What this calculator does
The running cost argument for an electric car is usually made with a single number that hides every assumption behind it. The honest comparison needs four: how much energy each car uses per hundred kilometres, and what each form of energy costs you.
Put those in and the gap is usually large. At 16 kWh per 100 km and 30 cents a kilowatt hour the electric car costs $4.80 per hundred kilometres. A petrol car at 8 litres and $1.90 costs $15.20. Over 15,000 km a year that is a difference of $1,560.
The formula
Both sides are the same calculation in different units: consumption per 100 km multiplied by the price of the energy. The useful extra step is inverting it. Setting the two costs equal and solving for the fuel price gives petrol price = EV cost per 100 km ÷ litres per 100 km, which is the pump price at which petrol would become the cheaper option. Doing the same for electricity gives the tariff at which the advantage disappears.
| Term | Meaning |
|---|---|
| kWh/100 km | Energy drawn from the wall per hundred kilometres. Use the figure from the car rather than the brochure, since charging losses count. |
| L/100 km | The petrol car's real consumption, which is usually worse than its rated figure. |
| Break-even price | The price at which the two cost the same. Everything below it favours one car and everything above favours the other. |
The inputs explained
| Field | What to enter |
|---|---|
| Distance driven per year (km) | Kilometres driven in a year. The saving scales directly with this, so a low-mileage driver sees much less of it. |
| EV consumption (kWh/100km) | Energy from the wall per 100 km, not energy into the battery. The difference is the charging loss, usually around 10 per cent. |
| Electricity price ($/kWh) | What you actually pay per kilowatt hour. Overnight or controlled-load tariffs can be a third of the peak rate, and solar can be lower again. |
| Petrol consumption (L/100km) | Real-world litres per 100 km for the petrol car, measured over a few tanks rather than taken from the specification. |
| Petrol price ($/L) | Pump price per litre. |
When to use it
Checking whether the saving survives a tariff rise
Raise the electricity price until the yearly saving reaches zero. On the default figures that happens at 95 cents a kilowatt hour, which is a long way above most retail tariffs, so the comparison is not fragile.
Charging at a public fast charger
Public charging is often two to three times the home rate. Entering it shows how much of the advantage is really an advantage of charging at home rather than of the car itself.
Comparing against a more efficient petrol car
A hybrid at 4.5 L/100 km costs $8.55 per hundred kilometres, which cuts the yearly saving from $1,560 to $563, barely a third of what it was. The comparison is against a specific car, not against petrol in general.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does the petrol price change the saving?
Only the pump price changes.
| Petrol price | Yearly saving by driving electric | Petrol cost per 100 km | Petrol price that would match the EV |
|---|---|---|---|
| $0.60 | $0.00 | $4.80 | $0.60 per litre |
| $1.20 | $720.00 | $9.60 | $0.60 per litre |
| $1.50 | $1,080.00 | $12.00 | $0.60 per litre |
| $1.90 | $1,560.00 | $15.20 | $0.60 per litre |
| $2.20 | $1,920.00 | $17.60 | $0.60 per litre |
| $2.50 | $2,280.00 | $20.00 | $0.60 per litre |
At what electricity price does the advantage disappear?
Only the electricity tariff changes.
| Electricity price | Yearly saving by driving electric | Electric cost per 100 km | Electricity price that would match petrol |
|---|---|---|---|
| $0.08/kWh | $2,088.00 | $1.28 | $0.95 per kWh |
| $0.15/kWh | $1,920.00 | $2.40 | $0.95 per kWh |
| $0.30/kWh | $1,560.00 | $4.80 | $0.95 per kWh |
| $0.45/kWh | $1,200.00 | $7.20 | $0.95 per kWh |
| $0.60/kWh | $840.00 | $9.60 | $0.95 per kWh |
| $0.95/kWh | $0.00 | $15.20 | $0.95 per kWh |
Questions
Does this include servicing, depreciation or the purchase price?
No. It is the energy comparison only. For the full picture the true cost per mile page takes fuel, maintenance, insurance and depreciation together.
Should I use the energy into the battery or from the wall?
From the wall, because that is what the meter charges you for. Charging loses roughly 10 per cent, so a car that puts 14.5 kWh into the battery draws about 16 from the wall.
What if I charge mostly on solar?
Enter the value of that solar, which is the feed-in tariff you gave up rather than zero. Using surplus solar you would otherwise export at 5 to 8 cents is genuinely close to free motoring.
Why is the break-even petrol price so low?
Because electricity delivers far more motion per dollar. Petrol would have to fall to around 60 cents a litre, on these figures, before it matched. That has not happened in most markets for decades.
Does cold weather change this?
Yes. Winter consumption can be 20 to 30 per cent higher for an electric car because cabin heating comes from the battery. Run the calculation again with a winter consumption figure to see the worst case.
For one charging session rather than a year, see EV home charging cost and time. For the whole cost of running a car there is true cost per mile, and for a single journey trip fuel cost.