Workspace
The calculator's own fields, action and results arrive with the verified pack when you load it. Nothing is computed in this page.
Household energy · the always-on load
Standby (vampire) power annual cost
Annualise the trickle a device draws while nominally off — idle watts, hours and days, priced at your tariff — what never switching off actually costs.
Verified engine
What the engine returns
The engine returns the year’s idle energy and its cost. Read the energy figure against a real month of household consumption from the bill page — one silent box against the meter’s total — and then remember the box is rarely alone: the honest household figure is this calculation summed over everything that glows in the dark.
Inputs the result is built from
Standby (idle) power draw
Hours per day on standby
Days per year
Electricity tariff
How the result is derived
MethodThe idle draw is scaled to kilowatts and multiplied through hours per day and days per year to give annual idle energy, which the entered tariff prices; the declared reverse workflow solves for the continuous draw that produces a target annual cost.
StandardPhantom-load relation, annual cost = idle watts ÷ 1000 × hours per day × days per year × tariff
GuardA zero idle draw is refused — the pack ships that refusal as a declared test vector — because a device drawing nothing has no standby cost to compute, and a silent zero would bury the commonest cause: a milliwatt figure entered in the wrong unit.
How the annual cost moves with the standby draw
How single-digit watts become a yearly sum worth acting on
Standby — vampire or phantom load, in the older names — is the power electronics draw while doing nothing you asked for: holding a clock, listening for a remote or a network packet, keeping a transformer energised. Each individual draw is small, single digits of watts as a rule. What distinguishes it from every load the appliance page prices is not the size but the DUTY: a heater runs for hours, standby runs for all of them.
The arithmetic is a chain of small multiplications — watts scaled to kilowatts, times hours per day, times days per year, times the tariff — and the chain is why intuition fails here. Each factor is unremarkable; their product is not. The same structure explains why the daily cost of any one device rounds to nothing and why acting on that rounding is a mistake: the year is the honest window for a load that never stops, and the pack’s formulation is annual for exactly that reason.
The entered wattage need not be one device. Sum the idle draws of a room, or measure the whole house — everything nominally off, and the meter still creeping — and the same relation prices the household’s entire baseline. That whole-house reading is often the more useful entry, because it captures the devices nobody remembers to suspect, and it is the figure the reverse workflow can be checked against.
The result prices a decision, not a curiosity. A switched power strip, a timer, a habit of hard-off — each has a cost in convenience, and this page supplies the other side of that trade in currency per year. The declared reverse runs the question the other way: start from an annual amount you suspect the baseline costs, and the engine returns the continuous wattage that would explain it.
The idle draw is scaled to kilowatts and multiplied through hours per day and days per year to give annual idle energy, which the entered tariff prices; the declared reverse workflow solves for the continuous draw that produces a target annual cost.
When this calculation is used
- Pricing one device’s idle draw — from its specification sheet or a plug-through meter — before deciding whether hard-off is worth the ritual.
- Converting a measured whole-house baseline into a yearly figure, which is the number that motivates or dismisses the whole subject.
- Solving backwards — the declared reverse workflow — from a suspected annual cost to the continuous watts that would produce it, as a plausibility check on the estimate.
- Setting a purchase criterion: the difference between two products’ standby draws, annualised, is a real if small part of the cheaper-to-own question.
Worked example
Take the pack’s anchor case: a set-top box drawing 8 watts whenever it is not in use, idle 24 hours a day for all 365 days, priced at a tariff of 0.20 per kilowatt-hour.
The engine returns the year’s idle energy and its cost. Read the energy figure against a real month of household consumption from the bill page — one silent box against the meter’s total — and then remember the box is rarely alone: the honest household figure is this calculation summed over everything that glows in the dark.
Rerun with the whole house’s measured baseline in place of the single device, and the answer becomes the yearly price of the household’s entire always-on layer — the number to weigh against the actual inconvenience of switches, strips and timers.
What each input represents
Standby (idle) power draw
The watts drawn while the device is nominally off or idle — from the specification sheet, a plug-through meter, or a summed estimate across several devices. This is the idle figure, not the running draw the appliance page prices; conflating the two overstates the case for unplugging by an order of magnitude.
Hours per day on standby
How many of each day the device spends idle. The default of 24 describes the common case — plugged in around the clock — but a device that runs actively part of the day should have those hours removed here, because its active consumption belongs to a different calculation.
Days per year
The days over which the idle draw persists. The default of 365 is the honest figure for gear that is never unplugged; a holiday home, or a device genuinely disconnected for part of the year, earns a smaller number and proportionally smaller cost.
Electricity tariff
The price of one kilowatt-hour, in currency per kWh. The default is illustrative. A load spread evenly around the clock samples every time-of-use window equally, so on such plans a day-weighted average rate represents standby better than either the peak or the overnight figure.
Assumptions and limits
- The idle draw is a constant: real devices step between standby modes with different draws, and the entered figure has to stand for their average.
- One tariff prices the whole year — rate changes, seasonal pricing and time-of-use structure are averaged away by construction.
- The hours entered are genuinely idle hours; time the device spends running belongs to the appliance page, and double-counting a device across both inflates its total.
- A specification-sheet standby figure is a manufacturer’s claim under test conditions. A plug-through meter reading from your own wall outranks it whenever the two disagree.
What the guards protect against
- A zero idle draw is refused — the pack ships that refusal as a declared test vector — because a device drawing nothing has no standby cost to compute, and a silent zero would bury the commonest cause: a milliwatt figure entered in the wrong unit.
- The draw is capped at a kilowatt, an order of magnitude above any real standby: a figure that size is an active load misfiled as idle, and refusing it keeps this page from flattering a running appliance into a phantom.
- Hours per day and days per year are bounded by the calendar — no more than 24 and 366 — so a weekly or annual figure entered in the wrong field is refused as impossible duty rather than multiplied into fiction.
Provenance
Phantom-load relation, annual cost = idle watts ÷ 1000 × hours per day × days per year × tariff
The idle draw is scaled to kilowatts and multiplied through hours per day and days per year to give annual idle energy, which the entered tariff prices; the declared reverse workflow solves for the continuous draw that produces a target annual cost.
Screening and reference material, to be checked against the governing standard and a qualified engineer; not a design determination. The signed pack carries its own citation, and the page reports the verification state of the release it mounted.