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CostORun

Methodology

Calculation Formula

The running cost formula:

Step 1: kWh = (Watts × Hours per day) / 1000

Step 2: Daily cost = kWh × Rate ($/kWh)

Step 3: Monthly cost = Daily cost × 30 days

Step 4: Annual cost = Daily cost × 365 days

This is the standard formula used by utilities, the Department of Energy, and ENERGY STAR for calculating appliance operating costs.

Data Sources

Electricity Rates

State and national average rates come from the U.S. Energy Information Administration (EIA), the official statistical agency of the U.S. Department of Energy.

  • • EIA Table 5.6.A — Average Retail Price of Electricity by State
  • • EIA Open Data API — Automated monthly updates
  • • Data represents residential sector average rates

Appliance Wattage

Typical wattage values reference U.S. Department of Energy guidelines and manufacturer specifications.

Usage Estimates

Default hours-per-day values represent typical U.S. household usage patterns based on DOE research.

  • • Always-on appliances use duty cycle estimates (e.g., refrigerators ~8-12 hours effective runtime)
  • • Seasonal appliances use regional climate data
  • • All defaults are editable in our calculators

Limitations & Disclaimers

  • ⚠ State averages only: Your actual rate may differ. Check your utility bill for exact rates. Time-of-use pricing, demand charges, and tiered rates are not modeled.
  • ⚠ Typical wattage: Actual power draw varies by model, age, settings, and conditions. Use a plug-in energy meter (like Kill A Watt) for precise measurements.
  • ⚠ Estimates only: Results are educational approximations. For billing disputes or energy audits, consult your utility provider.

Update Schedule

Data Type Update Frequency Source
Electricity rates Monthly EIA Open Data API
Appliance wattage Quarterly DOE, ENERGY STAR, manufacturers
Usage patterns Annually DOE residential surveys

Last updated: 2026-03-26
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