Annual non-EV electricity
A high daytime household load makes an expensive peak rate more important.
How to compare an EV tariff properly
The cheapest overnight charging rate can be misleading if the tariff raises the price of the electricity your home uses during the day. The right comparison is the annual cost of the whole household.
Reviewed 20 September 2026UK units unless statedCalculations and assumptions shown
Compare both tariffs over a full year
Annual tariff cost = peak kWh × peak rate + off-peak kWh × off-peak rate + 365 × standing charge
For a flat tariff, all unit consumption uses one rate. For an EV tariff, split consumption according to what can realistically move into the off-peak window.
Worked example: whole-home tariff comparison
Use 3,200 household kWh, 8,000 EV miles/year, 3.5 miles/kWh at the battery and 90% charging efficiency. EV grid energy is 2,539.68 kWh. No non-EV household electricity moves off-peak. Compare 26p/kWh flat with 31p peak and 8p off-peak, both with 50p/day standing charges. The flat-tariff total is £1,674.82/year.
| EV charging off-peak | EV tariff annual cost | Saving vs flat |
|---|---|---|
| 60% | £1,611.33 | £63.49 |
| 80% | £1,494.50 | £180.32 |
| 95% | £1,406.88 | £267.94 |
The EV tariff matches the flat tariff at 49.13% off-peak EV charging. Above that share it is cheaper under these assumptions. Rates are illustrative and are not an available offer. The calculator also lets you move a separate share of household electricity into the cheap window.
The inputs that matter most
EV mileage and efficiency
More annual charging gives the cheap window more opportunity to offset a higher daytime rate.
Off-peak capture
Do not assume 100% unless your actual schedule makes that realistic.
Standing charge
A few pence per day becomes a meaningful annual difference.
Use scenarios instead of one optimistic forecast
Run the comparison at, for example, 60%, 80% and 95% off-peak charging. Then vary annual mileage or household electricity. If the same tariff wins across all plausible scenarios, the decision is more robust. If a small assumption flips the answer, treat the result as a close call rather than a precise saving.
What a robust result looks like
If the EV tariff only wins when 100% of charging lands in the cheap window and household use is unusually low, the saving is fragile. If it still wins when you reduce off-peak capture, increase daytime use and include the higher standing charge, the conclusion is more resilient. Save or note the assumptions you used so you can compare them with a real bill later.
Tariff terms can change. Re-run the calculation with the rates and standing charges actually offered to you rather than relying on an old example from a forum, video or comparison article.