Editorial standards: how we verify every number
People use these estimates to decide whether to run a heater for another hour or replace a fridge, so every figure goes through the same three-step verification before it is published. This applies to the homepage calculator, all twelve appliance calculators and every guide in the library. Written and reviewed by Y.W. Fung, founder and editor.
Step 1
Publish the formula, never a black box
Every estimate on this site uses one visible equation: kWh = (watts x hours) / 1000, multiplied by your rate per kWh, with any fixed daily standing charge added as a separate line. No hidden efficiency multipliers, no seasonal fudge factors, no rounding that flatters the result. Where duty cycle genuinely matters — refrigerators, heat pumps, thermostatically controlled heaters — we state the effective daily kWh and explain why it is lower than continuous draw. Because the arithmetic is printed on the page, you can reproduce any number we publish with a pocket calculator, and you can spot immediately when one of our assumptions does not match your household.
Step 2
Cross-check every input against official sources
Wattages start from manufacturer nameplate ratings and are checked against Energy Star product specifications and US Department of Energy appliance energy-use tables. Where a product family spans a wide range, we publish the range and default to a mid-market figure rather than a best case. Electricity rates are cross-checked the same way: the EIA average residential price for the US, the Ofgem price cap for the UK including its daily standing charge, CLP Power and HK Electric tariff sheets for Hong Kong, Taipower's residential blocks for Taiwan, and METI-published supplier tariffs for Japan. When two sources disagree, we use the regulator's figure and note the discrepancy in the guide.
Step 3
Test against real bills and real users
Before a calculator ships, its presets are tested with plug-in power monitors on real appliances and compared with readers' actual utility bills across the five markets we cover. Testers report a scenario, their tariff and their measured consumption; when our estimate is more than about 10% off for a steady-draw appliance, the default is corrected before publication. Readers keep reporting mismatches after launch, and those reports are treated the same way as a regulator change.
Review cycle and corrections
Rate defaults are reviewed at least twice a year and immediately after a published regulator change such as an Ofgem cap adjustment. Guides carry a visible last-updated date, and when a figure changes materially the article body changes with it rather than only the date. To report an error, email hello@proenergysaver.app with your supplier, tariff name and the figure you measured; we reply within 48 hours and corrections are made directly in the affected page.
Independence and limitations
ProEnergySaver is independent and is not sponsored by any utility, retailer or appliance manufacturer. The site participates in the Amazon Services LLC Associates Program and may carry contextual advertising; neither influences our recommendations. Our figures are educational estimates, not billing statements: they do not model tiered block tariffs, demand charges, taxes and levies, power factor, or extreme ambient temperature effects on compressor efficiency. All calculations run 100% in your browser and nothing you enter is uploaded.
Frequently asked questions
How accurate are ProEnergySaver estimates?
Within roughly 5-10% of a metered reading for steady-draw appliances when you enter your own rate and realistic hours. Thermostatic appliances such as fridges and heat pumps vary more because their duty cycle depends on ambient temperature.
Where do the default electricity rates come from?
US rates follow the EIA average residential price, UK rates and standing charges follow the Ofgem price cap, and Hong Kong, Taiwan and Japan use the published residential tariffs of CLP Power, Taipower and METI-listed suppliers.
Do you accept payment to feature an appliance or supplier?
No. ProEnergySaver is independent, takes no utility or manufacturer sponsorship, and no advertiser reviews content before publication. Amazon affiliate links never change which appliance is recommended.
Last updated: September 2026. See also our about page, privacy policy and terms of service.