Calculation Methodology

All figures come from one fixed formula.

The formula

Energy (kWh) = watts ÷ 1,000 × hours
Cost = energy × price per kWh

Periods

Week = 7 days. Month = 30 days. Year = 365 days.

Appliances that cycle

Refrigerators, air conditioners and dehumidifiers do not run at full power all the time. For these we include the typical share of time at full power. You can change it in the calculator.

Wattage

Wattages are typical label values, not lab measurements. For exact use, measure with a plug-in energy monitor.

Rounding

Money is rounded only for display, after all steps are calculated.

Testing

The calculation engine is covered by automated tests with known results (for example 1,500 W × 8 hours at $0.18 = $2.16) and edge cases such as zero watts and large values.