Methodology & sources

Everything on this site comes from one formula and two datasets. Both are described in full here so you can check any number we publish.

The formula

Cost is then kWh × rate. Where:

• W — power in watts drawn while the appliance is actively working
• D — duty cycle: the fraction of "on" time the appliance actually draws W. A toaster is 1.0; a refrigerator is about 0.4; a hot tub heater is about 0.07 averaged over a year
• H — hours per day the appliance is switched on
• N — days per year it is used at all

Rate data

Residential electricity rates come from the US Energy Information Administration's Electric Power Monthly, Table 5.6.A — average retail price of electricity to residential customers by state. Current edition: EIA Electric Power Monthly, May 2026 data (released August 2026).

These are effective averages: total residential revenue divided by total residential kilowatt-hours sold. They therefore include generation, transmission, distribution and most fixed charges. They are the right figure for comparing states and the right default for estimating, but your own effective rate may differ because of fixed monthly charges, tiered pricing or time-of-use plans. To find yours, divide your bill total by the kilowatt-hours it lists.

Wattage and consumption data

Appliance figures are compiled from:

• US Department of Energy, Energy Saver — appliance energy use estimation guidance and the standard consumption formula
• ENERGY STAR product criteria and typical-use annual consumption figures
• Federal appliance efficiency standards, which set the consumption ceilings that define what a "typical" modern unit uses
• Manufacturer nameplate ratings across current mainstream models, from which we take a representative range rather than a single best or worst case

Duty cycles

This is the part most cost estimates omit, and the part most likely to be challenged, so here is how we set it. Where a published annual consumption figure exists — refrigerators, dryers, dehumidifiers and water heaters all have established ones — we solve for the duty cycle that reproduces it from the nameplate wattage and typical usage. Where no such figure exists, we use engineering values for the appliance class: thermostat-controlled resistance heating at 0.5–0.75 depending on insulation, compressor cooling at 0.6–0.7 during a cooling season, and continuously loaded devices at 1.0.

Duty cycle is a modelling assumption, not a measurement of your appliance. It is shown in the wattage chart for every entry so you can substitute your own.

Assumptions we apply site-wide

• Heating season: 120 days. Cooling season: 120 days. Pool season: 180 days.
• Laundry: 4 loads per week, 208 per year.
• EV driving: 12,000 miles a year at 0.30 kWh per mile, including charging losses.
• Typical household monthly consumption: 900 kWh, the EIA reference figure.
• Natural gas comparisons: $1.20 per therm through a 90% efficient furnace.
• Gasoline comparisons: $3.20 per gallon.

What these numbers are not

They are estimates for a representative US household, not a prediction of your bill. Real consumption depends on your specific model, your insulation, your climate, your habits and your utility's rate structure. Where we can, we show a range rather than a single figure, and every calculator lets you replace our assumptions with your own.

For a measured figure rather than an estimated one, a plug-in energy monitor costs about $25 and settles the question for any 120 V appliance in a week.

Updates

Rate data is reviewed when the EIA publishes a new Electric Power Monthly, which is roughly monthly. Appliance data is reviewed annually and when federal efficiency standards change. The update date at the top of each page reflects the last review of that page.