How the Electricity Cost Calculator works
Last data update: 2026-08-24 (rates for May 2026).
Data
State rates come from the U.S. Energy Information Administration's Electric Power Monthly, Table 5.6.A, "Average price of electricity to ultimate customers by end-use sector, by state", residential column, data month May 2026 (released July 23, 2026). The file state-tariffs.csv holds one row for each of the 50 states and the District of Columbia, at EIA's two-decimal precision in cents per kilowatt-hour, with the data month and the source on every row. The national figure, 18.44 ¢/kWh, was read directly from EIA's Electricity Monthly Update. The state values were transcribed from two independent republications of Table 5.6.A that agree to the cent, because EIA's own table page was unavailable at collection time.
Appliance wattages come from appliance-watts.csv, the same table the generator wattage calculator uses, where every row names the manufacturer document or wattage chart its figure was taken from. The calculator uses the running watts only; starting surges do not matter for energy cost.
Household consumption reference: EIA FAQ 97 — 10,791 kWh a year, about 899 kWh a month, the 2022 figure as published at collection time.
How the state average is applied
The calculator uses one number for the whole month: the residential average for the state you pick, or the U.S. average of 18.44 ¢/kWh if you pick none. Every kilowatt-hour is charged at that rate. If you type your own rate into the override box, any positive value replaces the state average for the whole calculation, and the result says it is your override. Otherwise the result names the state, the words "EIA average" and the data month, so it is always clear which number was used.
EIA's state average folds in the fixed charges and riders on a typical bill, which is why it usually sits a little above the per-kWh number printed on yours.
Formula
kwh_day = watts / 1000 × hours × duty_cycle
cost_day = kwh_day × rate_cents / 100
cost_month = cost_day × days_per_month // default 30, range 1–31
cost_year = cost_day × 365
share = kwh_month / 899 // share of an average US home's month
Duty cycle runs from 10 % to 100 % in steps of 5, and starts at 100 %. Appliances that cycle on a thermostat or float — refrigerators, air conditioners, dehumidifiers — are flagged in the wattage table, and for those the result reminds you to lower the duty cycle.
Worked example
An 8,000 BTU window air conditioner, the LG LW8024R, is listed at 730 W ("Watts (Cooling) 730" in LG's specifications). Run for 8 hours a day at 100 % duty in Texas (16.44 ¢/kWh):
- 0.730 kW × 8 h = 5.84 kWh a day
- 5.84 kWh × 16.44 ¢ = $0.96 a day
- × 30 days = $28.80 a month (175 kWh, about 19 % of an average home's 899 kWh)
- × 365 days = $350.44 a year
At the U.S. average of 18.44 ¢ the same use costs $1.08 a day and $32.31 a month. If the compressor actually runs 60 % of those 8 hours, set the duty cycle to 60 %: 3.50 kWh a day, $17.28 a month in Texas.
What the rate leaves out
- Fixed charges: a monthly customer charge is not added as a separate line. It is present only to the extent that EIA's average folds it in.
- Tiered rates: where the price per kWh rises with monthly use, the cost of the next kilowatt-hour can be well above or below the state average.
- Time-of-use plans: the same appliance costs a different amount at different hours, and a single average cannot show that.
- Your own tariff: your utility's rate is not the state average. The override box is there for it.
Duty cycle is a user estimate, and an appliance's real draw varies with conditions; the wattage table gives a typical running figure, not a measurement of your unit.
Update cadence
The rate file is updated by hand, not automatically. The current file is the first release, collected on 2026-08-24 with May 2026 data, and it has not been refreshed since. When it is, the data month on every row, the date at the top of this page and the change log below change together.
Change log
- 2026-10-04 — methodology expanded: data scope, how the average is applied, a worked example, what the rate leaves out, update cadence. No change to the data or the formula.
- 2026-08-24 — first release; May 2026 rates.
Cite this page
GridComfort, "Appliance Electricity Cost Calculator — methodology," https://gridcomfort.com/tools/electricity-cost-calculator/methodology/, data updated 2026-08-24.