Which EV tariff is cheapest for your mileage

The cheapest electric vehicle tariff for you is decided by one number: how many kilowatt hours you push through the cheap window each year. Below a certain mileage, any higher daytime rate that pays for that window costs you more than the window saves.

Work it out from your own figures rather than from a comparison table. The whole calculation is four lines, and a worked example runs through it below.

How these tariffs are shaped

Nearly all of them follow the same pattern. A cheap overnight window of a few hours, in exchange for a standard or sometimes elevated rate the rest of the day. The reference points as of August 2026: Intelligent Octopus Go offers up to six hours at 8p per kilowatt hour, against a price-capped standard rate of 26.11p.

They differ on four things worth writing down for each candidate:

1. The off-peak rate and how many hours the window runs.
2. The peak or standard rate that applies the rest of the time. Some price it at or near the cap; others carry a premium, and this term is where superficially similar tariffs diverge.
3. The standing charge.
4. Whether charging is scheduled by you or by the supplier.

That fourth one is the real difference between the smart tariffs and the plain ones, and it is where the cheapest rates live.

The calculation, worked

You need two figures from your own life: annual mileage, and your car’s real efficiency in miles per kilowatt hour from the trip computer. The example household drives 8,000 miles at 3.5 miles per kilowatt hour, uses 3,100 kilowatt hours a year for everything else, and currently pays the capped flat rate.

1. Annual charging demand equals annual miles divided by miles per kilowatt hour, plus roughly a tenth for charging losses: 2,286 plus losses is about 2,500 kilowatt hours from the wall.
2. Off-peak saving equals that demand times the gap between the off-peak rate and the current flat rate: 2,500 times 18.11p is about £453.
3. Daytime penalty equals non-car consumption times any premium on the tariff’s daytime rate. At a 2p premium: 3,100 times 2p is £62. At no premium: nothing.
4. Net: £391 in the premium case, £453 without one. Switch.

Now rerun it at 2,000 miles a year: charging demand about 630 kilowatt hours, off-peak saving £114, and the same £62 penalty leaves £52, before any standing charge difference. One integration hiccup or one habit of daytime top-ups and the margin is gone. That is the shape of the low-mileage trap: the arithmetic does not go negative loudly, it goes marginal quietly.

Why low mileage often loses

Step three applies to everything else in the house: the fridge, the lights, the washing machine, the television. For most households that is a considerably larger volume than the car uses, as the example’s 3,100 against 2,500 shows even for a fairly typical mileage.

So a modest penalty on a large volume can easily exceed a large saving on a small one. The break-even mileage is higher than people expect, and drivers doing a few thousand miles a year are frequently better off on a plain tariff, or on one whose daytime rate carries no premium at all, which brings the choice back to reading term two carefully.

What shifts the answer in your favour

Moving other loads into the window. Dishwasher, washing machine and immersion heater on timers. Every unit moved is charged at the off-peak rate and reduces the volume exposed to the daytime penalty, improving both terms at once.

A battery. Storage lets the whole house draw on cheap overnight electricity during the expensive part of the day: the arbitrage arithmetic runs at roughly 14.7p of net gain per cycled unit on the cited rates. This changes the calculation completely and usually makes a time-of-use tariff worth taking regardless of mileage.

Solar. Generation offsets daytime consumption, which is exactly the volume the higher daytime rate applies to, though mind the interaction with charging strategy: on a cheap overnight window, exporting your surplus and charging the car at 2am usually beats solar-charging it.

Supplier-scheduled charging

The lowest headline rates generally come with the supplier controlling when your car charges, within a window you set. You say you need the car ready by seven with a certain state of charge; they decide when within the night to draw the power.

What you gain is the cheapest rate available and often a cheap rate applied to your whole house during the charging period.

What you give up is precise control, and a dependency: the car, the charger and the supplier’s system all have to talk to each other. When that integration breaks, sessions get missed and units land at the day rate. Check that your specific car and charger combination is on the supplier’s supported list before switching, and check what the tariff does while an integration fault is open, because the answer varies.

Do the sum before switching

Take your annual mileage, your car’s efficiency, your non-car consumption from your bill, and the four figures above for each candidate tariff. Ten minutes of arithmetic settles it, the per-mile comparison puts the result in familiar units, and the answer is specific to your household in a way no league table can be. If solar or a battery is in the picture too, put the whole combination through the ROI calculator with the EV option on, so the tariff, the panels and the storage are judged as the single system they actually are.