Economy 7 and storage heater calculator
Compare annual costs, find your break-even night share and include new night-time loads.
After you calculate
Your tariff comparison
Enter your usage and tariff prices to compare yearly costs.
Economy 7 annual bill
Shown after calculationSingle-rate annual bill
Shown after calculationDay and night use
Break-even night share
Full calculation
Includes the standing charges and additional night loads you enter.
Understand your estimate
How it works
Enter annual electricity use, the night-register share and your supplier's day/night prices. Compare with a published single-rate benchmark or your own quote; both tariffs include standing charges.
Add new heater, EV or dehumidifier night loads only if they are absent from the annual total. The final total kWh is the same for both tariffs.
Use meter or bill records for the night share when you have them. It is the share of energy charged at night, rather than the share of the day spent using electricity. Check that the annual total and night share cover the same period.
- Start with your bill
Enter total annual kWh and the share charged at night.
- Add the prices
Use actual day, night and single-rate prices and standing charges.
- Compare both bills
Read annual costs and the night share needed for the costs to match.
A few good questions
Before youget started.
Understand this calculator, the figures to enter and the limits of your estimate.
Sources
- Energy price cap unit rates and standing chargesChecked on 9 October 2026
- Last checked
- 13 October 2026
- Rates as of
- 1 October 2026
EnergySums
Economy 7 and storage heater calculator
United Kingdom · How it works
- Guide updated
- 13 October 2026
- Rates as of
- 1 October 2026
| Item | Value |
|---|---|
| Guide updated | 13 October 2026 |
| Rates as of | 1 October 2026 |
How it works
Enter annual electricity use, the night-register share and your supplier's day/night prices. Compare with a published single-rate benchmark or your own quote; both tariffs include standing charges.
Add new heater, EV or dehumidifier night loads only if they are absent from the annual total. The final total kWh is the same for both tariffs.
Use meter or bill records for the night share when you have them. It is the share of energy charged at night, rather than the share of the day spent using electricity. Check that the annual total and night share cover the same period.
- Start with your bill
Enter total annual kWh and the share charged at night.
- Add the prices
Use actual day, night and single-rate prices and standing charges.
- Compare both bills
Read annual costs and the night share needed for the costs to match.
Formula
Unit prices are in p/kWh and standing charges in p/day. Annual use includes any added night loads.
Split the final annual kWh into day and night energy. Price each part separately, then add a year's standing charges. For single rate, price all final kWh at the same unit price and add that tariff's standing charges. The difference compares these two totals.
Read the final night share after any extra loads are added. That can differ from the base bill's night share. Compare the break-even point with this final share. If you change a price or standing charge, check the threshold again. A small difference between the bills can change when your routine or the tariff changes.
- Base night use
- Base annual kWh × (night percentage ÷ 100)= base night kWh
- Day use
- Base annual kWh − base night kWh= day kWh
- Total night use
- Base night kWh + added night kWh= night kWh
- Economy 7 / year
- (Day kWh × day rate (p/kWh) + night kWh × night rate (p/kWh) + 365 days × E7 daily charge (p/day)) ÷ 100 p/GBP= annual cost
- Single rate / year
- (Total kWh × single rate (p/kWh) + 365 days × single daily charge (p/day)) ÷ 100 p/GBP= annual cost
- Monthly average
- Annual cost/year ÷ 12 months/year= monthly cost
- Extra cost before shifting use
- Total kWh × (day rate − single rate) + 365 days × (E7 daily charge − single daily charge)= extra annual cost in penceUse p/kWh for unit prices and p/day for daily charges. Assume all use is daytime for this step.
- Saving from shifting all use
- Total kWh × (day rate − night rate)= annual saving in penceUse the same total annual kWh. This is the saving if all that use moved from day to night.
- Break-even night share
- (Extra annual cost ÷ saving from shifting all use) × 100= night percentageBoth amounts must use the same currency unit. Only divide when the saving is nonzero; interpret thresholds outside 0–100% using the comparison result.
| Calculation | Formula with saved values | Result |
|---|---|---|
| Base night use | Base annual kWh × (night percentage ÷ 100) | base night kWh |
| Day use | Base annual kWh − base night kWh | day kWh |
| Total night use | Base night kWh + added night kWh | night kWh |
| Economy 7 / year | (Day kWh × day rate (p/kWh) + night kWh × night rate (p/kWh) + 365 days × E7 daily charge (p/day)) ÷ 100 p/GBP | annual cost |
| Single rate / year | (Total kWh × single rate (p/kWh) + 365 days × single daily charge (p/day)) ÷ 100 p/GBP | annual cost |
| Monthly average | Annual cost/year ÷ 12 months/year | monthly cost |
| Extra cost before shifting use | Total kWh × (day rate − single rate) + 365 days × (E7 daily charge − single daily charge)Use p/kWh for unit prices and p/day for daily charges. Assume all use is daytime for this step. | extra annual cost in pence |
| Saving from shifting all use | Total kWh × (day rate − night rate)Use the same total annual kWh. This is the saving if all that use moved from day to night. | annual saving in pence |
| Break-even night share | (Extra annual cost ÷ saving from shifting all use) × 100Both amounts must use the same currency unit. Only divide when the saving is nonzero; interpret thresholds outside 0–100% using the comparison result. | night percentage |
- Break-even holds the final total kWh constant.
- Equal day/night prices or a threshold outside 0–100% may mean Economy 7 is always cheaper, never cheaper or the same cost.
