Our Methodology

Dividing watts by 1,000 converts the appliance's power to kilowatts. Kilowatts multiplied by hours gives kilowatt-hours (kWh). Multiplying kWh by the electricity rate gives the estimated energy cost. Hourly cost uses one hour; daily cost uses the daily runtime entered.

A 30-day estimate is the daily result multiplied by 30. Where a calculator shows a yearly estimate from daily use, it multiplies the daily result by 365. It does not multiply the 30-day estimate by 12.

Annual-kWh mode uses the annual energy figure entered from a model-specific EnergyGuide label, manufacturer specification, or other applicable product data. Annual cost is annual kWh multiplied by the rate. For a 30-day estimate, the calculator divides annual kWh by 365 and multiplies the daily average by 30.

Per-cycle mode multiplies kWh per cycle by the entered cycles per week, divides by 7 for a daily average, and uses that average for 30-day and 365-day estimates. The displayed per-cycle cost is kWh per cycle multiplied by the rate. These modes can be more suitable than nameplate watts for appliances whose power changes during a cycle.

Calculators begin with the configured EIA U.S. or selected-state average residential electricity rate. If you enter the electricity rate from your bill, that value replaces the average in the calculation. For the closest simple energy-rate estimate, use total electricity charges divided by billed kWh when that matches how you want to compare usage.

EIA state averages describe average residential prices for a state and period; they are not an individual utility tariff. Fixed charges, taxes, tariff tiers, demand charges, credits, time-of-use prices, and other bill adjustments may not be represented.

Air-conditioner runtime is treated as full-load-equivalent hours: the energy of running at the entered wattage for that many hours. A cycling or variable-speed system may run for more clock hours while averaging less than nameplate power.

Refrigerators, dehumidifiers, heat pumps, and other cycling or variable-speed appliances may not continuously use their nameplate wattage. Measured energy, annual-kWh data, or per-cycle data is preferable when it is available for the exact model and use pattern.

When amount, kWh, and billing days are available for both bills, the comparison calculates kWh per day and effective all-in cost per kWh for each period. The billing-period effect holds the previous daily use and effective cost constant. The daily-usage effect holds the previous effective cost constant.

The remaining rate-and-charge effect is current amount minus current kWh multiplied by the previous effective all-in cost. It is not described as a pure rate increase because tariffs, fixed charges, taxes, credits, or other bill components may contribute. The three raw effects reconcile to the bill change; displayed effects are reconciled again at displayed precision.

CEER mode applies the labeled room-air-conditioner relationship only when the capacity and rating are compatible. It is not automatically valid for central AC, mini-splits, or equipment using noncomparable ratings. Watts mode uses full-load-equivalent runtime, and annual-kWh mode uses the entered yearly figure.

Measured mode divides measured kWh by the known number of hours or days to obtain an average daily value, then projects that same average across 30 days, the entered cooling season, and 365 days. Lower and higher scenarios adjust entered use by the disclosed percentage and are not forecasts.

When a current appliance still works, net upfront cost is purchase price plus installation and other cost minus rebate. When replacement is already necessary, the comparison uses only the efficient option incremental premium over the standard option.

Verdicts first require comparable capacity and service, then consider input basis, positive savings, the configured close threshold, and whether simple payback fits within the intended ownership period. The comparison excludes financing, maintenance, reliability, disposal, comfort, safety, and non-energy benefits and is not financial or professional advice.

Comparison tools calculate each entered scenario independently, then compare the displayed cost values. The lower-cost direction, equality result, and displayed difference use the same rounding precision shown to the user. The underlying calculations can retain more precision than the formatted values on screen.

A cost comparison is not a claim that two appliances provide the same service. Heating comfort, moisture removal, cooling, capacity, controls, runtime, and operating conditions can differ even when the entered electricity costs are compared.

The Home Energy Cost tool adds the 30-day energy-cost estimates for the appliances currently listed. It is a listed-appliance subtotal, not a whole-home bill forecast. Each row can use watts and daily runtime, annual kWh, or per-cycle energy.

The Home Energy Breakdown tool converts each listed appliance to kWh for the selected billing-period days, adds those kWh and energy costs, and groups the same values by category. If actual bill kWh is entered, it calculates the following reconciliation values:

An entered total bill amount remains separate from the listed-appliance energy-cost subtotal. Their difference can include fixed fees, taxes, tariff effects, credits, unlisted loads, standby use, cycling, and estimation error.

Weather, insulation, thermostat settings, room size, air leakage, humidity, appliance condition, maintenance, standby loads, and actual usage all affect energy use. WattItCost estimates the scenario entered; it does not reproduce meter data or an individual utility bill.

A plug-in energy monitor can provide measured consumption for compatible appliances. Utility statements and the utility's tariff remain the authoritative sources for billing questions.