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Can a smart plug pay for itself?

Sometimes. A $15 plug that removes a real 40-watt load for 12 hours a day can repay itself in months. Put that same plug in front of a two-watt standby load and the plug may consume more electricity than the schedule saves.

I do not treat every powered device as waste. The Caséta bridge, HomeBase 3, and Home Assistant host in my house are supposed to listen, record, and automate when nobody is actively using them. Putting infrastructure like that on a timer would save electricity by removing the service I installed it to provide.

A smart plug makes financial sense only when the scheduled-off hours are genuinely disposable and the connected device returns safely and predictably.

The calculation behind the result

The plug avoids some energy while the load is off, but the plug itself remains powered all day:

Annual energy avoided = load watts × off-hours per day ÷ 1,000 × 365
Annual plug energy = plug watts × 24 ÷ 1,000 × 365
Annual net saving = (energy avoided − plug energy) × price per kWh
Payback months = plug price ÷ annual net saving × 12

The calculation assumes the same schedule and electricity price throughout the year. It does not assign money to convenience, automation, monitoring, or the time spent diagnosing a device that failed to restart.

A case where the plug pays back

Suppose a device draws 40 watts during 12 hours when it provides no useful service. Cutting those hours avoids 175.2 kWh a year. A one-watt smart plug consumes 8.76 kWh across the full year, leaving 166.44 kWh of net reduction.

At $0.20/kWh, that saves $33.29 a year. A $15 plug repays its purchase price in about 5.4 months.

Measure the state you intend to eliminate

The largest number printed on a power brick is not the input. I need the device’s actual average draw during the proposed off-hours. A computer that briefly reaches 200 watts but sleeps at three watts all night offers roughly three watts—not 200 watts—of scheduling opportunity.

I let a suitable electricity meter cover enough time to catch sleep, charging, updates, fans, heaters, and overnight cycles. For a cycling load, I use energy over several complete cycles instead of a single instant. The always-on electricity guide shows how I turn a meter’s kWh reading into average watts.

Then measure or verify the plug itself

A Wi-Fi radio, relay, processor, and power-monitoring circuit need electricity. A plug drawing one watt continuously uses 8.76 kWh per year. At the example rate, that costs $1.75. A low standby load can disappear inside that overhead.

I prefer a measured figure for the exact plug. If only a documented maximum or an unverified estimate is available, I run the calculator again with a less favorable number. A purchase that works only when the plug is assumed to consume almost nothing is not a strong energy case.

Devices I would not hard-cycle just for the arithmetic

• Storage and computers that expect an orderly shutdown. Removing power can corrupt data or turn a small saving into a recovery job.
• Routers, access points, bridges, and Home Assistant. Their idle-looking hours are often when they provide availability.
• Security equipment. A cheaper electricity bill is not a useful result if recordings or alerts disappear.
• Compressors, heaters, pumps, and chargers without a verified use case. Load type, inrush, duty cycle, and restart behavior matter.
• Anything that stays off after power returns. A schedule cannot save electricity usefully if someone must press a physical button every morning.

The plug also needs the correct electrical rating for the load. I do not assume that a relay marketed for a lamp is appropriate for a motor, heater, or high-inrush device.

Buying for Home Assistant: the details that change the result

“Works with Home Assistant” can describe very different products. Before buying, I check the exact model for:

1. Power monitoring. On/off control does not guarantee energy data.
2. Local control. I want to know whether the normal command path survives an internet outage and what setup still depends on the vendor cloud.
3. Power-on behavior. After an outage, the plug should restore the deliberate state—or use a safe default I understand.
4. Load rating. Resistive, motor, and high-inrush loads are not interchangeable.
5. Measurement quality. A power sensor is useful only if its resolution and update behavior fit the load being measured.
6. Physical fit. A bulky enclosure that blocks the second receptacle has a cost even if it does not appear in the calculator.

I verify the model rather than trusting the family name. Manufacturers sometimes sell cloud-only, energy-monitoring, non-monitoring, Wi-Fi, Thread, Zigbee, and Matter versions under nearly identical branding.

A smart plug can be worth buying without paying back

Remote control, presence simulation, energy visibility, and a deliberate way to reboot awkward equipment can all be useful. I keep those benefits separate from the electricity result because otherwise any convenient purchase can be described as a saving.

If I buy a plug to expose consumption in Home Assistant, its value may be the measurement. If I buy it to stop a charger on a schedule, its value may be convenience or battery-care policy. Neither claim requires pretending the power saving repaid the hardware.

My buy/don’t-buy check

1. The measured load during off-hours is materially larger than the plug’s own draw.
2. The device can lose power safely and returns to the intended state.
3. The exact plug is rated for the load and has the features I am buying it for.
4. The payback still makes sense with a less favorable electricity rate, schedule, or plug consumption.
5. The automation does not remove a service the household expects to remain available.

If the only positive result comes from using the product’s maximum wattage instead of measured standby draw, I do not have an energy-saving purchase yet.

Method and disclosure

The watts-to-kWh conversion follows the US Energy Information Administration’s electricity measurement guidance. The calculator performs the labeled arithmetic in the browser and does not send its inputs to this site.

Disclosure: This page contains no affiliate links and does not recommend an unverified plug model. If I add a commissioned product link after testing or identifying the exact hardware, I will label it beside the link.