Methodology

The calculation

The detailed examples below use US dollars and US sources. The UK calculation guide explains pounds, pence and Ofgem reference prices; the Australian calculation guide explains Australian dollars, bill rates and local tariff limits.

watts ÷ 1000 × hours per day × duty cycle = kWh per day
kWh per day × rate in cents ÷ 100 = dollars per day

Duty cycle is expressed as a fraction in the calculation: 50% is 0.5. Hourly cost uses the entered power and duty factor. Daily cost also uses the entered hours. This is a simplified steady-use model, not a simulation of an appliance or a building.

In watts-and-hours mode, monthly equivalents multiply daily energy by 30.44. Annual cost uses your chosen use days (365 by default). These constants are separately rounded, so twelve monthly equivalents do not exactly equal a 365-day annual total. Annual-energy mode instead preserves the entered annual kWh and divides its calculated cost by 12 for a monthly average.

Seasonal equipment is not assumed to operate year-round in your home. A 365-day annual equivalent is only a comparison at unchanged use. Choose the days you expect to use it, or multiply daily cost by the length of your season. This does not automatically account for temperature or changing runtime during the season.

Published electricity-price data

We use EIA residential average retail prices, in cents per kWh, covering the 50 states and Washington, DC. State data correspond to Electric Power Monthly, Table 5.6.A; the US series appears in Table 5.3. The stored observations currently cover August 2026. EIA may revise preliminary values.

A residential average describes a group of customers, not a quoted tariff available to every household. The displayed month is the period covered by the data. It can lag the current date because statistics take time to collect and publish. We are an independent website and are not endorsed by the EIA.

Estimated appliance inputs

Watts, default hours and duty cycles are illustrative class-level presets. They are not published EIA measurements and should not be treated as verified specifications for a particular model. A displayed range is a guide for choosing an input, not a guarantee that all models fall within it. We have not independently measured the appliances in this database.

Use model-specific electrical input specifications, a compatible energy monitor, an EnergyGuide label or measured utility data when available. A nameplate can list maximum power rather than average consumption. Motor horsepower and cooling output in BTU/hour are not the same as electrical input watts. Volts × amps gives apparent power; power factor can make the real watts different.

Duty cycle and measured consumption

A thermostat or compressor may switch an appliance between running and idle states. The duty factor approximates the share of selected hours at the stated draw. Real devices can also have standby consumption, defrost cycles, multiple heating stages or continuously variable power, which a single factor does not fully describe.

If the watts you enter are an average measured over the whole period, use 100% duty. If you already know energy consumption in kWh, multiply it directly by the electricity price. Applying another duty factor to either would reduce the result twice.

Using an EnergyGuide label

The FTC’s EnergyGuide explanation describes which appliances carry labels and why their printed annual cost is only an estimate. Test usage and national energy prices may differ from your circumstances.

For a label with annual kWh, choose “Annual energy (kWh/year)”. Annual kWh × your price per kWh estimates annual cost at your price under the label’s test assumptions. Monthly cost is annual cost divided by 12; the daily equivalent divides by 365. The tool does not claim every appliance has an EnergyGuide label or that a label is a measurement of your household.

Choose “Metered energy over a period” for kWh recorded over a stated number of elapsed days. Cost for that period is recorded kWh × your price. The 30.44-day and 365-day projections divide recorded kWh by elapsed days and multiply by the respective period. They assume the same daily average, so a short or seasonal reading may not represent a future month or year. For a cumulative meter, enter the end reading minus the start reading.

Choose “Energy per use or laundry load” for kWh per completed use and uses per active week. Cost per use is kWh per use × your price. Annual cost multiplies that by uses per active week and selected active weeks per year (52 by default, representing 364 days). Its monthly average is the annual cost divided by 12, including inactive weeks. A washer measurement may exclude external water heating; do not assume all energy, water or sewer charges are included.

Comparing heat pumps with resistance heating

The heating comparison holds delivered heat constant. Its resistance baseline assumes one kWh of electricity becomes one kWh of heat at the heater. If Q is heat required in kWh, C is the assumed heat-pump COP and b is the heat-output share from separate resistance backup, electricity use is Q × ((1 − b) / C + b). Cost is that electricity use times the entered price. No additional hours, duty cycle or annual multiplier is applied.

COP must represent the conditions and equipment boundary being compared, including applicable fans and defrost. If it already includes resistance backup, leave the separate backup share at zero. HSPF and HSPF2 are seasonal ratings in Btu per watt-hour, not dimensionless COP values; see ENERGY STAR’s definitions. Different rooms, distribution losses, temperature, capacity, installation and maintenance can change a real-world comparison.

Known limitations

The multiple-appliance planner adds separate loads: each row uses quantity × watts per item × daily hours ÷ 1,000. Its selected-period result repeats that full daily schedule for the exact entered number of days, using unrounded daily energy. Enter average power for the selected hours, or actual hours at a steady operating draw; no additional duty factor is applied. A group measurement already includes its devices, so use quantity 1 for that group and avoid adding the same energy again.

• Tariffs: a single rate does not model time-of-use periods, tiers, demand charges, credits or minimum bills. Use the applicable usage-based energy and delivery prices when estimating an added appliance load.
• Fixed charges: adding an appliance usually does not add another monthly service fee. Our model does not reconstruct the fixed and variable components of a state average or your full bill.
• Usage: size, settings, weather, maintenance and operating mode can change draw or runtime. State context is general background, not a home-specific forecast.
• Scope: results cover electricity at the entered rate. Water, sewer, other fuels, purchase, installation and maintenance costs are not included.
• Sources: external references explain rate data or a calculation method; they do not certify our preset wattages or every displayed estimate.

Corrections

Send a suspected error and its source or model information to contact@costtorunit.com. Please identify the page and input values so the calculation can be reproduced.

Currently 40 appliance presets and 51 locations (50 states plus DC). Rate period: August 2026. The rate period does not imply that appliance specifications were tested or reviewed that month.