it assumes one electricity price when real charging is a blend of cheap home charging and expensive public rapid charging. A driver who charges at home will do better than these figures; a driver who lives on rapid chargers may do worse. Add the excluded items with stated assumptions if you want the full comparison.

Common mistakes for is it worth buying an ev calculator

  • For is it worth buying an ev calculator, the point is this: Forgetting charging losses is another: slightly more electricity is drawn from the plug than the battery stores, so dividing the battery size by the miles driven understates the real cost per mile by a few percent.
  • Comparing a laboratory test figure against a real-world figure tells you nothing about the car and everything about the methods. Keep the method constant — real-world against real-world — and the comparisons become meaningful. That is the point this page works through for is it worth buying an ev calculator.
  • On this page, is it worth buying an ev calculator is the case in point: Forgetting that winter changes EV efficiency is easy to miss. Cold weather reduces an EV's miles per kWh noticeably, so a saving calculated on summer figures will overstate the winter result.
  • For is it worth buying an ev calculator, the point is this: Using the same electricity price for every charge hides the real cost. A driver who mixes home and public charging has two different prices, and averaging them into one number without weighting by how much energy comes from each is a common error.

Related calculations for is it worth buying an ev calculator

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 this page works through for is it worth buying an ev calculator.

is it worth buying an ev calculator: Putting your figure to work

For is it worth buying an ev calculator, the point is this: Use the result as a tool, not a verdict. Re-run the two divisions with your own prices and efficiencies whenever they change, and the comparison stays honest. A monthly log — miles, energy used, price paid — is enough to spot the patterns that matter: colder months cost more per mile for an EV, a new charging habit shifts the average, and a petrol car driven more in town drifts the other way. Measured figures beat remembered ones, and the method on this page is built for measured figures.

Frequently asked questions

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

Use the same mileage for both cars. 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. That is the point this page works through for is it worth buying an ev calculator.

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

For is it worth buying an ev calculator, the point is this: Not always. 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.

Can I use the same method for a diesel car?

Taking is it worth buying an ev calculator as the case in point: Yes. A diesel car uses the same petrol-side formula — fuel price per gallon divided by MPG — with diesel prices and diesel MPG. The EV side is unchanged. Compare the two cost-per-mile figures the same way, and remember the same exclusions apply.

Why do EV running-cost figures disagree so much?

On this page, is it worth buying an ev calculator is the case in point: Because the inputs differ. Two honest calculations can give very different answers if one assumes cheap home charging and the other assumes public rapid charging, or if one uses a high-mileage year and the other a low one. Always ask what electricity price, what MPG and what mileage a figure was calculated with before comparing it with another.

What does miles per kWh mean?

Taking is it worth buying an ev calculator as the case in point: It is the EV equivalent of MPG: how many miles the car travels on one kilowatt-hour of electricity. Higher is more efficient. Divide the electricity price per kWh by miles per kWh to get the EV's cost per mile, in the same way you divide the fuel price per gallon by MPG for a petrol car.