EV Payback Calculator: What the Maths Says With Real Assumptions

If you want a straight answer on ev payback 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 $3.85 per US gallon, 32 US MPG, electricity at 28 cents per kWh and 4.0 miles per kWh — the petrol car costs about $0.12 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.

ev payback calculator: Assumptions used on this page

For ev payback 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 $3.85 per US gallon Example price
Petrol efficiency 32 US MPG Assumption
Electricity price 28 cents per kWh Example price
EV efficiency 4.0 miles per kWh Assumption
Annual mileage 10,000 miles Example

How the EV versus petrol comparison works for ev payback calculator

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. That is the point this page works through for ev payback calculator.

Worked example: the same distance, two energy bills for ev payback calculator

Take a driver covering 10,000 miles a year. The petrol car does 32 MPG and petrol costs $3.85 per gallon as an example price, so its cost per mile is $3.85 ÷ 32 = $0.12, and 10,000 miles cost $1,203.12 a year. The EV does 4.0 miles per kWh and electricity costs 28 cents per kWh as an example price, so its cost per mile is $0.28 ÷ 4.0 = $0.07, and 10,000 miles cost $700.00 a year. The difference on fuel and charging alone is $503.12 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 ev payback calculator

The table uses the worked-example assumptions above — petrol at $3.85 per gallon (example), 32 MPG, electricity at 28 cents per kWh (example), 4.0 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 $721.88 $420.00 $301.88
8,000 $962.50 $560.00 $402.50
10,000 $1,203.12 $700.00 $503.12
12,000 $1,443.75 $840.00 $603.75
15,000 $1,804.69 $1,050.00 $754.69
20,000 $2,406.25 $1,400.00 $1,006.25

Cost per mile and per 100 miles for ev payback calculator

At the example assumptions, the petrol car costs $0.12 per mile ($12.03 per 100 miles) and the EV costs $0.07 per mile ($7.00 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.

ev payback 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 $6,000.00 more than the comparable petrol car. The fuel and charging saving under this page's assumptions is $0.05 per mile, so the break-even distance is $6,000.00 ÷ $0.05 = 119,255 miles. At 10,000 miles a year that is about 11.9 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.

ev payback calculator: What the comparison leaves out — and why it matters

For ev payback calculator, the point is this: Before treating any EV saving as a promise, check what was excluded. 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 for ev payback calculator

  • For ev payback calculator, the point is this: Comparing a car's best-case efficiency with another's everyday figure is another trap. Brochure efficiency is measured in controlled conditions; your real miles per kWh or MPG will be lower, and the comparison only works when both cars are measured the same way.
  • Taking ev payback calculator as the case in point: 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.
  • On this page, ev payback calculator is the case in point: Mixing US and imperial gallons is the biggest, because it shifts the answer by about 20 percent with no warning. A UK imperial gallon is about 4.55 litres; a US gallon is about 3.79 litres, so the same car has a higher MPG figure in imperial gallons than in US gallons.
  • 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. That is the point this page works through for ev payback calculator.

ev payback calculator: Related calculations

Taking ev payback calculator as the case in point: These pages continue from here: the same method on a neighbouring question, or the calculator that runs the arithmetic for you.

ev payback calculator: Putting your figure to work

Taking ev payback calculator as the case in point: Putting the figure to work is where the method pays off. Once you know your own cost per mile for each car, measured with your own prices and efficiencies, you can price any journey before you set off and compare cars honestly, because you are comparing measured figures rather than brochure claims. Keep a simple log — date, miles, energy used, price paid — and review it monthly. Patterns show up quickly: a winter dip in EV efficiency, a motorway improvement, a slow rise in your charging cost that points to more public charging than you planned. 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

How many kWh does it take to charge an EV?

It depends on the battery size and how empty it is. A charge from near-empty to full takes roughly the battery's capacity in kWh, plus a few percent for charging losses. Divide the kWh drawn by the miles driven afterwards and you have the car's real miles per kWh for that period. That is the point this page works through for ev payback calculator.

Can I use the same method for a diesel car?

Taking ev payback 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.

What does miles per kWh mean?

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. That is the point this page works through for ev payback calculator.

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

On this page, ev payback calculator is the case in point: 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.

Does an EV cost more to insure?

Taking ev payback calculator as the case in point: Insurance is not part of the fuel-and-charging maths on this page, and it can differ between an EV and a petrol car for reasons that have nothing to do with energy: repair costs, parts availability and the car's value all play a part. Get a quote for both cars before comparing total costs.