EV tariffs explained: the off-peak window that changes the maths
The cheapest EV charging tariff we track today is Octopus Go off-peak (London example) at 8.6p/kWh off-peak — a full charge of an average 62 kWh electric car costs about £6.11 on it, against £18.50 at the July 2026 Ofgem price cap (26.11p/kWh). That saving is real, but it is paid for by a higher daytime rate, so it only works if enough of your charging happens inside the window. Both sides of that trade are priced below.
Prices based on the Ofgem price cap of 26.11 p/kWh, effective 1 July 2026.Source: Ofgem
The break-even: how much of your charging must happen in the window
This is the number that decides whether an EV tariff is worth it, and it is almost never published. Suppliers do not expose their daytime rates through any public API, so the day rates below are assumptions — a premium over the July 2026 cap of 26.11p/kWh. The break-even for each one is exact arithmetic: (day rate − cap) ÷ (day rate − off-peak rate), using Octopus Go off-peak (London example) at 8.6p/kWh.
| Assumed day rate | Premium over the cap | Share of charging needed in the window to break even |
|---|---|---|
| 28.11p/kWh | +2p | 10% |
| 30.11p/kWh | +4p | 19% |
| 32.11p/kWh | +6p | 26% |
Read it this way: on a tariff whose day rate sits 2p above the cap, you need only 10%of your electricity to land in the off-peak window before you are ahead — and everything beyond that is profit. The figures assume all household electricity, not just the car; if you can shift laundry and dishwashing into the window too, you clear the bar sooner.
EV tariff comparison: the same charge, and the same year, on each tariff
The comparison that matters is the last column: what a year of driving costs on each tariff, for the average EV we track at 10,000 miles with every charge inside the cheap window. Against the price cap, Octopus Go off-peak (London example) saves £443.35 a year on that basis.
| Tariff | Unit rate | Full charge, average EV (62 kWh) | Pence per mile (average EV) | Per year, 10,000 miles |
|---|---|---|---|---|
| Ofgem price cap | 26.11p/kWh | £18.50 | 6.6p | £662.05 |
| Octopus Go off-peak (London example) | 8.63p/kWh | £6.11 | 2.2p | £218.70 |
Octopus rates fetched live from their public API (London region example; rates vary by region — see costs by region). “Average EV” is the mean of the 50 models we track, losses included. Off-peak figures assume all charging happens inside the cheap window.
How the window actually works
A few hours, usually after midnight
Go-style tariffs publish a fixed overnight window of around five hours. You schedule the car (or the charger) to draw power only then. A 7 kW wallbox can add roughly 35 kWh inside a five-hour window — most of most batteries.
“Intelligent” tariffs flex the window
Smart variants control your charging session themselves and can extend cheap hours beyond the advertised window when the grid is quiet — usually the cheapest option of all if your car or charger is compatible.
The day rate is the catch
EV tariffs typically price daytime electricity above the price cap level — for the whole house, not just the car. Heavy daytime users with modest mileage can end up worse off. The break-even depends on your mileage and daytime consumption; our calculator lets you test your own numbers.
Three-pin owners rarely benefit fully
At 2.3 kW, a five-hour window only adds ~11 kWh. If you rely on a three-pin plug, you may not fit a useful charge inside the cheap hours — see the three-pin guide.
10,000 miles on the price cap
£662.05
average EV, home charging
Same miles, cheapest off-peak window
£218.70
if every charge fits the window