How we calculate
We combine published electricity prices with editable estimates of power and use. Here is how to check the calculation.
From watts to electricity cost
The examples below use US dollars. For local currency, tariffs and label guidance, use the UK calculation guide or Australian calculation guide.
A watt measures power. A kilowatt-hour (kWh) measures energy used over time. If your rate is in cents, divide it by 100 to get dollars per kWh.
kWh = (watts ÷ 1000) × hours of use × duty cycle
cost in dollars = kWh × rate in cents per kWh ÷ 100
A 1,500W heater drawing full power for eight hours uses 1.5 × 8 = 12 kWh. At an illustrative 20 cents/kWh, that costs $2.40. This is a worked example, not a measured household bill.
Choose power and runtime that describe your appliance
Check the model label or manual for input power in watts. A nameplate may show maximum input rather than normal draw. Multiplying volts by amps gives volt-amperes; it does not always equal real watts for motors and electronic equipment. A compatible energy monitor or model-specific energy data can give a better estimate.
For equipment that cycles on and off, the duty cycle is the share of the selected hours spent at the stated power. Enter 50% as 0.5 in the formula. Standby loads, variable-speed operation and different heating stages may need separate estimates.
If you already have average measured watts over the whole time period, use 100% duty cycle. Applying another duty factor would count the off-time twice. The same principle applies to measured kWh: multiply the energy by your price directly.
Monthly and seasonal estimates
In watts-and-hours mode, the monthly equivalent is daily use multiplied by 30.44 days. Annual cost uses your selected use days (365 by default). Twelve monthly equivalents differ slightly from a 365-day total because these constants are separately rounded. Direct-energy modes use the periods described below.
For heating, cooling or other seasonal equipment, a monthly equivalent describes a month at the selected daily use. It is not a forecast for every month of the year. On appliance calculators, change the annual-use days to estimate a shorter season. For example, $2.40 per use-day over 90 days is $216; over 365 days it is $876.
Where electricity prices come from
Our state benchmarks are residential average retail prices from the US Energy Information Administration (EIA), Electric Power Monthly, Table 5.6.A. The national series is in Table 5.3. The data currently shown cover August 2026, which is the observation period, not a claim about today’s tariff. Recent EIA data can be preliminary and revised.
A state average is a useful starting point. For the incremental cost of an appliance, use your applicable usage-based price per kWh, including usage-based delivery charges where relevant. Fixed monthly charges are not incurred again for each appliance. Time-of-use rates, tiers and demand charges require more detail than this single-rate model.
What the appliance presets mean
Preset watts, hours and duty cycles are illustrative estimates for appliance classes. They are not EIA measurements or measurements of a particular product. Replace them with your model’s input power and your usage when possible.
For a refrigerator or freezer, annual kWh on the EnergyGuide label can be more useful than a generic wattage. Multiply annual kWh by your local price to estimate annual electricity cost under the label’s test assumptions. The FTC explains how to read EnergyGuide labels and why the printed dollar estimate may differ from your cost. Choose “Annual energy (kWh/year)” in the calculator and enter the label energy directly. The calculator keeps that annual energy and divides its calculated annual cost by 12 for a monthly average.
Your calculator inputs
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