The EV vs Petrol Calculator answers the narrowest and most answerable question in the electric-car debate: for the driving you actually do, what does a year of energy cost in an EV versus a petrol car? Enter annual miles, the EV's consumption, your electricity price, the petrol car's MPG, and the fuel price, and it prices both years side by side.
How It Works
Parameters
| Input | Required | Meaning | |---|---|---| | Miles per year | Yes | Your annual driving | | EV kWh per 100 miles | Yes | The EV's consumption figure | | Electricity price | Yes | Per kWh, your tariff | | Petrol MPG | Yes | US miles per gallon | | Petrol price | Yes | Per gallon |
Worked example
You drive 12,000 miles a year. The EV uses 30 kWh per 100 miles and home electricity costs 576**, about 4.8 cents a mile. The petrol car at 30 MPG burns 400 gallons at 1,400**, about 11.7 cents a mile. The calculator's headline: **0.45 per kWh cost $1,620 a year, more than the petrol car, which is why where you charge matters as much as what you drive.
Finding your honest inputs
The EV consumption figure should come from the car's trip computer over a season, not the brochure: official ratings (around 25 to 30 kWh per 100 miles for efficient models, 35-plus for large SUVs and trucks) flatter winter, motorway, and towing reality by 15 to 30%. Charging losses live in the gap between wall and battery, roughly 10%, so a car reporting 30 kWh per 100 miles from its battery draws about 33 from the wall; entering the wall figure is the honest comparison. Electricity price should be your marginal home tariff, or a usage-weighted blend if you charge away from home. For petrol, use your car's real MPG from fill-ups rather than its window-sticker figure for the same reason: both sides of the comparison deserve the same skepticism.
What this comparison deliberately leaves out
Energy is one line of ownership cost, and not always the largest. Purchase price and depreciation typically dominate a 5-year view (EVs have historically depreciated faster, partly offsetting fuel savings), insurance often runs higher for EVs, maintenance runs lower (no oil, fewer brake jobs thanks to regenerative braking, but tyres wear faster under torque and weight), and home charger installation is a one-off cost of roughly 2,000 that belongs in a first-year comparison. The calculator answers the energy question cleanly rather than smearing assumptions across all of them; for the full picture, add your own depreciation and insurance quotes to the annual saving it reports and judge the total.
Sensitivity: the two prices that decide it
Run the calculator twice more before concluding anything: once with petrol 50 cents higher (a normal year's price movement) and once with your electricity at your tariff's peak rate. The comparison's answer flips for many drivers somewhere inside that box, especially low-mileage ones: at 6,000 miles a year the example's saving halves to about 1,373 and dominates most other line items. High-mileage drivers, home chargers, and cheap overnight tariffs are the EV's best case; low mileage and public-charging dependence are its worst, and the calculator prices your specific corner of that map.
Limitations
The model is US-unit based (miles, US gallons, kWh) and energy-only: it adds no charging-loss factor beyond what your entered consumption includes, models no time-of-use tariff structure, and holds prices constant for the year. Litres and kilometres need converting before entry. It is a scenario comparison, not an ownership-cost guarantee; real prices and real consumption will move around the inputs.
Frequently Asked Questions
Why does home charging change the answer so much?
Because the electricity price input can differ threefold between a home overnight tariff and public rapid charging, and the EV cost is directly proportional to it. The petrol side has no equivalent lever; fuel retail prices vary by cents, not multiples.
Should I include charging losses?
Yes, ideally: use consumption measured at the wall (a smart charger's report) or add about 10% to the car's battery-side figure. The calculator applies exactly the number you enter, so the honesty of the input is the honesty of the result.
Does an EV always win on energy cost?
No. Low annual mileage, expensive public charging, a very efficient petrol car (50 MPG hybrids exist), or cheap fuel can each narrow or reverse the gap. That is precisely why the comparison takes your numbers rather than asserting a universal answer.