EV vs petrol: the honest savings calculator

The honest answer first

For most drivers an electric car is far cheaper to fuel than a petrol or diesel one. Not a little cheaper, a lot: on a smart overnight tariff a typical EV costs roughly 2p a mile against the mid-teens for petrol. Over an average year that is the difference between a few hundred pounds and well over a thousand.

But that headline rests almost entirely on one thing: where you charge. Charge at home on a cheap overnight rate and the saving is enormous. Charge mainly on public rapid chargers and the saving shrinks hard, and for a less efficient car it can disappear altogether. So the honest version of “is an EV cheaper than petrol” is “yes, if you can charge at home, and the calculator above tells you your own number rather than the rosy one”.

That is what this tool is for. Pick your car or enter its efficiency, set your mileage, choose how you charge, and compare it against the petrol or diesel car you would otherwise run, on live UK fuel and electricity prices. It compares the cost of moving the car: the energy or fuel only. We will be clear later about what that leaves out.

The maths, in pence per mile

Pence per mile is the honest unit for this comparison. It strips out how far you happen to drive and leaves the thing that actually differs between two cars: what a mile costs to fuel. Here is the picture at a representative efficient EV (a Tesla Model Y Long Range RWD, around 3.9 real-world miles per kWh) against comparable petrol and diesel cars, on UK prices as of June 2026.

Read it from the top and the story is the charging access, not the car. The same EV costs about 2.1p a mile charged overnight, 6.7p on the standard capped rate, and 20.3p on public rapid. The car never changed. Only the unit rate did. Petrol sits around 15.8p a mile and diesel around 14.6p, so an EV charged at home undercuts both by a wide margin, while the same EV on public rapid alone costs more per mile than either.

Charged overnight at home an EV costs around a seventh of what it costs to fuel on public rapid. The car is identical. The only thing that changed is where the electricity came from.

That public-rapid figure is the one most savings calculators leave out, and it is the one worth stating plainly. On the Zapmap Price Index the weighted-average pay-as-you-go price on rapid and ultra-rapid chargers was 79p per kWh in May 2026, with the major networks spanning roughly 63p to 92p. At that price, an efficient EV run entirely on public rapid is not a cheaper car to fuel than petrol. It is a slightly dearer one. Most owners never live at that end of the scale, because most charging happens at home, but a driver with no home charging realistically does, and they deserve to see it before they buy.

Put a year’s numbers on it

Cost per mile is the clean comparison, but most people think in pounds per year, so here is the same example carried through a typical 8,000 miles. An efficient EV at 3.9 miles per kWh uses about 2,050 kWh to cover that distance. Charged overnight at 8p, that is roughly £164 a year. On the standard capped rate of 26.11p it is about £536. On public rapid at 79p it is about £1,620.

Now the cars it replaces. A 45mpg petrol doing the same 8,000 miles burns about 808 litres, which at around 156p a litre comes to roughly £1,260 a year. A 55mpg diesel burns less fuel but pays more for it, landing close behind at about £1,170.

Line those up and the home-charging saving is roughly £1,100 a year against petrol and a little over £1,000 against diesel. Switch the EV to public rapid only and the arithmetic flips: it now costs about £360 more a year than the petrol car and £450 more than the diesel. Same car, same mileage, opposite verdict. The only variable that moved was the charger. The calculator runs this for your own mileage and car rather than our example.

The home-charging asterisk

Everything good about an EV’s running cost comes from the cheap overnight rate, and the cheap overnight rate assumes two things: a place to charge off-street, and a smart tariff to schedule it. Roughly a third of UK households cannot charge at home, and for them the rosy number simply does not apply. There is no point pretending otherwise.

If you can charge at home, the saving is real and the next question is how to lock in the cheap rate. A dedicated EV tariff with an off-peak window near 8p per kWh is what does the heavy lifting; the standard variable rate, capped by Ofgem at 26.11p per kWh from 1 July 2026, is roughly three times dearer for the identical electricity. Getting onto the right tariff is worth far more than agonising over which charger to buy. Our guide to the best EV tariffs is the place to start, and it is the natural next step once the calculator shows switching is worth it on your numbers.

If you cannot charge at home, be honest with the tool. Use the custom-rate field and enter a blended rate that reflects your real mix of public charging, rather than the home-overnight default. The number it gives back will be higher, and it will be true.

How much public charging before the saving disappears

The public-rapid figure sounds alarming on its own, but very few drivers charge entirely on rapids. The realistic question is not “home or public” but “what mix”, so it is worth knowing where the line actually falls.

An efficient EV stops being cheaper to fuel than a 45mpg petrol car at a blended electricity rate of about 61p per kWh. Below that you are ahead; above it you are behind. Starting from an 8p overnight rate and topping up the rest on 79p public rapid, you would need to do roughly three-quarters of your charging on public rapid before the saving vanished. Against a more efficient 55mpg diesel the line is a little lower, around two-thirds.

