EV vs. Petrol/Diesel Cost Calculator
Compares the yearly energy cost of an electric vehicle with a petrol or diesel car from yearly distance, each car's efficiency and local prices. Electricity is priced at a blend of home and public charging rates and divided by a charging efficiency, since a car's display leaves out charging losses. Fuel follows litres per 100 km or mpg. The yearly saving, taken from the figures as shown, divides into the EV's extra price to give a payback in years.
Enter how far you drive in a year, how much energy the electric car uses, what you pay for electricity at home and at public chargers, and the petrol or diesel car's fuel use and pump price. The calculator returns what each car costs to run for a year, the yearly saving, and how long that saving takes to repay an EV's higher purchase price. A table shows the same comparison if every charge happened at home or at public chargers, which is often the difference between a large saving and none. Metric, US and UK units are supported, and prices take your own currency.
How the comparison is worked out
Each car gets a running cost per kilometre or mile, which is then multiplied by the yearly distance. For the EV, the energy figure is divided by the charging efficiency, because some electricity is lost between the socket and the battery, and then priced at a blend of the home and public rates.
EV cost per km = kWh per km ÷ charging efficiency × (home price × (1 − public share) + public price × public share)
fuel cost per km = L/100km ÷ 100 × fuel price
payback years = extra price ÷ (fuel cost per year − EV cost per year)
Take the metric defaults: 15,000 km a year, an EV using 17 kWh per 100 km, 90% charging efficiency, and a fifth of the charging done at public chargers. The blended price is 0.25 × 0.8 + 0.60 × 0.2 = 0.32 per kWh. Charging losses lift the 17 kWh to 17 ÷ 0.9 = 18.89 kWh drawn from the grid for every 100 km, which costs 6.04, or 907 over the year. The petrol or diesel car at 7.2 L/100km and 1.85 a litre costs 13.32 per 100 km and 1,998 a year. The EV saves 1,998 − 907 = 1,091 a year, so an EV costing 5,000 more repays the difference in 5,000 ÷ 1,091 = 4.6 years.
The saving is taken from the two yearly figures as they are shown, and the payback divides the extra price by that saving, so both can be checked against the screen. US mode prices fuel per US gallon and takes the EV's use in kWh per 100 miles, the unit on the American window sticker. UK mode takes miles per kWh and UK mpg, converts imperial gallons at 4.54609 litres, and prices fuel by the litre. In every mode the fuel side gives the same cost per kilometre or mile as the fuel cost calculator. Leave the extra price blank to compare running costs alone, or enter 0 if the EV costs no more to buy.
Reading an EV's efficiency figure
Electric cars are rated in three ways. European specifications quote kWh per 100 km, the US label quotes kWh per 100 miles, and British drivers often see miles per kWh. To turn miles per kWh into kWh per 100 km, divide 62.137 by it, so 3.5 mi/kWh is 17.75 kWh/100km. The US label's headline MPGe converts too: the EPA's 2011 label rule counts one gallon of gasoline as 33.705 kWh, so kWh per 100 miles is 3,370.5 divided by the MPGe figure.
The harder question is where the energy was measured. The same rule explains that an electric car's figure is the energy needed to recharge the battery after the test, "as measured at the electrical outlet; thus, it includes the energy used to propel the vehicle as well as charging losses." Europe's WLTP regulation does the same: its meter is "placed between the vehicle charger and the mains", and the consumption is the recharged energy divided by the electric range. With either figure, set the charging efficiency to 100%.
A car's own display counts the energy leaving the battery, so it leaves those losses out. Fueleconomy.gov, run by the US Department of Energy and the EPA, puts battery charging efficiency at 84% to 93%, which is why the default is 90%. Rapid DC chargers bypass the car's on-board charger, so applying one efficiency to every kWh slightly overstates what public charging costs.
Where you charge decides the answer
Home electricity and public rapid charging are priced very differently, and the table shows how much that matters. At the metric defaults, charging only at home costs 4.72 per 100 km, or 708 a year, while charging only in public costs 11.33 per 100 km, or 1,700. The petrol or diesel car still costs more at 1,998, but the margin shrinks from 1,290 to 298.
In US mode the defaults reverse the result. Charging only in public at 0.45 per kWh costs 1,400 a year against 1,078 for gas, so a driver with nowhere to plug in at home would pay more than for gasoline. The cheapest row is highlighted unless two rows show the same costs, and the mix row is left out when everything is charged in one place.
