Off-peak EV charging: compare the whole bill, not just the night rate

Choose the right off-peak EV tariff comparison

A fixed off-peak window, a supplier-managed charging schedule and a dynamic tariff are different arrangements. In the first, you plan around stated lower-price hours. In the second, a supplier may schedule supported equipment under its product conditions. With dynamic pricing, the applicable unit rate changes over dated intervals rather than being represented by one permanent “night price”.

Octopus Energy’s EV tariff options (such as Intelligent Octopus Go) describe different smart-charging products and eligibility requirements. Use them as an example of why the product name and current conditions matter; do not transfer one product’s charging window, supported hardware or billing treatment to another. Before comparing, write down the exact tariff, region and version of the terms you have checked.

References: Octopus Energy — EV tariffs and eligibility

Collect a full set of inputs

Find your annual household electricity use and establish whether that total already includes the EV. If it does, do not add the full EV estimate on top again. For a new EV, estimate annual mileage, miles per battery kWh, home charging share and charging efficiency. Keep workplace and public charging out of the home bill and account for them separately where relevant.

For each tariff, collect VAT-inclusive unit prices, daily standing charge, applicable hours and contractual conditions such as exit fees. Ofgem’s consumer energy guidance provides useful background for reading unit rates and standing charges on a bill. Use your own tariff documents for the numbers; a national headline or an old screenshot is not a complete quotation for your property.

References: Ofgem — Understanding unit rates and standing charges

Give the EV and the household different off-peak shares

The car may be able to wait for cheaper hours, while cooking, lighting and other household demand follow a different routine. Our EV tariff calculator therefore asks for separate off-peak percentages. Setting both to 100% without evidence will usually describe an idealised schedule, not the household you are trying to model.

If you have consumption history, use it to estimate a plausible split across the proposed window. Otherwise compare a cautious scenario with an optimistic one. Moving some usage may be convenient; moving every activity may not be. The purpose is to expose how much the result depends on behaviour, not to persuade you that an inconvenient schedule is automatically worthwhile.

A worked whole-bill comparison

Consider an entirely hypothetical household using 3,000kWh a year outside the EV, plus 2,500kWh of home EV grid electricity. Tariff A charges a flat £0.25/kWh with a £0.50 daily standing charge. Tariff B charges £0.10 off-peak and £0.30 at other times, with the same standing charge. Assume all EV charging and 20% of other household use fall off-peak.

Tariff A costs 5,500 × £0.25 + 365 × £0.50 = £1,557.50. For Tariff B, EV electricity costs £250, household electricity costs £780, and standing charges add £182.50: total £1,212.50. The modelled saving is £345. These are constructed scenarios, not live offers, and the result depends on every assumption being appropriate.

Check how fragile the saving is

Keep the previous example but suppose only half the EV electricity is charged off-peak. The EV component on Tariff B becomes £500, taking the annual total to £1,462.50. The saving falls to £95. A change in charging timing has used up £250 of the apparent benefit, without any change to the advertised low rate.

Now return to all EV use being off-peak but raise the hypothetical peak price from £0.30 to £0.40. The 2,400kWh of peak household use adds another £240 a year, reducing the original saving from £345 to £105. These comparisons show why household daytime demand and charging flexibility deserve as much attention as the night rate.

Make sure the car can receive enough energy in time

A tariff window has a physical charging limit as well as a financial one. At a constant 7kW input for four hours, the grid provides 28kWh. Assuming 90% efficiency, 25.2kWh reaches the battery. If your required top-up is 36kWh, it will not fit entirely into that example window at that input power.

Check vehicle AC capacity, charger power and any property restriction in our charging-time calculator or read our guide on 7kW vs 22kW charging speeds. Leave room for interruptions and confirm how the supplier treats charging outside the nominal window. A supplier-managed tariff may have specific arrangements; follow its actual terms rather than assuming an ordinary timer reproduces them.

Treat dynamic tariffs as a separate calculation

A dynamic tariff needs prices matched to the times at which energy is consumed. Averaging published prices without weighting by your charging consumption can give a misleading result. A cheap interval does not reduce your bill if you were not consuming electricity in it, while an expensive interval can matter greatly if it coincides with a large load.

The Octopus Energy public API exposes dated rate information. Our adapter can retrieve and validate such intervals, but the public two-rate calculator does not forecast future prices or optimise a charging schedule. Use a consistent period and timestamped consumption for an interval-based comparison. Do not describe a historical best-case calculation as guaranteed future savings.

References: Octopus Energy — Public electricity tariff API

What to verify before switching

Check eligibility for your meter, vehicle and charger with the supplier, as well as the contract dates, billing method and any exit fee. Save the tariff documents that support your calculation. If the offer depends on a particular integration, confirm your exact equipment using our verified charger selector.

Run the annual comparison with realistic off-peak shares and then a less favourable scenario. Explore our comprehensive guide on home EV charging costs to understand your baseline cost per mile before making any contract commitment.