Compare equipment allocation, recurring services and electricity over the same period. Use watts × operating hours ÷ 1,000 for kWh, then apply your own tariff.
Separate the costs
A device price and a monthly subscription price describe different things. To compare a small system, separate the initial purchase, recurring services, electricity, and maintenance effort. This makes the comparison useful even when one option has no monthly hosting bill.
Our running-cost calculator spreads equipment cost over a user-selected number of months, then adds hosting, software, and estimated electricity. The equipment amount is a planning allocation, not an accounting depreciation schedule. A device you already own may have no new cash purchase cost, but replacing it or using it for another job is still worth considering.
Calculate energy use
Energy in kilowatt-hours equals watts multiplied by operating hours, divided by 1,000. For a monthly pattern, multiply by the number of operating days as well. The US Department of Energy presents the same unit relationship in its home energy education material.
For an illustrative 8-watt device operating 24 hours a day over 30 days, the result is 5.76 kWh. At an example rate of 0.20 per kWh, its electricity amount is 1.152 in that currency. Neither the wattage nor the price is a claim about your device or electricity tariff.
Use measured average power for a representative workload when available. A power adapter’s maximum rating is not a measurement of the device’s average consumption.
Compare matching assumptions
Hold the workload, expected availability, storage, backups, and time window constant when comparing options. Otherwise, the cheaper amount may simply describe a different service. Include the fees you know about, and keep an explicit list of omitted items such as network upgrades or replacement storage.
If hardware costs 120 and the planning life is 24 months, the monthly equipment allocation is 5. Add 5 for hosting, 0 for software, and the example 1.152 electricity amount: the result is 11.152 per month, displayed as 11.15. Annualization multiplies that monthly pattern by 12; it does not predict seasonal usage or tariff changes.
Keep effort in the picture
A low recurring cash amount can come with setup, updates, monitoring, and recovery work. Record maintenance time separately rather than pretending it is free. Decide whether a self-managed option fits the time and reliability you need, not only the calculator total.
Use the running-cost calculator with your own figures, then export the comparison. The examples are for planning; reconcile an actual bill or purchase against its own terms and measurements.