Economy 7 Savings Calculator
Compare an Economy 7 electricity tariff with a single-rate tariff. Enter day and night unit rates, standing charges and the share of electricity you can genuinely move to the cheaper night period.
Tariff and Usage Inputs
Economy 7 Difference
The estimate compares annual Economy 7 cost with annual single-rate cost using your night-use share.
This result is driven by your night-use share. The saving can disappear if the cheap rate is not used enough, so the break-even line is just as important as the headline saving or extra cost.
When Economy 7 Can Work
Night-heavy homes
Storage heaters, immersion heaters, EV charging and appliances on timers can make a higher night share realistic.
Day-heavy homes
If cooking, washing, heating and working from home happen mostly in the day, a high day rate can wipe out the night saving.
Meter timing
Economy 7 hours are set by tariff, meter and region. The cheap period is not always midnight to 7am.
How to Use the Calculator
Use annual electricity consumption from a bill or smart meter statement. If you only know monthly consumption, multiply a typical month by 12, but adjust for electric heating if winter use is much higher. Enter the night share you can realistically achieve. Storage heating and hot water can create a high night share. A household with gas heating, daytime cooking and home working may have a low night share even if it runs a dishwasher overnight.
Enter the exact day rate, night rate and standing charge from the Economy 7 tariff. Economy 7 often has a cheaper night rate but a higher day rate. Then enter the single-rate tariff you would otherwise use. The calculator compares total annual cost, including standing charges and any optional setup cost.
The break-even night share is important. It tells you the percentage of electricity that must move to the night rate before Economy 7 beats the single-rate tariff. If your current night share is 25% and break-even is 40%, the tariff is unlikely to help unless you can move a lot of use into the cheap window.
Formula and Method
night kWh = annual kWh x night use share
day kWh = annual kWh - night kWh
Economy 7 energy cost = day kWh x day rate + night kWh x night rate
Economy 7 annual cost = Economy 7 energy cost + Economy 7 standing charge x 365 + setup cost
single-rate annual cost = annual kWh x single-rate unit price + single-rate standing charge x 365
saving = single-rate annual cost - Economy 7 annual cost
break-even night share = rate difference needed to match the single-rate annual cost
All pence rates are converted to pounds before the final display. The calculator assumes rates stay fixed for the year. If your tariff changes part-way through the year, run one calculation for each rate period.
Night-Use Planning Table
| Use | Can it move to night rate? | Good candidate? | Check first |
|---|---|---|---|
| Storage heaters | Usually, if designed for off-peak charging. | Yes, often the main Economy 7 use. | Controls, insulation, heater age and comfort. |
| Immersion heater | Often, with timer and suitable cylinder. | Yes, if hot water is stored safely. | Timer settings, thermostat and legionella safety guidance. |
| EV charging | Often, with suitable charger and schedule. | Yes, if the car can charge during off-peak hours. | Charger settings, mileage need and cheaper specialist EV tariffs. |
| Dishwasher and washing machine | Sometimes, with delay start. | Small to moderate saving. | Fire safety, noise, leaks and appliance instructions. |
| Cooking and daytime work | Usually no. | No, unless routine changes. | High day rate may make these more expensive. |
Risks and Checks
- Confirm the clock: Meter time, GMT/BST changes and supplier settings can affect cheap hours.
- Do not run unsafe loads: Follow appliance safety advice before leaving machines unattended overnight.
- Check heating comfort: Cheap overnight heat is not useful if the home is cold in the evening.
- Compare standing charges: A lower unit saving can be reduced by a higher daily charge.
- Review after a month: Smart meter data can show whether the expected night share is real.
Worked Example
A home uses 4,200 kWh per year. It can move 42% of use to the night rate through storage heating and hot water. The Economy 7 day rate is 31p, night rate is 12p and standing charge is 57p per day. The comparison single-rate tariff is 24.67p per kWh with a 57.21p standing charge. The calculator compares both annual totals and shows whether the night-rate saving beats the higher day rate.
If the night share falls to 20%, the same day rate becomes much more expensive. This is why Economy 7 should be checked with real use data, not just the attractive night price.
Reading Your Meter Before Switching
For a fair comparison, record day and night readings at the same time of day for at least one normal week. A month is better where heating or hot water is involved. If the cheap period starts late at night, check whether appliances, storage heaters and immersion timers really run inside that period. A smart meter display or online account may show half-hourly use, but a manual meter can still work if it has separate day and night registers.
Seasonal use matters. A household with storage heaters may have a strong night share in winter and a weaker one in summer. If your supplier quotes annual figures, compare the full year rather than one mild week. If you are renting, check whether any meter or heater setting is locked, shared or controlled by the property setup before relying on the saving.
FAQ
Is Economy 7 always cheaper?
No. It depends on how much electricity you use at night and how high the day rate is compared with a single-rate tariff.
Are Economy 7 hours the same everywhere?
No. Cheap hours depend on supplier, meter, region and time settings. Check your bill or supplier details.
Should I include gas use?
No. This calculator compares electricity tariffs only. Gas heating changes your electricity night share but is not part of the electricity bill calculation.
What night share should I test?
Use real meter data where possible. If you are guessing, test a low, middle and high night share to see how sensitive the result is.
Can timers make Economy 7 cheaper?
They can help move hot water, storage heating, EV charging or appliances into the cheap period, but only if the tariff hours and appliance use match safely.
Sources
- Ofgem (2026) ‘Energy price cap unit rates and standing charges‘. Office of Gas and Electricity Markets.
- Energy Saving Trust (2026) ‘Heating and hot water‘. Energy Saving Trust.
- Citizens Advice (2026) ‘Check if an Economy 7 tariff is right for you‘. Citizens Advice.