An electric car that costs $10,000 more than its petrol equivalent breaks even after 8.6 years at 12,000 miles a year — and never breaks even at all if you charge it mostly at public fast chargers. Both facts fall out of one small model, and the second one is the reason "EVs are cheaper to run" needs a qualifier.

The sticker price is the worst way to compare two cars. What matters is total cost of ownership: purchase price plus everything you pay to keep the car moving over the years you own it. The model is simple enough to fit in one function, and the interesting part is not the function — it is which inputs actually move the answer.

The model 

function annualCost({ miles, fuelPerMile, maintenance }) { return miles * fuelPerMile + maintenance; } function totalCost({ price, years, miles, fuelPerMile, maintenance }) { return price + years * annualCost({ miles, fuelPerMile, maintenance }); }

Fuel cost per mile is where the two cars diverge:

  • EV: electricity price ÷ efficiency. At $0.16 per kWh and 3.5 miles per kWh: $0.16 / 3.5 = $0.0457 per mile.
  • Petrol: fuel price ÷ fuel economy. At $3.50 per gallon and 32 mpg: $3.50 / 32 = $0.1094 per mile.

Per mile, the EV costs less than half as much to fuel. That is the headline — and it is also where most comparisons stop, which is why they mislead.

Worked example: $38,000 EV vs. $28,000 petrol car, 12,000 miles a year

  • EV fuel: 12,000 × $0.0457 = $548.57 a year
  • Petrol fuel: 12,000 × $0.1094 = $1,312.50 a year
  • Fuel saving: $763.93 a year
  • Maintenance (illustrative): EV $300 a year vs. petrol $700 a year — no oil changes, fewer brake jobs thanks to regenerative braking, but tyres wear faster on a heavier car. Saving: $400 a year
  • Total annual saving: $1,163.93

Against a $10,000 purchase-price gap, break-even is $10,000 / $1,163.93 = 8.59 years — about 103,100 miles.

The year-by-year totals make the shape clear:

  • After 5 years: EV $42,242.86 vs. petrol $38,062.50 — the EV is still $4,180.36 more expensive
  • After 8 years: EV $44,788.57 vs. petrol $44,100.00 — nearly tied, EV still $688.57 behind
  • After 10 years: EV $46,485.71 vs. petrol $48,125.00 — the EV is finally $1,639.29 cheaper

So the honest answer to "is an EV cheaper?" is: not for the first eight and a half years, at these prices and this mileage. If you sell at year five, you paid a premium for the privilege. The savings are real but back-loaded — the exact opposite of how a purchase decision feels in the showroom.

The figure that surprised me: fast charging erases the fuel advantage entirely

All of the above assumes home charging at $0.16 per kWh. Charge mostly at public DC fast chargers at $0.50 per kWh and the EV's fuel cost becomes $0.50 / 3.5 = $0.1429 per mile — $1,714.29 a year, which is $401.79 a year more than the petrol car's fuel bill.

The car did not change. The charger did. An EV charged at home costs $0.0457 a mile; the same EV charged on the motorway costs $0.1429 a mile — more than triple, and more expensive per mile than petrol. Anyone without home charging who runs the "EVs are cheap to run" numbers using a home electricity tariff is modeling a life they do not live.

Mileage matters just as much. Halve the driving to 6,000 miles a year and the annual saving falls to $781.96, pushing break-even out to 12.79 years — beyond how long many people keep a car. Double the petrol price to $5.00 a gallon and break-even pulls in to 5.79 years. The answer is never "EVs win" or "petrol wins"; it is a break-even point that moves with four inputs — electricity price, fuel price, mileage, and the purchase gap — and the only honest comparison is the one that shows that point moving.

Honest caveats

  • This model excludes financing, insurance, tax credits, and resale value. A tax credit shrinks the purchase gap directly; a higher resale value for one car shifts the totals at sale time. Both can move break-even by years — include them if they apply to you.
  • Electricity and fuel prices are local and volatile. Home tariffs, time-of-use rates, and petrol prices vary by region and year. The figures here are illustrative US-style inputs, not quotes.
  • Battery replacement is the tail risk, not the base case. Most EV batteries are warrantied for 8 years or 100,000 miles, and degradation is gradual, not a cliff. But an out-of-warranty replacement is a five-figure bill that would rewrite this model — it is a risk to price, not a certainty to assume.
  • Maintenance figures are averages, not promises. Tyre costs, repair rates, and service prices vary by model. Treat the $400 annual maintenance gap as a starting assumption to replace with your own car's numbers.
  • Efficiency varies with weather and driving. Cold weather, motorway speeds, and heating cut EV efficiency; short cold-start trips hurt petrol economy. Real-world numbers beat brochure numbers for both.

Run your own numbers

Put in your cars' prices, your electricity and fuel prices, your mileage, and your charging mix — home, public, or both — and see your own break-even point:

EV vs. petrol calculator — free, no signup, runs entirely in your browser.

The sticker price is a single number. Ownership is a curve — and the curve crosses later than the brochure suggests.