FIELD GUIDE 01
How to calculate the true electricity cost of an appliance
A useful estimate starts with reliable energy use, the part of your electricity rate that changes, costs you have not yet paid, two options that do the same job, and a realistic ownership period. This guide shows how they fit together—and where quick calculations usually go wrong.
01 / THE CORE FORMULA
Convert watts into annual cost
Watts measure power at an instant. Utility bills charge for energy over time in kilowatt-hours. Divide watts by 1,000, multiply by active hours, then multiply by the price per kilowatt-hour.
For example, a 1,500-watt heater used four hours per day consumes 2,190 kWh per year. At the EIA 2026-05 national residential average of 18.44¢/kWh, that is about $403.84 per year.
02 / YOUR ELECTRICITY RATE
Use the part of the bill that changes
Look for the variable rate: the amount charged for each additional kilowatt-hour. If your bill does not show one rate, divide the variable energy charges by the billed kWh.
Energy charges, supply charges, and per-kWh delivery charges that rise with consumption.
Monthly customer charges and other fixed fees that remain the same when usage changes.
Time-of-use plans. Run separate scenarios for peak and off-peak operation when timing can change.
State averages are useful for a first estimate, but they will not reproduce your bill. Start with an EIA residential average, then replace it with your own rate when you have it.
03 / DUTY CYCLE
Scheduled time is not always active time
A refrigerator is plugged in all day but its compressor cycles. An air conditioner may be scheduled for eight hours while actively cooling for only part of that window. Duty cycle expresses that active share as a percentage.
Active hours = scheduled hours × duty cycle. Eight scheduled hours at a 60% duty cycle equals 4.8 active hours. For devices with highly variable loads, a plug-in energy meter or the product’s annual EnergyGuide estimate is usually better than guessing.
04 / PURCHASE COMPARISONS
Compare costs from today—not sunk costs
If you are deciding whether to keep equipment you already own, its purchase price is usually a sunk cost and the current option begins at $0. If replacement is unavoidable, compare the proposed option with the standard option you would otherwise buy. Include installation and subtract only confirmed rebates or resale value.
Only interpret payback after confirming both options provide comparable capacity, output, workload, and required features. Then compare payback with the years you realistically expect to own the option. A seven-year payback does not support a five-year ownership decision.
Compare two scenarios →05 / COMMON QUESTIONS
Questions worth asking before trusting the result
Why does my bill rate differ from the state average?
EIA figures are statewide residential averages. Your utility, tariff, fuel adjustments, taxes, fixed charges, and time-of-use periods can make your bill different. Use the variable energy rate from your bill when accuracy matters.
Should I use watts or annual kWh?
Use annual kWh when an EnergyGuide label or measured yearly total is available. Use watts and operating time when you are estimating a device or habit from its power draw.
What is duty cycle?
Duty cycle is the share of scheduled time that equipment actively draws its stated power. A compressor that runs for half of an eight-hour window has a 50% duty cycle.
Does the calculator include fixed utility fees?
No. Fixed customer charges generally do not change when one appliance uses less energy, so the lab deliberately compares variable electricity cost.
Is simple payback the same as total return?
No. Simple payback divides extra upfront cost by annual savings. It does not model financing, maintenance, rebates, equipment life, or future electricity-price changes.
Reference rates: U.S. EIA Electric Power Monthly, residential retail sales. The calculator is a planning tool, not a utility-bill prediction or professional financial recommendation.