Cost to charge an electric car: the UK calculator

Pick your car, your mileage and your tariff. Get your real annual charging cost, the cost per mile, and how it stacks up against petrol, with the saving from switching to a smart tariff worked out from your own numbers rather than a marketing average. No email, no sign-up.

What charging actually costs, and what drives it

The honest answer to “what does it cost to charge an electric car?” is that it depends far more on when you charge than on what you drive. The car matters less than most people expect. The tariff matters more.

Three numbers decide your annual cost. How much energy your car uses, measured in miles per kWh (its efficiency). How far you drive in a year. And what you pay for a unit of electricity, in pence per kWh. Multiply them through and you have the figure: annual mileage, divided by efficiency, times your unit rate. The calculator above does exactly that, then puts it next to petrol.

A quick word on efficiency, because it is the one people guess wrong. A small, aerodynamic EV will return well over 4 miles per kWh; a large SUV in winter might manage 2.5. Most cars sit somewhere around 3.5 to 4 miles per kWh in real-world use, which is a little worse than the official WLTP figure. The tool uses each car’s own number from our vehicle data, or you can enter your own if you track it. Battery size, despite being the headline spec everyone quotes, barely matters for running cost. A bigger battery means a longer time plugged in, not a higher cost per mile.

Two things move efficiency more than the car you pick. Cold weather is the big one: a winter morning can knock 20 to 30 per cent off your range while the battery and cabin warm up, which means a winter mile costs more than a summer one. Speed is the other: steady town and A-road driving is gentle on an EV, while sustained motorway speed is where the numbers fall away fastest, the opposite of a diesel. If your driving is mostly long motorway runs, assume the lower end of the efficiency range; if it is mostly local, the higher end.

The tariff is the biggest lever by a distance

Here is the part that changes the answer completely. The single largest factor in your charging cost is the unit rate, and the unit rate is set by your tariff, not your car.

On a standard variable tariff, the rate is capped by Ofgem and sits at about 26p per kWh from 1 July 2026 (24.67p until the end of June). On a dedicated smart EV tariff such as Intelligent Octopus Go, you charge overnight at 8p per kWh. That is the same electricity, for roughly a third of the price, for doing nothing more than plugging in at night and letting the tariff schedule the charge.

Put real numbers on it. Take a typical EV doing around 3.7 miles per kWh over 8,000 miles a year. That needs roughly 2,160 kWh of electricity. On a standard variable rate of 26p, that is about £565 a year, or 7p a mile. On Intelligent Octopus Go at 8p, the same driving costs about £173 a year, or just over 2p a mile. The difference, for identical mileage in the identical car, is close to £390 a year. The only thing that changed was the tariff.

That gap is the whole reason the calculator defaults to a smart tariff and then shows you what you would pay on it versus your current rate. Whenever the saving appears, it is worked out from your own mileage and rate, not a marketing average, so treat it as a personal estimate rather than a promise. If switching looks worthwhile on your numbers, our guide to the best EV tariffs is the next step.

One honest caveat on the smart-tariff rate. Tariffs like Intelligent Octopus Go need a compatible car or charger to deliver the cheapest, automatically scheduled charging, and most newer EVs and smart chargers qualify. If yours does not, a simpler fixed-window tariff (a flat overnight rate, no scheduling intelligence) still gets you most of the saving, just without the smart dispatch. Either way the lever is the same: a cheap overnight rate is what cuts the bill, and the calculator lets you model any of them, or your own rate, rather than assuming everyone is on the headline tariff.

How the petrol comparison works

The petrol figure is the one that tends to land hardest, so we are careful to show the working rather than flatter the EV.

A petrol car’s fuel cost per mile is the pump price divided by its real-world economy, converted from gallons to litres. We assume a comparable petrol car returning around 45mpg in real use, and we use the official UK weekly petrol price (the gov.uk average) rather than baking in a flattering number. At the time of writing that price is around 158p a litre, and it moves week to week, so the petrol comparison in the tool updates with it.

Carry the same example through. Eight thousand miles at 45mpg burns about 808 litres of petrol. At around 158p that is roughly £1,275 a year, or about 16p a mile. Against the smart-tariff EV cost of around £173, that is a difference of over £1,100 a year on fuel alone. Even against the standard-rate EV figure, petrol still costs more than twice as much per mile. The headline holds, but notice how much of the EV’s advantage comes from the tariff rather than from the car simply being electric.

