There is no single monthly price for running a home NAS: the answer depends on its average power draw, how many hours it runs, and your electricity rate. For continuous operation, multiply average watts by 8.76 to get annual kilowatt-hours, then multiply by your price per kWh. As a clearly qualified example, a Synology DS423’s published 32.41 W Access-state figure would cost about $49 a year, or $4.09 a month, if sustained around the clock at the 2025 U.S. average residential rate of 17.30¢/kWh. That is a calculation from a manufacturer specification, not a measured annual bill for every DS423.
How to calculate the electricity cost of a NAS
Your electricity bill charges for energy used over time, in kilowatt-hours (kWh), not for the NAS’s wattage by itself. Watts describe power at a moment; kWh describe accumulated use. For a NAS that runs continuously at a reasonably steady average power, use:
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Annual energy (kWh) = average power (W) × 8.76
Annual cost = annual energy (kWh) × electricity price per kWh
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The factor 8.76 combines 8,760 hours in a 365-day year with the conversion from watts to kilowatts. Put the electricity price into the same currency and units shown on your bill. For example, a price of 17.30¢/kWh is $0.173/kWh; multiply kWh by 0.173 to get dollars.
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As a quick reference, each continuously used watt amounts to 8.76 kWh a year. Multiply that by your own per-kWh price to find the annual cost of each watt. This makes it easy to compare a measured 10 W average with a 20 W average without confusing either figure with a monthly bill.
When power changes, use a weighted average
A NAS may draw different amounts in different states. If you know the time spent in each state, calculate the average power by weighting each state’s wattage by its share of the hours. For two states, the calculation is:
Average watts = (state 1 watts × hours in state 1 + state 2 watts × hours in state 2) ÷ total hours
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Then apply the annual-energy and cost formulas to that average. The resulting estimate is only as representative as the states and time shares you put into it. A figure for one particular operating state should not be treated as the whole-year average unless the NAS actually spends all, or nearly all, of its time there.
What the Synology DS423 example costs
Synology publishes two power-consumption figures for its four-bay DiskStation DS423: 32.41 W in the Access state and 4.97 W in HDD Hibernation. They illustrate how much the answer can change with operating state, but they are manufacturer specifications for defined test conditions, not measurements of a household’s particular unit and drive configuration.
| DS423 state or price reference | Power or electricity rate | Calculated energy and electricity cost | What the figure means |
|---|---|---|---|
| Access state, continuous operation | 32.41 W; 17.30¢/kWh | About 284 kWh/year; about $49/year or $4.09/month | Access-state specification from Synology, calculated as if that power were sustained all year; cost uses the EIA’s 2025 U.S. average residential price. |
| HDD Hibernation, continuous operation | 4.97 W; 17.30¢/kWh | About 43.5 kWh/year; about $7.53/year or $0.63/month | HDD Hibernation specification from Synology, calculated as if the NAS remained in that state all year; it is not a typical-use estimate. |
| Access state, continuous operation | 32.41 W; 18.21¢/kWh | About 284 kWh/year; about $52/year or $4.32/month | Same sustained-power illustration using the EIA’s 2026 U.S. residential-price outlook, which is a forecast rather than a final observed annual average. |
For the first row, 32.41 × 8.76 is about 284 kWh/year; 284 × $0.173 is about $49/year. Dividing by 12 gives an average of roughly $4.09 per month. The 2026 outlook changes the rate used in the multiplication, not the assumed power draw.
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Synology describes its hibernation measurement as one in which the device under test is measured while all hard drives are in low-power mode. That explains what the 4.97 W figure represents; it does not mean a NAS will always enter hibernation or stay there in normal use. The $7.53 annual illustration is therefore not a promise of what an owner will pay.
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- Measure the complete setup at the wall. Measure the NAS together with its installed drives and any equipment you want included in the estimate. A whole-system wall reading is more useful than a component rating because it reflects the power actually drawn by the assembled setup.
- Collect readings during representative use. A momentary reading may not capture changes caused by access or idle periods. Measure over representative days or weeks that include the household’s normal workload, such as the times you use the NAS for backups or media serving. Do not label a brief low reading as a year-round average if the device’s routine is different.
- Record the time pattern. If the NAS runs continuously, use your measured average watts directly. If it is scheduled to shut down or you can distinguish operating states, include the hours spent in each state and the hours it is off. A lower duty cycle reduces the time it consumes electricity, but also means the NAS is unavailable during shutdown.
