EV vs Petrol Cost Calculator
Compare running costs, 5-year total cost of ownership, and CO² savings between an EV and a petrol car.
How this is calculated
Petrol cost converts your annual mileage and mpg into litres burned (via an imperial gallon) and multiplies by fuel price. EV cost converts the same mileage into kWh via your EV's efficiency and multiplies by electricity price. The break-even year divides your EV's purchase premium by the annual saving, and CO² saved compares petrol's fixed emission factor (2.31kg per litre) against your grid's carbon intensity.
Fuel is only part of the total cost of ownership gap between EVs and petrol cars. EVs typically have meaningfully lower servicing costs — no oil changes, far fewer moving parts in the drivetrain, and regenerative braking that significantly reduces brake pad and rotor wear compared to a purely friction-braked petrol car. These maintenance savings aren't included in this calculator's break-even figure, so the real-world payback period for many EV owners is often somewhat shorter than the fuel-only estimate here suggests. For your electricity cost and grid carbon intensity inputs, see the Home Electricity Cost by Country calculator and the Electricity Carbon Intensity calculator. If you're financing rather than buying outright, see the Car Buy vs Lease calculator.
Frequently asked questions
- Why does mpg use an imperial gallon?
- To match the price-per-litre and pence-per-kWh convention used throughout this calculator — an imperial gallon is 4.54609 litres. If your mpg figure is in US gallons, convert it first (multiply by roughly 0.833).
- What does break-even year mean?
- How many years of annual fuel savings it takes to recover the extra amount you paid for the EV upfront. If the EV doesn't save money annually (e.g. very low mileage or a very efficient petrol car), break-even is never reached.
- What is grid intensity and why does it matter for CO2?
- The amount of CO2 emitted per kWh of electricity generated, which varies hugely by country depending on the generation mix (heavy coal use vs. nuclear/renewables). A cleaner grid means charging an EV saves more CO2 compared to burning petrol directly.
- Can I use this in my own app?
- Yes — every calculator on Stupidly Clever has a matching REST API and MCP tool that runs the same underlying logic.
- How is the cost comparison calculated?
- Annual petrol cost comes from your mileage divided by mpg (converted to litres via an imperial gallon) times fuel price. Annual EV cost comes from the same mileage divided by your EV's efficiency (miles/kWh) times electricity price. The difference between the two, compared against the EV's purchase premium, gives the break-even year.
- How does electricity tariff affect EV running cost?
- EV running cost scales directly with your electricity price per kWh — a higher tariff narrows (or can eliminate) the cost advantage over petrol, while a lower tariff (e.g. off-peak home charging rates) widens it. Where and when you charge can meaningfully change the economics.
- What is a typical EV efficiency in kWh/100km?
- Most modern EVs use roughly 15–20 kWh per 100km in real-world driving, though this varies with vehicle size, driving style, speed, and climate (cold weather reduces efficiency). This calculator's default of 3.5 miles/kWh corresponds to about 17.8 kWh/100km, a reasonable mid-range figure.
- How does battery degradation affect the calculation?
- This calculator assumes constant efficiency over the ownership period and does not model battery degradation, which typically reduces usable range and efficiency gradually over years of use and charge cycles. For a longer ownership horizon, real running costs may rise modestly over time as the battery ages, though most modern EV batteries retain the large majority of their capacity for many years.