Put the other way round, that is reassuring. A driver who charges mostly at home and occasionally rapids on a long trip, which describes most owners, keeps almost all of the saving. Even someone splitting their charging evenly between home and public rapid stays comfortably cheaper per mile than petrol. It is only the driver with no home charging at all, relying on rapids for the bulk of their miles, for whom an EV is not the cheaper car to fuel.

That is the honest shape of it. The saving is large and robust for home chargers, holds up well for mixed charging, and genuinely disappears only at the all-public extreme. If your mix sits somewhere in the middle, the custom-rate field is the way to model it: work out your rough blended rate, or enter the off-peak rate from your bill for the home-charged portion, and the tool gives you your real number rather than either headline.

Petrol or diesel: which does an EV beat by more?

The “electric car vs diesel” question has its own answer, because diesel and petrol behave differently. Diesel costs more per litre at the pump, around 177p against roughly 156p for petrol in mid-June 2026, but a diesel engine travels further on each litre. Net of the two, a modern diesel often costs a touch less per mile than an equivalent petrol car: in our example, about 14.6p against 15.8p. So a diesel is the tougher benchmark of the two.

It is still not close once an EV charges at home. At around 2.1p a mile on a smart overnight tariff, an EV undercuts a 55mpg diesel by roughly 12p a mile and a 45mpg petrol by roughly 14p. The diesel’s efficiency narrows the gap to petrol; it does not come anywhere near closing the gap to home-charged electricity. Where the diesel comparison does get interesting is at the public-rapid end, where the EV’s per-mile cost climbs past both. The toggle in the calculator lets you set the fuel type and the economy of the specific car you are comparing against, so you can run your own diesel rather than ours.

What this comparison leaves out

This is a fuel-versus-energy comparison and nothing more. It answers “what does it cost to move the car”, not “what does it cost to own the car”. Four things sit deliberately outside it.

The daily standing charge is excluded, the same scope as our charging-cost calculator. You pay the standing charge to be connected to the grid whether or not you own an EV, and a petrol car has no equivalent, so folding it in would compare unlike with unlike. Note that our EV-tariffs comparison takes the opposite scope on purpose, because it is answering “your total annual bill on this tariff”, so the two tools will differ for the same inputs by design.

Vehicle tax sits outside too. An EV’s VED position changed in April 2025, and what an electric car now pays is covered in full by our EV road tax guide. Company-car drivers have a separate and usually decisive saving through benefit-in-kind, which our company-car tax calculator works out. And the rest, purchase price, depreciation, insurance and servicing, all cut both ways and deserve their own treatment rather than a thumb on this scale.

How this calculator works

We work out each side’s cost the same honest way. The EV cost is annual mileage divided by the car’s efficiency in miles per kWh, multiplied by your chosen unit rate, which gives the cost of the electricity used to charge on the scenario you pick. The petrol or diesel cost is annual mileage divided by the car’s economy in miles per gallon, converted from gallons to litres, multiplied by the live pump price for that fuel. The annual saving is one subtracted from the other.

The electricity rates come from our maintained 2026 UK tariff data and the pump prices from the official gov.uk weekly fuel statistics, both read live, so the comparison moves with real prices rather than baking in a flattering snapshot. When the saving goes negative, as it can on public rapid, the tool says so in words rather than printing a tidy minus figure. Every result is computed from your own inputs, so treat it as an estimate for your situation, not a promise.

Assumptions

• Electricity rates are drawn live from our 2026 tariff data. The home-overnight figure is a representative smart-tariff off-peak rate near 8p per kWh; the home-standard figure is the Ofgem price-cap unit rate (24.67p per kWh to 30 June 2026, then 26.11p from 1 July; GB average, Direct Debit, incl. VAT). The public-rapid figure is a representative weighted-average pay-as-you-go rate of 79p per kWh (Zapmap Price Index, May 2026; major networks span roughly 63p to 92p). All three are overridable with the custom-rate field.
• EV efficiency is each car’s real-world figure from EV Database consumption data, a little below the official WLTP number. Choose “enter efficiency manually” to use your own; most EVs sit around 3.5 to 4 miles per kWh.
• Petrol and diesel economy default to sensible real-world figures (around 45mpg petrol, 55mpg diesel) and are fully editable. Pump prices are the official gov.uk weekly UK averages and move week to week.
• Scope: fuel and energy only. The daily standing charge is excluded, as are VED, insurance, servicing, depreciation and the purchase-price difference.
• No regional precision. Rates vary by region and reset quarterly, so we use representative national rates. For an exact figure, enter your own off-peak rate from your bill.