Public Charging Cost vs Home Charging: Worked Example With Stated Assumptions
The question behind public charging cost vs home charging is really two smaller questions: what does each car use per mile, and what does that energy cost where you buy it. Answer those two and the comparison is arithmetic. This page answers them in order, states the assumptions openly, and then shows the result at several annual mileages so you can see how the answer scales. Where the page leaves something out — purchase price, depreciation, insurance, servicing and tax — it says so by name.
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, 35 US MPG, electricity at 25 cents per kWh and 3.8 miles per kWh — the petrol car costs about $0.11 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. That is the point this page works through for public charging cost vs home charging.
public charging cost vs home charging: Assumptions used on this page
On this page, public charging cost vs home charging is the case in point: 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 | 35 US MPG | Assumption |
| Electricity price | 25 cents per kWh | Example price |
| EV efficiency | 3.8 miles per kWh | Assumption |
| Annual mileage | 15,000 miles | Example |
public charging cost vs home charging: How the EV versus petrol comparison works
On this page, public charging cost vs home charging 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.
public charging cost vs home charging: Worked example: the same distance, two energy bills
Take a driver covering 15,000 miles a year. The petrol car does 35 MPG and petrol costs $3.85 per gallon as an example price, so its cost per mile is $3.85 ÷ 35 = $0.11, and 15,000 miles cost $1,650.00 a year. The EV does 3.8 miles per kWh and electricity costs 25 cents per kWh as an example price, so its cost per mile is $0.25 ÷ 3.8 = $0.07, and 15,000 miles cost $986.84 a year. The difference on fuel and charging alone is $663.16 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.
public charging cost vs home charging: Cost at different annual mileages
The table uses the worked-example assumptions above — petrol at $3.85 per gallon (example), 35 MPG, electricity at 25 cents per kWh (example), 3.8 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. That is the point this page works through for public charging cost vs home charging.
| Annual miles | Petrol cost per year | EV charging cost per year | Difference |
|---|---|---|---|
| 6,000 | $660.00 | $394.74 | $265.26 |
| 8,000 | $880.00 | $526.32 | $353.68 |
| 10,000 | $1,100.00 | $657.89 | $442.11 |
| 12,000 | $1,320.00 | $789.47 | $530.53 |
| 15,000 | $1,650.00 | $986.84 | $663.16 |
| 20,000 | $2,200.00 | $1,315.79 | $884.21 |
Cost per mile and per 100 miles for public charging cost vs home charging
Taking public charging cost vs home charging as the case in point: At the example assumptions, the petrol car costs $0.11 per mile ($11.00 per 100 miles) and the EV costs $0.07 per mile ($6.58 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.
Charging costs: home, public and rapid for public charging cost vs home charging
Charging cost depends on where the electricity comes from, and the spread is wide. Home charging at the example rate of 25 cents per kWh is the cheapest common option; public rapid charging can cost two to three times as much per kWh, and that difference matters more than the car's efficiency. As an example, filling a 82 kWh battery from empty at the home rate used here costs 82 × $0.25 = $20.50; the same charge at double the rate costs $41.00. In practice a battery is rarely charged from empty, and charging losses mean slightly more electricity is drawn from the plug than the battery stores — typically a few percent — so treat the fill-up figure as approximate. Work out your own mix of home and public charging, price each part separately, and only then compare the totals. A driver who charges at home overnight will beat the figures on this page; a driver who relies on rapid chargers may not.
What the comparison leaves out — and why it matters for public charging cost vs home charging
On this page, public charging cost vs home charging is the case in point: 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.
public charging cost vs home charging: Common mistakes
- On this page, public charging cost vs home charging is the case in point: 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.
- On this page, public charging cost vs home charging is the case in point: 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.
- 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. That is the point this page works through for public charging cost vs home charging.
- For public charging cost vs home charging, the point is this: Treating the example prices on this page as current prices is the last mistake. Fuel and electricity prices move constantly, so always substitute the prices you actually pay before trusting any saving.
Related calculations for public charging cost vs home charging
On this page, public charging cost vs home charging is the case in point: 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.
- EV vs Petrol Cost Calculator Australia
- EV vs Petrol Cost Over 10 Years
- Should I Buy an EV or Petrol Car
- EV Maintenance Cost vs Petrol
- Use the calculator
- Browse all ev vs petrol pages
Putting your figure to work for public charging cost vs home charging
On this page, public charging cost vs home charging is the case in point: The method earns its keep when you run it on your own numbers. Measure your real cost per mile for each car — your prices, your efficiency, your charging mix — and you can price a journey before you leave and compare two cars on equal terms instead of brochure claims. Keep a small log of date, miles, energy and price, and look at it monthly: a winter efficiency dip, a change in your charging mix and a slow cost creep all show up fast, and each one is something you can act on.
Frequently asked questions
How sensitive is the saving to the electricity price?
On this page, public charging cost vs home charging is the case in point: Very sensitive. 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.
How many kWh does it take to charge an EV?
Taking public charging cost vs home charging as the case in point: 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.
What affects an EV's miles per kWh?
Taking public charging cost vs home charging as the case in point: Driving speed, temperature, heating and air conditioning, tyre pressures and how much town versus motorway driving you do. Cold weather and high speeds reduce miles per kWh, while gentle town driving usually improves it. Measure yours over several weeks rather than trusting a single trip.
What is excluded from the EV versus petrol comparison?
On this page, public charging cost vs home charging is the case in point: Purchase price, depreciation, insurance, servicing, tyre wear and tax. 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.
Can I use the same method for a diesel car?
On this page, public charging cost vs home charging is 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.