Two honest caveats. This tool compares energy and fuel only. It does not fold in servicing, insurance or tax differences between the two, which cut both ways and deserve their own treatment. For the tax side, our road tax checker covers what an EV now pays in VED, and the company-car tax calculator covers salary-sacrifice running costs. And because the petrol price genuinely swings week to week, the petrol saving is the least stable number on the page. We would rather show you a real, moving figure than a tidy fixed one that is quietly wrong.

What about public charging?

This calculator assumes you charge at home, because for most owners that is where the vast majority of charging happens and where the cost is lowest. Public charging is a different and much pricier picture, and it is worth knowing the gap.

Public rapid and ultra-rapid chargers, the ones you use on a long trip, typically cost somewhere around 70p to 85p per kWh, several times the home off-peak rate and often more than petrol per mile once you account for it. Slower public chargers, the destination units at supermarkets and car parks, sit lower but still well above a home smart tariff. The practical upshot is that an EV’s running-cost advantage is largely a home-charging advantage. If you can charge at home overnight, the numbers in this tool are realistic. If you would rely heavily on public rapids, your real cost would be far higher, and the honest version of that is to enter a blended rate in the custom field that reflects your actual mix of home and public charging.

You will notice the calculator does not ask where you live, and that is deliberate.

Electricity unit rates vary by region (the UK is split into 14 distribution areas) and they change every three months when Ofgem resets the cap. Building a tool that claims postcode-level precision means maintaining a regional rate dataset that is out of date within a quarter, and precision that decays that fast is just inaccuracy with extra confidence. So we default to representative national and tariff rates, which are accurate enough for the decision this tool is actually for: is a smart tariff worth switching to, and how does running an EV compare to filling up.

If you want an exact figure for your own situation, the custom rate field is the answer. Take the off-peak unit rate straight off your latest bill or your tariff page, type it in, and the calculator runs on your real number instead of our representative one. That is more accurate than any postcode lookup we could maintain, because it comes from your actual account.

What the tool counts, and what it leaves out

The calculator shows the cost of the electricity used to charge the car. It excludes the daily standing charge, because you pay that to be connected to the grid whether or not you own an EV, so attributing it to the car would overstate what the car actually costs to run.

It also assumes you charge in the cheap window. That is the point of a smart tariff, and for most home chargers it happens automatically overnight. In reality, if some of your charging spills into peak hours, or you top up on pricier public chargers, your true cost sits between the off-peak figure and the standard rate. The custom rate field is the honest way to model that: enter a blended rate that reflects how you actually charge.

The bottom line

The cost of running an electric car is, more than anything, a tariff question. The car you choose nudges the number; the tariff you are on can roughly halve it or double it. If you are charging at home on a standard variable rate, moving to a smart EV tariff is usually the single biggest saving available to you, and it is worth far more than agonising over which charger to buy. Run your own numbers above, then see the best EV tariffs to find the one that fits.

How this calculator works

We work out your annual charging cost as annual mileage ÷ your car’s efficiency (miles per kWh) × your unit rate. That gives the cost of the electricity used to charge, on the tariff you pick or a rate you type in yourself. We then run the same mileage on Intelligent Octopus Go (a smart overnight tariff at 8p/kWh) so you can see the saving from switching, and against an equivalent petrol car using the official UK weekly petrol price. Every saving shown is worked out from your own inputs, so treat it as an estimate, not a guaranteed figure.

Assumptions

• Electricity rates come from our maintained 2026 UK tariff data. The standard variable rate is Ofgem’s price-cap unit rate (24.67p/kWh to 30 June 2026, then 26.11p/kWh from 1 July 2026; GB average, Direct Debit, incl. VAT). Intelligent Octopus Go is 8p/kWh off-peak.
• Efficiency is each car’s real-world figure, drawn from EV Database consumption data and a little below the official WLTP number. Choose “Enter efficiency manually” to use your own; most EVs sit around 3.5–4 miles per kWh.
• The standing charge is excluded. You pay the daily standing charge to be connected to the grid whether or not you own an EV, so attributing it to the car would overstate its running cost. The figure shown is the electricity used to charge. (Our EV tariffs comparison takes the opposite scope: it includes the standing charge to answer “your total annual cost on this tariff”, so the two tools will differ for the same inputs, by design.)
• The petrol comparison assumes a comparable car at about 45mpg and uses the official UK weekly petrol price (around 158p/litre at the time of writing). It covers fuel and energy only, not servicing, insurance or tax differences.
• No regional precision. Rates vary by region and change quarterly, so we use representative national and tariff rates. For an exact figure, use the custom-rate field with the off-peak rate from your own bill.