- Find the applicable electricity price. Use the rate that applies to your home rather than assuming a national average. Where relevant, use the all-in marginal cost of an additional kWh, including applicable delivery charges; your bill or utility tariff is the place to check the rate and how it is presented.
- Do the arithmetic and keep the assumptions with the result. For continuous use, calculate watts × 8.76 × dollars per kWh. Divide by 12 for a monthly average. Write down the measurement period, workload, installed drives, operating schedule and rate alongside the result so you can tell later what the estimate covers.
Suppose a whole-system measurement produces an average of W watts and the applicable rate is R dollars per kWh. The annual estimate is W × 8.76 × R dollars, and the monthly average is that amount divided by 12. This form is deliberately left in variables: a household-specific answer requires its own measured average and tariff.
Why your actual cost may differ from a model’s published figure
Access and low-power states are not interchangeable
The DS423’s listed Access and HDD Hibernation readings are substantially different. Which one better reflects your bill depends on how much time the NAS spends in each state. Background indexing, media serving, backups, containers and frequent access are possible reasons the system may not remain in a low-power state; their effect is not quantified by the cited figures. Treat them as workload factors to observe, not as a universal wattage adjustment.
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Hibernation can reduce the time drives spend active, but a low-power specification is not automatically the right target for every household. A NAS configured to be available for a service or a backup schedule may need to stay ready or wake when used. Estimate the behavior you need rather than assuming the lowest published state describes normal operation.
Drive count, drive type and connected equipment matter
A vendor’s test specification applies to its stated test configuration. A different number or type of installed drives can change whole-system consumption, as can attached devices included in the measurement. The product figure is useful as a model-specific reference point; it is not a guarantee for a differently configured NAS. Measure the setup you actually plan to run when a household-specific estimate matters.
A power-supply rating is not a consumption reading
The wattage printed on a power supply describes its rating or capacity, not the amount the NAS draws continuously from the wall. Do not multiply a PSU’s maximum rating by 8.76 and call the result your annual electricity cost. Use a whole-system wall measurement or a clearly identified vendor consumption figure instead.
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Operating hours change the total
The continuous-operation formula assumes 8,760 powered hours in a 365-day year. If you schedule shutdowns, the NAS has fewer operating hours and its annual electricity use falls accordingly; if its power varies while on, account for the different states as well. The trade-off is access: shared files, scheduled backups and other NAS-dependent tasks cannot rely on the device while it is off. Choose a schedule based on availability needs, not only on the lower energy total.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Which electricity price should you use?
The EIA reported a 2025 U.S. average residential electricity price of 17.30¢/kWh. Its October 2026 short-term outlook gives 18.21¢/kWh as an estimate for 2026. The latter is a forecast, not a final observed annual average. Both figures are national reference points; neither is a substitute for the price that applies to an individual home.
Local rates can differ, and a bill may show multiple components. For an estimate of the additional electricity cost of the NAS, use the applicable marginal rate for another kWh, including relevant delivery charges where they apply. If your rate changes by time of day or under another tariff condition, the most representative estimate would account for when the NAS runs and the rate in those periods. The simple formula assumes one price per kWh.
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What this estimate includes—and what it leaves out
The calculation above covers electricity for the equipment included in the measurement. It does not include the NAS purchase price, replacement drives, networking gear that was not part of the measurement, cooling, or the value of having data available. Those expenses may matter to the total cost of owning a NAS, but they are separate from the electricity-only answer and should not be folded into it without stating the added assumptions.
For a fair comparison between two setups, use the same workload and measurement approach, compare whole-system average wall power, note the installed drive count and type, account for actual powered hours, and apply the same household tariff. A difference in annual electricity cost is meaningful only if those assumptions are comparable. Capacity, noise, backup behavior, purchase price and availability are separate decision factors rather than electricity measurements.
The practical takeaway
To estimate what a home NAS costs to run, measure its average whole-system wall power during representative use, multiply the watts by 8.76 for annual kWh if it runs continuously, and apply your own electricity rate. Treat manufacturer figures such as the DS423’s Access and HDD Hibernation readings as state-specific reference points, not as a substitute for your household’s actual operating pattern. The bill estimate is only as precise as those inputs.
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