Advanced options
Rate boxes: your standard rate, then E7 day, then E7 night. The catch is the E7 DAY rate premium: everything you use in daylight costs MORE, so E7 only wins when enough load genuinely runs in the 7 cheap hours: storage heaters, hot water tanks, EV charging, timed washing. Typical break-even sits around 20-35% night usage: households without night-loading kit rarely get there. Check your actual night % on a smart meter app before switching either way.
What The Economy 7 Calculator Works Out
- Standard tariff: your annual kilowatt-hours multiplied by the single standard unit rate, unit costs only. 2,900 kWh is a typical medium household.
- Economy 7: daytime kWh at the E7 day rate plus night kWh at the E7 night rate. The seven overnight hours price at 12p to 16p against the standard rate (which defaults to the current Ofgem price cap unit rate), but the E7 day rate carries a 2p to 4p premium, so every daylight kettle subsidises the night's discount.
- Verdict and break-even: the cheaper tariff and the saving, plus the night share at which the two tie: (day rate - standard rate) divided by (day rate - night rate). At typical rates the crossover sits around 19% to 25%. Storage-heater and hot-water-tank homes load 40% to 60% into the window; a gas-heated house with a fridge and standby sits at 15% to 25% and rarely gets there.
- Standing charges (advanced): both default to the current Ofgem price cap figure so the basic comparison is unchanged. Enter each tariff's own daily charge, because E7 deals sometimes carry a different one, and the two total-bill cards add 365 days of it to the unit costs.
- Extra kWh you could move to night (advanced): delay-start washing machines, dishwashers, tumble dryers and a timed immersion heater can migrate several hundred kWh a year across the boundary. This moves existing daytime use into the cheap window.
- EV charging and storage heating (advanced): new night-time load added on top of today's use. A nightly 30 kWh to 40 kWh EV charge drags any household past every threshold, though dedicated EV tariffs with deeper night rates now usually beat classic E7 at that game.
- After adding night loads (advanced): the Economy 7 bill including standing charge once the shifted and added kWh are counted, with the new night percentage and the standard tariff bill for the same total use.
- What if rates rise (advanced): applies the same percentage change to all three unit rates. The break-even night share does not move, but the pounds at stake do.
- Monthly difference (advanced): the gap between the two total bills divided by twelve, the figure to compare against the hassle of re-timing the laundry.
- kWh to shift to break even (advanced): how much daytime use would need to move into the seven cheap hours for Economy 7 to match the standard tariff, including standing charges. Beware that the window's clock varies by region and meter, and some run GMT all year.