How WattFigure calculates electricity cost

The calculation

Energy for one use day is calculated as watts ÷ 1,000 × hours × quantity × duty-cycle fraction. Monthly energy is that daily result multiplied by use days per month. The annual planning figure is the monthly result multiplied by 12. Cost is energy multiplied by the electricity rate in dollars per kilowatt-hour.

daily kWh   = watts / 1,000 × hours × quantity × duty cycle
monthly kWh = daily kWh × use days per month
annual kWh  = monthly kWh × 12
cost        = kWh × cents per kWh / 100

What duty cycle means

A thermostat or compressor often turns the high-power part of an appliance on and off. A 40% duty cycle means the rated power is treated as active for 40% of the entered time. It is an estimate, not a universal product specification. A plug-in energy meter or a label showing annual kWh can provide a stronger starting point.

Reference electric rates

The state selector uses preliminary residential average prices from the U.S. Energy Information Administration’s Electric Power Monthly, Table 5.6.A, for May 2026, released July 23, 2026. EIA calculates average price from reported revenue divided by sales. It is useful for a reference scenario but is not a specific tariff and may include effects that differ from your bill.

You can replace the reference with your own cents-per-kWh value. For a rough bill-derived rate, divide electricity-related variable charges by billed kWh. Fixed customer charges may not change when one appliance uses less electricity, so including them can overstate marginal savings.

Privacy and storage

The calculator runs in your browser. Appliance entries are stored only in sessionStorage so a refresh does not erase your worksheet. They are cleared when that browser session ends. WattFigure does not submit calculator entries to the server.

Limits

Real consumption can change with temperature, controls, standby power, voltage, equipment age, maintenance, load size, and user behavior. Monthly billing periods are not all 30 days, and seasonal use should not automatically be multiplied across a year. Results are for general information and planning, not a utility quote, engineering assessment, safety instruction, or savings guarantee.