One consistent year
Every estimate uses a 365-day year. A week is annualized by 365 ÷ 7. An average month is one twelfth of the yearly result, not a fixed 30-day billing period. Values are calculated at full precision and rounded for display.
Energy formulas
Known kWh/day: kWh × 365
Known kWh/week: kWh × 365/7
Known kWh/month: kWh × 12
Known kWh/year: kWh
Measured period: measured kWh ÷ measured days × 365
Per cycle: kWh/cycle × cycles/week × 365/7
Per 100 cycles: kWh/100 cycles ÷ 100 × cycles/week × 365/7
From energy to cost
The same applied rate and currency are used in all tools. No exchange-rate conversion takes place. Zero is an accepted input; an empty field is not treated as zero. Rates are non-negative, schedules cannot exceed 24 hours/day or 7 days/week, and appliance quantities are positive whole numbers.
Comparing purchase and electricity costs
For two new appliances, the modeled cost over a chosen period is the purchase price plus annual electricity cost multiplied by years. For keeping an existing appliance versus replacement, the existing appliance has zero new purchase cost. Its historic purchase price is excluded as a sunk cost.
The replacement outlay is the entered purchase price, plus delivery and installation only when selected, minus sale or trade-in proceeds only when selected. Unselected costs are excluded and identified. Results are not a full cost-of-ownership analysis.
Payback is shown only when there is a positive additional investment and positive annual saving. A cheaper upfront option needs no premium recovered. Zero or negative savings do not recover a positive premium through electricity savings. A payback beyond the selected period is identified. No discounting, inflation, degradation or future tariff changes are modeled.
A budget of selected appliances
Each row’s yearly energy is multiplied by quantity. Row contributions refer only to the selected appliances. An optional fixed monthly charge is shown separately. A baseline is a snapshot of appliance inputs and fixed charges, evaluated at the same current rate as the working scenario.
What a result cannot tell you
It cannot certify electrical safety, recommend wiring or equipment sizing, predict a whole-home bill, or guarantee savings. Label figures use test conditions. Measured periods may not represent another season. Power ratings may overstate average draw. The estimate is only as representative as the inputs.
Sources and maintenance
Core unit relationships and original worked examples are implemented directly in the calculation engine. Context is checked against Australian Government: energy rating, US Federal Trade Commission: EnergyGuide labels, and European Commission: washing machines. Formula and validation changes should pass automated calculation tests before release.
Calculation version: 1.0 · Reviewed 20 October 2026.