How the estimate works
Energy in kWh = watts ÷ 1,000 × hours per day × days. Cost = kWh × your price per kWh. For example, 1,000 watts running four hours a day for 30 days uses 120 kWh. At $0.18/kWh, the energy charge is $21.60.
Compare equal light output
Match lumens, not watts, when considering a replacement. This example compares a 60-watt bulb with a 9-watt bulb for five hours per day. At $0.18/kWh over 30 days, the electricity difference is $1.38 per bulb. Purchase price, lamp compatibility and actual life are separate considerations.
What this estimate leaves out
The calculator uses constant power and a single electricity rate. It does not model startup surges, changing settings, tiered rates, demand charges, taxes, or fixed account fees. Enter average measured watts when possible. Use a separate calculation for each time-of-use rate period. All amounts are in U.S. dollars.
Common questions
Does leaving it plugged in mean it uses full power?
No. Standby and active power differ. Use measured consumption or the correct operating mode rather than assuming full rated power continuously.
Can I use my total bill divided by kWh?
That gives an effective whole-bill average. It can overstate the additional cost of an appliance if your bill includes fixed fees. For incremental running costs, use the variable per-kWh charges.
Calculation sources
U.S. Department of Energy: Electricity 101 · DOE energy education: kWh formula
Published September 17, 2026. Formulas are shown so you can check the arithmetic. Examples are illustrative and are not appliance testing results.
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