How the running-cost calculator works
Every cost on this site comes from the U.S. Department of Energy formula: daily kWh = (watts ÷ 1000) × hours per day, then cost = daily kWh × days × price per kWh. The default rate is the US residential average of 18.56¢/kWh (March 2026, EIA), and you can swap in your own state or exact rate. It's deliberately simple and transparent — no hidden adjustments.
Source: U.S. DOE — Estimating Appliance and Home Electronic Energy Use.
The formula, step by step
1. daily kWh = (watts ÷ 1000) × hours per day
2. cost = daily kWh × days × (¢ per kWh ÷ 100)
Worked example: a 1,500 W space heater for 8 hours a day → (1500 ÷ 1000) × 8 = 12 kWh/day. Over 30 days that's 360 kWh, and at 18.56¢/kWh it costs 360 × 0.1856 ≈ $67/month.
Appliances that cycle
A refrigerator, freezer, air conditioner or heat pump doesn't run at its nameplate wattage the whole time — it cycles on and off. For those we use a published annual-kWh figure or a realistic average wattage, so the estimate matches real running rather than peak draw. The methodology lists every assumption and source.
Frequently asked questions
What formula does the running-cost calculator use?
The U.S. Department of Energy formula: daily kWh = (watts ÷ 1000) × hours per day; cost = daily kWh × days × price per kWh. It's the same maths DOE uses in its own appliance energy examples.
Is the calculator accurate?
It is exactly as accurate as your inputs. Use your appliance's real nameplate wattage and your bill's effective rate for the most accurate result. The default wattages are typical DOE/ENERGY STAR figures, and many appliances cycle, so treat results as solid estimates.
Does it account for appliances that cycle on and off?
For devices that cycle (fridge, freezer, AC, heat pump), we use an annual-kWh figure or an average wattage rather than the peak nameplate watts, so the estimate reflects real running, not the maximum draw.
Keep learning
Last updated: 2026-06-20