Worked example
Illustrative day/night quotes, compared with the Great Britain average Direct Debit single rate for 1 October 2026 to 31 December 2026.
- Annual base use
- 3400 kWh
- Night share
- 40%
- Day / night quote
- 32p / 12p per kWh
- Single rate
- 26.32 p/kWh
| Item | Value |
|---|---|
| Annual base use | 3400 kWh |
| Night share | 40% |
| Day / night quote | 32p / 12p per kWh |
| Single rate | 26.32 p/kWh |
- Night use
- 3,400 kWh × (40 ÷ 100)= 1360 kWh
- Day use
- 3,400 kWh − 1,360 kWh= 2040 kWh
- Economy 7 / year
- (2,040 kWh × 32 p/kWh + 1,360 kWh × 12 p/kWh + 365 days × 54.62 p/day) ÷ 100 p/GBP= £1,015.36
- Single rate / year
- (3,400 kWh × 26.32 p/kWh + 365 days × 54.83 p/day) ÷ 100 p/GBP= £1,095.01
- Annual saving
- £1,095.01 − £1,015.36= £79.65
- Heater / night
- 3.4 kW × 7 hours= 23.8 kWh
- Heater / year
- 23.8 kWh/night × 120 nights= 2856 kWh
| Calculation | Formula with saved values | Result |
|---|---|---|
| Night use | 3,400 kWh × (40 ÷ 100) | 1360 kWh |
| Day use | 3,400 kWh − 1,360 kWh | 2040 kWh |
| Economy 7 / year | (2,040 kWh × 32 p/kWh + 1,360 kWh × 12 p/kWh + 365 days × 54.62 p/day) ÷ 100 p/GBP | £1,015.36 |
| Single rate / year | (3,400 kWh × 26.32 p/kWh + 365 days × 54.83 p/day) ÷ 100 p/GBP | £1,095.01 |
| Annual saving | £1,095.01 − £1,015.36 | £79.65 |
| Heater / night | 3.4 kW × 7 hours | 23.8 kWh |
| Heater / year | 23.8 kWh/night × 120 nights | 2856 kWh |
- Day/night prices are illustrative quotes, not published cap defaults. Standing charges are 54.62p/day for Economy 7 and 54.83p/day for single rate.
- The heater example is a separate additional load; it is not included in the tariff totals above. Add it only if absent from base use. Actual charging controls may reduce consumption.
- Totals use unrounded values; money is rounded for display.
Assumptions and limits
The break-even share helps you test a tariff, rather than telling you to run more equipment. Compare it with use you can actually move into the night window. Keep the total kWh steady when testing a different split.
- Both tariffs supply the same final kWh. Extra loads run fully in the night window; avoid counting existing bill usage twice.
- Use heater input kW rather than heat output, and EV electricity measured at the meter, including charging losses. Dehumidifier watts stay constant during entered hours.
- The year is 365 days; monthly figures are annual averages. Rates stay fixed, without discounts, fees, exit charges or later changes.
- Break-even compares prices at the same total use. Adding avoidable consumption can increase spending even at a cheaper night price.
Country rules
Published single-rate prices use the stored Ofgem table for your region and payment method in Great Britain. Published electricity defaults include 0% VAT for this period. Both tariff totals include the daily standing charge you select or enter. Check the source period and your supplier quote before comparing them. A cheaper rate does not place a limit on your total bill.
- Ofgem's multi-register cap is a blended figure, not a universal day/night price pair. Enter actual supplier quotes.
- Published multi-register standing charges apply to the selected region and payment method. Northern Ireland is outside the cap.
- Confirm your supplier's seven-hour window and clock-change rules before scheduling night loads.
When to ask a professional
Have your meter readings and both tariff quotes ready. Ask the adviser to check that the prices, standing charges and night window match your supply.
- Energy adviser: advice on tariff suitability.
- Installer or electrician: advice on heater controls, wiring or replacement.
- Follow the manufacturer's instructions. This tool does not assess circuit safety, heater sizing or room comfort, or advise changing wiring or metering controls.
Questions and answers
| Question | Answer |
|---|---|
| Is Economy 7 heating expensive? | It depends on the heater's electricity consumption, night share and both tariff prices. Compare the entire annual bill, including day use and standing charges, rather than judging it from the night rate alone. |
| Are storage heaters expensive to run? | Multiply charging input kW by actual charging hours and your unit price. A full-input estimate can exceed real consumption when charging is controlled. Add daytime boosts separately. |
| Is it cheaper to leave storage heaters on all the time? | A cost estimate cannot prescribe a control setting. Follow the manual and confirm which circuit charges at night. Modern controls may regulate charging; do not assume that switched on means full-power consumption all day. |
| Does a storage heater use a lot of electricity? | At full input, a 3.4 kW heater charging for seven hours uses 23.8 kWh. These are example inputs, not a typical daily requirement. Actual use varies with its controls and heat demand. |
| What time does Economy 7 turn on? | The seven cheaper hours depend on your supplier, meter and region. Check the tariff documentation and meter, including clock-change arrangements. There is no single night window built into this calculator. |
Sources
| Source | Checked | Reference URL |
|---|---|---|
| Energy price cap unit rates and standing charges | 9 October 2026 | https://www.ofgem.gov.uk/information-consumers/energy-advice-households/get-energy-price-cap-standing-charges-and-unit-rates-region |