Calculation methodology

Active energy

For a scheduled appliance, annual active energy is:

Duty cycle represents the share of a scheduled operating period in which the appliance draws the entered power. A refrigerator preset, for example, uses a duty cycle because its compressor cycles. For an always-on device, the schedule is 24 hours a day, 365 days a year.

Seasonal schedule energy

Active days and standby days are independent values from 0 through 365. The model never infers standby days from the active season. Only visible seasonal fields are calculation inputs, and zero active days is a valid zero-active-energy case.

Per-use and per-cycle energy

For a measured complete-use value, annual active kWh equals measured kWh/use × uses/week × 365 ÷ 7 × quantity. Measured kWh per use bypasses watts, minutes and duty cycle. Cost per use means active electricity for one use; separately entered annual standby is not allocated across uses.

Two-scenario comparisons

Each side is first evaluated by the production schedule or per-use engine above. The Comparison Lab then applies one common rate and currency; it does not recalculate appliance energy through a second formula.

“As entered” preserves each independent annual schedule, basis, and quantity. “Matched uses” applies one visible shared uses/week value to both valid per-use results, then adds each side's separately entered annual standby. When Scenario B is zero, no finite percentage is reported. Equal use counts do not establish equal service, capacity, cooking performance, food quantity, quality, or outcome.

Standby energy

Eligible standby time cannot overlap scheduled active time. If active use averages 20 hours a day, standby is capped at 4 hours—even if a larger number is entered. Selecting “unplugged” makes standby energy zero.

Whole-home inventory aggregation

Every inventory item is evaluated by the same schedule, seasonal-schedule, or per-use production function described above. The inventory supplies one common rate and currency to every item; imported item-level rates, currencies, and calculated totals are ignored.

Room, category, and provenance subtotals are sums of the same item results and must reproduce the overall total. Largest contributors are sorted by annual kWh with original order retained for ties. Measured-input percentage is measured-provenance modeled kWh divided by all modeled kWh; no confidence score is inferred.

Bill-reference check

Coverage is unavailable when annualized bill kWh is zero. The check compares electricity consumption only and does not reproduce the final bill amount or diagnose a difference.

Costs and time periods

The interface displays money to two decimal places for readability, but the calculation retains unrounded values. A year is modeled as 365 days; weekly schedules use 365 ÷ 7.

Measured energy

A kWh meter reading is converted to an average power for the measured period. The calculator then applies the usage schedule. For cycling appliances, measure long enough to include representative on/off cycles. Do not add a separate standby amount if the measurement already includes standby.

Smart-plug payback

One smart plug is assumed per appliance. The entered price and continuous power are per smart plug, so total purchase cost and plug operating electricity both multiply by appliance quantity. No finite payback is reported when net savings are zero or negative. Five-year net benefit means five years of net annual electricity savings minus the complete initial purchase cost for all plugs.

Verified three-device example

For three appliances that each draw 10 W in standby, disconnecting them for 16 hours/day on five days/week at $0.30/kWh avoids $37.542857/year. Three smart plugs drawing 0.8 W continuously cost $6.3072/year to operate. Net annual savings are $31.235657/year. At $15 per plug, total purchase cost is $45, payback is 17.29 months, and five-year net benefit is $111.18.

Illustrative sensitivity bands

Results are estimates, not meter-grade measurements. The interface applies arithmetic sensitivity multipliers of ±5% for measured active input, −20% to +25% for label input, and −35% to +40% for illustrative presets. These site-defined bands show how the displayed total moves under a fixed multiplier; they are not meter specifications, guarantees, probability ranges, or statistical confidence intervals. A measured active input may still be combined with an unmeasured standby input.

Last reviewed: August 14, 2026