Small Home Energy
How we calculate appliance electricity costs
How the calculators and research-based guides turn inputs into a decision you can examine.
Running cost
Daily kWh = average watts ÷ 1,000 × hours per day
Monthly kWh = daily kWh × days per month
Monthly cost = monthly kWh × $/kWh
Annual cost = monthly cost × months used
The rate is an input, not a live tariff lookup. The default $0.18/kWh is a round illustrative value. Use the applicable variable rate on your own bill. Fixed fees, demand charges and time-dependent prices are not modeled automatically.
The annual result repeats the specified month. Entering 31 days and 12 months represents 372 usage days, not a calendar year. For 365-day planning, enter 30.4167 days per month with 12 months. For seasonal use, choose the months you actually expect to use the device.
Variable power and cycling
For a measured total, divide kWh by the measurement hours and multiply by 1,000 to obtain average watts. Use that average with a matching schedule. Do not apply a cycling discount a second time. Nameplate watts create a constant-draw scenario and may differ substantially from typical operation.
Measured energy and annual-energy inputs
Measured-energy mode divides observed kWh by the complete observation hours, including idle periods, and projects that average across 24 hours daily. Use a representative continuous period. A single operating cycle is not a continuous daily routine. Annual-energy comparison multiplies each annual kWh figure by your electricity rate, without applying hours, days or months again. Compare annual figures on compatible assumptions.
Total ownership comparison
Total cost = purchase price + annual electricity cost × years
Simple break-even = purchase premium ÷ annual energy saving
In watts mode, the two options share the same hours, days, months and rate. In annual-energy mode, they share the electricity rate and ownership period. Compare appliances capable of doing an equivalent job. Electricity prices and use remain constant in this model. Installation, maintenance, repairs, financing, resale, inflation and product lifespan are excluded.
When the higher purchase cost has no lower running cost, the tool reports no break-even. When the purchase prices are equal, running costs determine the difference. The calculation does not predict which appliance will last longer.
Research and authorship
Articles link to the public sources used. Government and certification sources support technical background; manufacturer material is identified when it is used. Numerical examples are our own arithmetic scenarios. We do not attribute hypothetical power values or prices to real products.
AI assisted with preparing this edition’s writing and site. That does not constitute professional engineering review or hands-on testing. No professional credentials, customer experiences or product measurements are invented.
Updates and corrections
Content-updated dates identify editorial changes; publication dates are recorded when the public edition is prepared. They do not promise automatic research updates. Tariffs, products and official guidance should be rechecked before a purchase. Contact information and correction guidance.