How the electric car came back into the comparison
The comparison is older than it looks. Around 1900 electric cars were popular with city drivers. The US Department of Energy's history of the electric car notes that they were "quiet, easy to drive and didn't emit a smelly pollutant", while gasoline cars "needed to be started with a hand crank". They lost on price and range. By 1912, the same history records, a gasoline car cost $650 while an electric roadster sold for $1,750, and that year Charles Kettering introduced the electric starter, first fitted to Cadillacs, which did away with the crank. Cheap Texas crude did the rest, and electric vehicles had all but disappeared by 1935.
The oil shocks of the 1970s brought them back into policy. On 13 September 1976 President Gerald Ford vetoed the Electric and Hybrid Vehicle Research, Development, and Demonstration Act, calling its five-year, $160 million program, including some 7,500 demonstration vehicles bought by the federal government, premature and wasteful. The House overrode the veto on 16 September and the Senate on 17 September, and the bill became Public Law 94-413.
Modern electric cars reached American buyers in late 2010, when the Nissan LEAF and the plug-in Chevrolet Volt went on sale. The EPA and the National Highway Traffic Safety Administration then redesigned the window sticker in a rule published on 6 July 2011, required from the 2013 model year and optional for 2012. Electric cars gained an MPGe rating and a consumption figure in kilowatt-hours per 100 miles, the figure this calculator asks for in US mode. From it, the cost of a mile is a multiplication by the price of a kWh.
What the comparison leaves out
It compares energy only. Servicing, tyres, insurance, road tax, depreciation and the cost of fitting a home charger all sit outside the figures, as do grants and tax incentives unless you take them off the extra price. Standing charges are left out because you pay them whether or not you charge a car. The home price should be your average rate, so a cheaper overnight tariff counts only if you enter it. Cold weather raises an EV's consumption, so a yearly average from the display is a better input than a summer reading. Fuel and electricity prices move quickly, so enter what you pay today.
Results are estimates from a simplified yearly model, not a quote or financial advice. See the site disclaimer.
Frequently asked questions
Is an electric car cheaper to run than a petrol or diesel car?
Usually, when most of the charging happens at home. At the metric defaults, 15,000 km a year at 17 kWh per 100 km costs 907 in electricity against 1,998 in fuel for a car using 7.2 L/100km at 1.85 a litre, a saving of 1,091. Public charging narrows the gap: charged only in public at 0.60 per kWh, the same EV costs 1,700. In US mode, public-only charging at 0.45 per kWh costs 1,400 a year against 1,078 for gas.
Do EPA and WLTP figures include charging losses?
Yes. The EPA measures the energy needed to recharge the battery after its test at the electrical outlet, and the EU's WLTP rules place the meter between the vehicle charger and the mains, so both figures already count the electricity lost while charging. Set the charging efficiency to 100% when you enter either one. A car's own display counts only the energy leaving the battery, and fueleconomy.gov puts charging efficiency at 84% to 93%, so 90% suits a display reading.
How do I convert mi/kWh or MPGe to kWh per 100 km or miles?
Divide 62.137 by miles per kWh to get kWh per 100 km, so 3.5 mi/kWh is 17.75 kWh/100km. For MPGe, divide 3,370.5 by the MPGe figure to get kWh per 100 miles, because the EPA counts one gallon of gasoline as 33.705 kWh. A car rated 120 MPGe uses 28.09 kWh per 100 miles.
How long does an EV take to pay back its higher price?
Divide the extra price by the yearly saving. At the metric defaults, a 5,000 gap and a 1,091 saving give 4.6 years. In US mode the defaults save 375 a year, so the same gap takes 13.3 years. If the EV costs no less to run, the calculator says it never pays back at those running costs. Leave the extra price blank to compare running costs alone.
What does the comparison leave out?
Everything except energy: servicing, tyres, insurance, road tax, depreciation and the cost of fitting a home charger. Grants and tax incentives count only if you take them off the extra price. Standing charges are left out because you pay them whether or not you charge a car, and the extra energy an EV uses in cold weather counts only if your figure includes it.
Sources
- Revisions and Additions to Motor Vehicle Fuel Economy Label (76 FR 39478), EPA and NHTSA, Federal Register, 2011
- All-Electric Vehicles, fueleconomy.gov, U.S. Department of Energy and U.S. Environmental Protection Agency
- NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically, National Institute of Standards and Technology
- The History of the Electric Car, U.S. Department of Energy, 2014
- Veto of the Electric and Hybrid Vehicle Research, Development and Demonstration Bill, The American Presidency Project, UC Santa Barbara, 1976
- Public Law 94-413, Electric and Hybrid Vehicle Research, Development, and Demonstration Act of 1976, U.S. Government Publishing Office, 1976