Phantom Load Calculator

How to use the phantom load calculator

Enter how many always-plugged devices you have, the average standby watts each one draws while “off,” and your electricity rate, and you get the dollars those devices cost you a year just sitting there — plus the kilowatt-hours behind that number and the monthly figure. The point of the calculation is that standby runs around the clock: a device left on standby is assumed to draw its trickle 24 hours a day, 365 days a year, so even a couple of watts turns into a real line on the bill.

Start by counting the devices that never truly switch off. Walk a room at a time and tally anything that stays plugged in and warm to the touch, shows a clock or a standby light, or wakes the instant you hit a button — TVs, set-top and DVR boxes, game consoles, the microwave and coffee maker with their glowing clocks, and chargers left in the wall with nothing attached. The default of 10 devices is a fair count for one household, but most homes have more than people expect once they actually look.

Then estimate the average standby draw per device. Modern gear sips anywhere from a fraction of a watt to several watts on standby, and the default of 3 watts is a reasonable middle for a mixed bag of electronics. Older equipment and always-listening or “instant-on” devices tend to sit at the high end; a phone charger with nothing plugged in sits near the bottom. You are entering one average across all the devices you counted, so lean a little higher if your tally skews toward big AV gear and consoles.

The rate is the input that varies most, so use your own. The US residential average is about 17.5¢/kWh as of 2026, but it varies widely by state, so use your own bill’s rate. Add the per-kWh supply and delivery line items together, or divide a full month’s total by the kilowatt-hours used, and enter that figure — the dollar cost moves up or down in step with it, so an honest rate gives an honest answer.

Read the result three ways. The annual cost is the headline — what this standby draw quietly adds to a year of bills. The kWh figure is the same thing free of any rate assumption, handy if you want to compare against the rest of your usage. The monthly figure scales it down to bill-sized terms. Because standby is assumed 24/7, the number is a steady, every-year cost rather than a one-off, which is exactly why a few watts left on all year are worth switching off.

The formula

Standby power is just watts that never turn off, turned into energy and then into money. Take the watts each device draws, turn them into kilowatts by dividing by 1,000, multiply by the number of devices and by every hour of the year — 24 hours across 365 days — to get the energy, then multiply by your rate to get the cost:

kWh per year = devices × (standby watts ÷ 1000) × 24 × 365
annual cost = kWh per year × rate

Worked example with the defaults — 10 devices × (3 ÷ 1000 = 0.003 kW) × 24 × 365 = 262.8 kWh a year; × $0.175 = about $45.99 a year, which is roughly $45.99 ÷ 12 ≈ $3.83 a month. Scale it up and it bites harder: 20 devices at 5 W each is 876 kWh a year, about $153.30.

The usual offenders are TVs, game consoles, cable and DVR boxes, phone and laptop chargers left plugged in, microwaves and coffee makers with clocks, and “instant-on” devices that stay half-awake to respond fast. A smart power strip helps by cutting power to the devices that gain nothing from standby while leaving the ones that need it alone. Added up across a home, phantom load is commonly cited as roughly 5–10% of an electricity bill — a useful general range rather than a precise figure, since it depends entirely on what you own and leave plugged in.

Frequently asked questions