Compare time-of-use electricity tariffs

For each price window, multiply the electricity used in kWh by its price in pence per kWh, then divide by 100 to get pounds. Add all the windows and the daily standing charge for the number of days covered. With a dynamic tariff, do that calculation for every half-hour.

Use prices on the same VAT basis and for the same postcode and payment method. Keep export income separate so it is clear how much you pay for imports and how much you receive for exports. A monthly Direct Debit can include account credit or debt, so it is not necessarily the cost of that month's electricity.

• Energy Saving Trust: rates, standing charges and contract terms

Annual kWh tells you how much electricity you buy, but not which tariff windows it falls into. Half-hourly smart-meter records, where your supplier makes them available, give a much clearer picture. Look for a complete year that reflects your current household, including winter heating, holidays and the days your car is at home.

If you only have an annual total, estimate the share used in each window and compare several plausible patterns. A home occupied all day, an evening-heavy home and a home charging an EV overnight can have the same annual consumption and different bills. Keep estimated timings visible rather than treating them as measured use.

Check gaps and estimated readings. If you already have solar or a battery, import readings describe what you bought from the grid, not all the electricity your appliances used. Keep that distinction when considering changes to the existing system.

• Smart Energy GB: smart meters and flexible electricity use

Focus on sizeable electricity uses that can change time without disrupting daily life. EV charging can be flexible when the car is plugged in for long enough. Hot-water heating or a battery can also provide flexibility, depending on their controls and limits. Cooking, lighting and essential equipment may have much less freedom.

Compare your present routine with changes you would realistically maintain. Do not assume every appliance moves to the cheapest period every day. For heat pumps, preserve comfort and account for any change in efficiency when shifting heating.

• EV: check your required departure time, charger power, charging losses and whether you can override the schedule.
• Heating and hot water: agree suitable schedules with the installer; do not assume all winter heating can fit into an overnight window.
• Appliances: follow their operating instructions and choose times that suit your household.
• Automation: confirm what happens if the internet connection, price feed or device integration stops working.

A battery can buy electricity in a cheaper window and supply the home later. Some energy is lost in charging, storage and conversion, so one kWh bought does not deliver one kWh to appliances. Usable capacity, reserve, charging power and the length of the cheap window limit how much demand can move.

Keep two questions separate: whether a tariff suits a battery you already own, and whether buying a battery is worth its installed price. Include wear, warranties and replacement costs in the second question. A favourable price difference alone does not establish payback.

• Energy Saving Trust: home battery storage

Solar changes the hours when you need to buy electricity. Export payments change the value of keeping solar energy for later. Compare the complete import and export arrangement, including eligibility and whether a particular import tariff affects the export offer available to you.

In Great Britain, the Smart Export Guarantee provides payments for eligible exported generation under suppliers' terms. Confirm the applicable arrangements in Northern Ireland separately. If you plan to export energy from a battery, check whether grid-charged electricity is eligible under the contract.

• Ofgem: Smart Export Guarantee and supplier terms
• Read the solar, battery and inverter sizing guide

Start with the current home on its current tariff. Next compare the same home on an alternative tariff. Then consider changes to usage timing or new equipment. This makes the benefit of each change clearer and prevents tariff savings being counted again as equipment savings.

For a historical bill check, retain the dated current rates if they changed during the year. For a forward-looking comparison, use the current offer or renewal rates for each option over the same assumed usage. Do not mix a past year's actual bill with an unrelated future price period without explaining the difference.

Check winter as well as summer, and test less favourable assumptions. Extra daytime heating, fewer overnight EV charging sessions or a smaller price difference can change which tariff wins. Revisit the comparison after a major change to the household.