Economy 7 calculator: standard tariff or day/night rates?
Enter how much electricity you use in a year and how much of it falls in the seven night hours. The calculator compares both tariffs and shows the night share at which Economy 7 becomes the cheaper choice.
Unit prices times kWh plus the standing charges, over one year. The Economy 7 rates are a supplier's published standard variable rates, averaged over GB regions; yours depend on your region and supplier.
How the tariff comparison works
On a single-rate tariff every kWh costs the same. On Economy 7 the seven night hours are much cheaper and the day hours dearer, so whether it saves money depends on how much of your use you can move to the night. The calculator prices your yearly use on both tariffs and adds each standing charge.
The break-even share is solved directly: the night share at which both yearly bills are equal. Above it Economy 7 is cheaper, below it the standard tariff is. The standard rate is the Ofgem price cap; the Economy 7 rates are the British Gas standard variable rates averaged over regions and marked as an estimate.
Formula
- Standard = kWh × unit price + standing charge
- Economy 7 = kWh × ((1 − night share) × day rate + night share × night rate) + standing charge
- Break-even night share = (kWh × (day rate − unit price) + standing difference) ÷ (kWh × (day rate − night rate))
Frequently asked questions
Who benefits from Economy 7?
Homes with storage heaters, an immersion heater on a timer or an electric car charged overnight, which can move a large part of their use into the night hours. Without that, most homes use too little at night for the cheaper night rate to cover the dearer day rate.
When are the night hours?
Seven hours, usually between about midnight and 8 am. The exact times depend on your meter and region and can shift by an hour with British Summer Time; your supplier will tell you.
How do I find my night share?
If you already have a two-rate meter, divide the night reading by the total over the same period. If not, add up the use of appliances you could run at night.
Is my data sent anywhere?
No. Everything is calculated in your browser.
Economy 7 in numbers: why the break-even is about a third
The calculator opens with a household using 2,700 kWh a year. The standard tariff is the Ofgem price cap: 26.32p per kWh and £200.15 a year in standing charges. Economy 7 uses the British Gas standard variable rates from 1 October 2026, averaged over its 14 regions: 32.21p by day, 14.81p for the seven night hours, and £199.35 a year standing charge.
With these prices, the headline reads: Economy 7 becomes cheaper once at least 33.7% of your use falls in the night hours. The night-share field starts at 29%, which is simply 7 of 24 hours, as if you used electricity evenly round the clock. At that share the standard tariff costs £911 a year and Economy 7 £933, so Economy 7 is about £22 dearer.
Where the 33.7% comes from
Every kWh you use by day on Economy 7 costs 5.89p more than on the standard tariff. Every kWh used at night costs 11.51p less. The standing charges differ by only 80p a year, so they barely count. Economy 7 comes out ahead once the night savings outweigh the day penalty. That happens when the night share reaches 5.89 ÷ (5.89 + 11.51), which is 33.7% when worked from the unrounded rates the calculator uses.
Because the standing charges are so close, the break-even point hardly depends on how much electricity you use. At 3,718 kWh a year it is still 33.7%. What decides the answer is the share, not the size of the bill. The table shows how the Economy 7 bill moves with the night share at 2,700 kWh.
| Night share | Economy 7 a year | Standard tariff a year |
|---|---|---|
| 0% | £1,069 | £911 |
| 29% | £933 | £911 |
| 40% | £881 | £911 |
| 50% | £834 | £911 |
| 60% | £787 | £911 |
The table also shows the risk on the other side. A home that ends up on Economy 7 but uses little at night pays more than on a standard tariff: £158 more a year at a night share of zero. That can happen in a home where storage heaters were taken out but the tariff was never changed.
Finding your real night share
If you already have a two-rate meter, it shows two registers, often labelled “low” and “normal” or “night” and “day”. Take two readings of each, ideally a year apart or at least a few months apart. Divide the night units used by the total units used. A single winter month can mislead, because storage heaters and immersion heaters use more in the cold months. A smart meter shows the same split in your supplier’s app or on your statements.
If you do not have a two-rate meter, estimate what could run at night. The fridge, freezers and standby already run round the clock, so about 29% of their use falls in the night hours anyway. Beyond that, only loads you can put on a timer count: storage heaters, an immersion heater, a dishwasher or washing machine with delay start, an electric car. Use the electricity usage calculator to see how much each of them uses a year, add them up and divide by your total.
Limits of the comparison
Ofgem’s cap files give a benchmark Economy 7 bill but no separate day and night rates, so the rates here come from one large supplier’s published tariff. They are marked as an estimate. Your own rates depend on your region and supplier, and so do the exact night hours. Type in the figures from your bill or tariff sheet: if your day rate is closer to the standard rate, the break-even share falls; if the night rate is higher, it rises.
The cap prices run from 1 October to 31 December 2026. Ofgem notes there is no VAT on electricity from 1 October 2026 to 31 March 2027, which applies to both tariffs. The comparison covers electricity only; any gas you use is billed separately and does not change it.
A heat pump runs whenever the house needs heat, by day as well as by night, so do not assume it moves much of your use into the night hours. If you are thinking of installing one in England or Wales, the government’s Boiler Upgrade Scheme offers a grant towards it; the details are on that page.
Sources: Ofgem price cap rates and standing charges, British Gas standard variable tariff rates, October 2026.