How the calculator works it out
The method follows Idaho National Laboratory’s Department of Energy fact sheet Comparing Energy Costs per Mile for Electric and Gasoline-Fueled Vehicles: work out each car’s energy cost for one mile, then scale up to your yearly miles.
Electricity price = home ¢ × (1 − public share) + public ¢ × public share
EV $/mile = kWh/100 mi ÷ 100 × electricity price ÷ 100
Gas $/mile = gas price ÷ MPG
Yearly cost = $/mile × miles per year
Break-even years = extra EV price ÷ yearly savings
Worked example
You drive 15,000 miles a year. The EV uses 30 kWh per 100 miles. You charge at home at 18.3¢ and do 20% of your charging on fast chargers at 45¢, so your average is 0.8 × 18.3 + 0.2 × 45 = 23.64¢ per kWh. The EV costs 0.30 × $0.2364 = 7.1¢ a mile, or $1,063.80 a year.
The gas car gets 30 MPG on $4.35 gas: $4.35 ÷ 30 = 14.5¢ a mile, or $2,175 a year. The EV saves $1,111.20 a year. If it cost $5,000 more to buy, the fuel savings cover that in 5,000 ÷ 1,111.20 = 4.5 years. Gas would have to fall to 0.07092 × 30 = $2.13 a gallon before the two cost the same to run.
Where the numbers come from
- EV energy use: the EPA label’s kWh per 100 miles, on fueleconomy.gov. The EPA explains its electric figures include losses in the charging cable and on-board charger, measured at the wall.
- Home electricity: the default, 18.31¢ per kWh, is the U.S. average residential price for July 2026 in the EIA Electric Power Monthly, Table 5.6.A, which also lists every state. Your bill’s total divided by its kWh gives your real rate, including fees.
- Public charging: 45¢ is only an example. Fast-charging prices vary by network, state and time of day, and some charge per minute instead of per kWh.
- Gas: the default is the U.S. average regular price for the week of October 5, 2026 from the EIA weekly survey.
This compares energy only. Maintenance, insurance, registration fees (some states add a yearly EV fee), incentives and resale value all affect the full cost of owning either car.
Questions people ask
How do I work out what an EV costs per mile?
Multiply the car’s energy use in kWh per mile by your price per kWh. An EV rated 30 kWh/100 mi uses 0.30 kWh a mile; at 18.3 cents a kWh that is 0.30 × 0.183 = 5.5 cents a mile. A gas car is the gas price divided by its MPG: $4.35 ÷ 30 MPG = 14.5 cents a mile.
Where do I find my EV’s kWh per 100 miles?
It is printed on the EPA window sticker and listed for every model on fueleconomy.gov. Use that figure rather than MPGe. The EPA measures electricity from the wall outlet, so normal charging losses are already included.
Why does public charging change the answer so much?
Fast chargers usually cost more per kWh than home electricity, and prices vary by network, location and time of day. A driver who charges at home overnight pays far less per mile than one who relies on fast chargers. Set the public share to match how you actually charge.
What does break-even mean here?
If the EV costs more to buy than the gas car, break-even is how many years of fuel savings it takes to cover that difference: extra price ÷ yearly savings. It ignores insurance, maintenance, tax credits, financing and resale value, so treat it as one input, not the whole decision.
What gas price makes the two cost the same?
The parity price is the EV’s cost per mile times the gas car’s MPG. If gas is above it, the EV is cheaper to fuel. With the defaults here (23.6 cents a kWh blended, 30 kWh/100 mi, 30 MPG) it is about $2.13 a gallon.