Units and time periods
Energy in kWh equals power in kW multiplied by hours of operation. A cost estimate then multiplies energy by the selected unit price. Watts are divided by 1,000 before using that formula. Monthly and annual figures follow the time convention stated beside the tool; an average month is not necessarily the number of days on your bill.
Comparisons and simplified models
Comparisons keep the same price and observation period unless separate values are explicitly requested. Percentage savings use the original option as the denominator; a zero baseline cannot yield a meaningful percentage. Solar and heat-pump tools expose yield or efficiency assumptions. Simple payback divides the relevant investment by positive annual savings and excludes financing and discounting unless explicitly stated.
Review and reproduction
Formula tests cover normal inputs, conversions and important boundary cases. Display rounding is for readability and should not be mistaken for extra precision in the source data. Review dates identify content maintenance, not a guarantee that market prices remain current. To reproduce a calculation, keep its page, country, inputs, units and date, and consult the linked primary sources.
Data sources
- Ofgem · July–September 2026
- Ofgem: Understanding electricity and gas bills
- Ofgem: Price cap and standing charges explained
- Utility Regulator: Consumer information for Northern Ireland
Last reviewed: 2026-09-08