Annual-kWh mode
The annual estimate is annual kWh × cents/kWh ÷ 100. Monthly and weekly averages divide that annual result by 12 and 52. The calculator does not redistribute energy by calendar month or season.
If a printed yearly estimate is supplied, the dollar difference is recalculated annual estimate - printed annual estimate. The percentage difference divides that amount by the printed estimate. A percentage is unavailable when the printed estimate is zero. The implied price is printed annual estimate × 100 ÷ annual kWh.
Watts and runtime mode
Energy per use is watts × hours per use ÷ 1,000. The selected use count is annualized with 365 days, 52 weeks, 12 months, or 1 year. Annual energy equals energy per use multiplied by annual uses. Cost uses the same cents-to-dollars conversion as annual-kWh mode.
The mode assumes the entered watts apply for the full entered runtime. It does not infer cycling, variable load, standby power, or seasonal changes.
Validation and precision
Required inputs must be positive finite numbers within documented practical bounds. The optional printed estimate may be zero. Inputs are never silently clamped.
Money calculations use scaled integers internally. Energy and average-period presentation may use fractional values. Currency is rounded to cents only when displayed, while energy display uses a limited number of decimal places.
Scope of every estimate
This calculation models energy costs for one appliance using your entered usage and price assumptions. Actual runtime, load, conditions, and price changes can affect costs. It does not separately calculate fixed charges, taxes, tiers, time-of-use pricing, demand charges, riders, billing periods, or future prices. A whole-bill effective price may already include fixed charges, taxes, or other items indirectly. It will not match an actual utility bill in many cases. This release uses only the cents-per-kWh value you enter. If a later reviewed release adds an EIA benchmark, it would be a dated state residential average revenue per kWh, not your utility rate.