How we calculate running costs
The formula
cost = watts × hours × duty cycle ÷ 1,000 × cents per kWh ÷ 100
- Per hour is one hour of running.
- Per day is a day the appliance is used for its typical hours.
- Per month is an average month of 30.42 days (365 ÷ 12), scaled by days of use per week. For seasonal appliances (heaters, fans, dehumidifiers) it is a month in season.
- Per year counts only the months in season, with average month lengths.
- Duty cycle is the share of time a thermostat keeps the element on. A 1,400 W iron cycling half the time averages 700 W.
- Always-on appliances (refrigerators and freezers) use typical annual consumption from ENERGY STAR instead of watts × 24 hours, which would overstate them several times over.
Electricity rates
We use the EIA's average retail price of electricity to residential customers for each state and the US: total residential revenue divided by kWh sold, across all utilities, published monthly in the Electric Power Monthly (Table 5.6.A) and the EIA Open Data API. The latest month is June 2026. The EIA publishes with a lag of about two months. Year-over-year changes compare with the same month a year earlier because prices are seasonal. Annual history comes from EIA Form 861 (residential revenue ÷ residential sales for bundled and energy-only service).
Your own rate can differ: tiered and time-of-use plans, fixed monthly charges and your utility all move it. If you know your rate, use the calculator.
Electric cars
- Per mile and per month use the EPA combined rating in kWh per 100 miles. EPA measures that energy at the wall, so charging losses are already included and we do not add them again.
- A full charge uses battery capacity ÷ 90% charging efficiency when the capacity is known; otherwise the energy to drive the full EPA range.
- A month is 1,000 miles.
- Gasoline comparison: a 30 mpg car at the AAA national average price for regular. The 30 mpg figure is our round-number assumption, not a measured average.
Usage assumptions for each appliance
Hours a day and seasons are our assumptions for a typical household. Watts and annual kWh come from the sources listed on each page; where a source gives only a range, we use the midpoint.
| Appliance | Power or energy | Typical use we assume |
|---|---|---|
| Space heater | 1,500 W | 8 hours a day on its high setting, November to March |
| Ceiling fan | 120 W | 8 hours a day, May to September |
| Whole-house fan | 495 W | 6 hours a day in the evening, May to September |
| Dehumidifier | 785 W | 12 hours a day of running time, May to September |
| Electric blanket | 100 W | 8 hours a night at full power (double size), November to March |
| Refrigerator | 397 kWh/yr | plugged in all year, using the ENERGY STAR typical annual consumption |
| Chest freezer | 215 kWh/yr | plugged in all year, using the ENERGY STAR typical annual consumption |
| Upright freezer | 395 kWh/yr | plugged in all year, using the ENERGY STAR typical annual consumption |
| Electric oven | 1,804 W | 1 hour a day of cooking |
| Microwave | 925 W | 15 minutes a day |
| Dishwasher | 1,800 W | one 1-hour cycle, 5 days a week |
| Coffee maker | 900 W | 30 minutes a day, including the warming plate |
| Toaster | 1,100 W | 6 minutes a day |
| Toaster oven | 1,225 W | 30 minutes a day |
| Washing machine | 400 W | one 1-hour load, 4 days a week (motor only) |
| Clothes dryer | 3,400 W | one 1-hour load, 4 days a week |
| Clothes iron | 1,400 W | 30 minutes, twice a week, with the thermostat cycling about half the time |
| TV | 120 W | 5 hours a day |
| Desktop computer | 120 W | 8 hours a day (tower only, no monitor) |
| Laptop | 50 W | 8 hours a day while plugged in |
| Computer monitor | 150 W | 8 hours a day |
| Electric water heater | 5,000 W | 3 hours a day of element heating time (tank type) |
| Hair dryer | 1,540 W | 15 minutes a day |
| Well pump | 675 W | 1 hour a day of pumping |
| Vacuum cleaner | 1,220 W | 1 hour a week |
Rounding
We calculate with full precision and round only for display: headline amounts of $10 or more to whole dollars, smaller amounts to the cent, rates to a tenth of a cent. Totals in tables may not add up exactly.
Which pages are indexed
A page is only offered to search engines when it has every element we promise: costs, scenarios, state comparison, a year-over-year change, a sourced wattage, tips, answers and related links. Pages missing any of these stay available to visitors but are marked noindex.