Estimate annual bill savings, net project cost and simple payback from reducing household electricity and gas use.
Calculate your potential home energy savings
Estimate uses illustrative Oct–Dec 2026 average Direct Debit rates: 26.32p/kWh electricity and 7.97p/kWh gas, plus standing charges of 54.83p/day and 29.68p/day. Standing charges are not reduced.
How to use this calculator
Enter the annual electricity and gas consumption shown on your bills, then add realistic percentage reductions for your planned measures. Include the installation cost, any annual maintenance cost and confirmed grant contribution. The calculator estimates savings at the stated energy rates and displays a simple payback period.
Calculation method
| Result | Method |
|---|---|
| Energy saved | Annual kWh × expected reduction percentage |
| Gross bill saving | Electricity saved × £0.2632 + gas saved × £0.0797 |
| Net annual saving | Gross bill saving − extra annual maintenance or running cost |
| Net project cost | Upfront cost − grant or contribution, not below £0 |
| Simple payback | Net project cost ÷ net annual saving |
Choosing realistic savings percentages
The reduction depends on the building, household behaviour and measure installed. Insulation and draught-proofing mainly affect heating demand, while appliance upgrades and solar generation can affect purchased electricity. Use a survey, installer estimate or monitored data where possible. The Energy Saving Trust explains common home energy-efficiency improvements and their practical role.
Standing charges and changing tariffs
This estimate keeps electricity and gas standing charges unchanged because they normally remain payable while a supply is active. Unit rates, standing charges and tariffs can change, so compare the estimate with your latest bill before making a decision.
Understanding simple payback
Simple payback shows how long estimated net savings would take to recover the net upfront cost. It does not model future price changes, inflation, finance interest, equipment degradation, replacement costs, property value or non-financial benefits such as improved comfort.
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Frequently asked questions
Does the calculator reduce standing charges?
No. It assumes standing charges continue unchanged and applies savings only to reduced unit consumption.
What reduction percentage should I enter?
Use a figure supported by an energy assessment, installer estimate or measured household data rather than a best-case claim.
Are grants included?
Yes. Enter a confirmed grant or contribution and it is deducted from the upfront cost, without allowing the net cost to fall below zero.
Does the payback include inflation or finance costs?
No. It is a simple payback estimate and does not include inflation, borrowing costs, tariff changes or investment returns.
Can renters use this calculator?
Yes, but renters should obtain the landlord’s permission before making building alterations and should separate measures they can take with them when moving.