Electricity cost calculator

What an appliance really costs to run

Most people know roughly what their electricity bill is; few know which devices drive it. What a space heater or dehumidifier costs to run depends on three things: how much power it draws, how long it runs, and what your utility charges during those hours.

In the billing engines we build, every kWh is tied to a price that depends on time, tier and plan. This calculator applies that logic to a single appliance.

Watts versus kWh

• Watts (W) measure power: how fast a device uses energy at a given moment. A 1,500 W microwave draws 1,500 W while it is on.
• Kilowatt-hours (kWh) measure energy: power multiplied by time. That 1,500 W microwave running for one hour uses 1.5 kWh.

Utilities bill kWh, not watts. A microwave used for minutes a day can cost less per month than a modest device that runs all day, like a second fridge in the garage.

How this calculator works

You choose an appliance preset or enter your own wattage. Presets take their power from the U.S. DOE Energy Saver appliance calculator, and their hours per day from EIA’s 2020 Residential Energy Consumption Survey (RECS) average annual use where RECS publishes it; otherwise the hours are an example to change. Then you set hours per day, days per month, your utility and rate plan, and the hour the appliance usually starts.

Energy:

kWh per month = watts ÷ 1,000 × hours per day × days per month

Cost:

cost = the year’s bill with the appliance − the year’s bill without it

The calculator adds the appliance’s kWh to a typical home in your state, starting at your chosen hour on the days it runs, and prices both bills on your plan for all 12 months, weekdays and weekends. On a flat plan, the added kWh cost a single price. On a time-of-use plan, they cost the price of the periods they fall in; on a tiered plan, the price of the tier the home’s total reaches. The calculator then reports cost per hour running, per use, per month (the year averaged over 12 months) and per year, plus the cheapest and priciest start hours.

A worked example: the space heater preset draws 1,320 W. Used 4 hours a day for 30 days, it uses 1.32 × 4 × 30 = 158.4 kWh a month. At a hypothetical $0.16/kWh that is about $25 a month. If those four hours fall in a TOU peak priced at a hypothetical $0.40/kWh, the same heater costs about $63. The only thing that changed was the clock.

Nameplate versus actual draw

The wattage printed on a label is usually a maximum, not what the appliance draws on average. Anything with a thermostat or compressor cycles on and off, and that duty cycle matters more than the label.

• Refrigerators run their compressor only part of the time. The DOE calculator lists a refrigerator at 225 W while running, but EIA’s RECS 2020 puts a household’s main refrigerator at 618 kWh a year on average, which is 618,000 Wh ÷ 8,760 hours ≈ 71 W around the clock. That is why the refrigerator preset uses 71 W for 24 hours a day. Room temperature, how full it is and how often the door opens all move your own figure.
• Air conditioners and heat pumps cycle to hold a set point. On a mild day the compressor runs part of the time; on the hottest afternoon it may run nearly continuously. Variable-speed units modulate instead of cycling, running at partial power for long periods.
• Thermostatically controlled heaters, water heaters and electric ovens draw full power only while heating, then idle.

For these devices, enter the hours the element or compressor is actually running, not the hours it is switched on. If you do not know, a plug-in meter will tell you.

Standby and phantom loads

Many devices draw power when they appear to be off: TVs, set-top boxes, consoles in “instant-on” mode, smart speakers, and anything with a clock or remote receiver. Each is small, but they add up and run around the clock: a combined 30 W of standby, for example, is 30 × 8,760 hours ÷ 1,000 ≈ 263 kWh a year. Use the calculator with 24 hours per day and the measured standby wattage to see what these cost.

Why the same appliance costs different amounts

A kWh costs very different amounts from one utility to another, and within a utility prices vary by plan. How much depends on the plan; each utility page on this site shows the exact prices.

• Time-of-use plans make the hour matter. On a plan with a 4–9 pm peak, running a dryer at 6 pm is priced at the peak rate, while the same load at 10 am or overnight is priced off-peak.
• Tiered plans charge more once monthly use passes a baseline allowance. The added kWh from a new appliance may be priced at an upper tier even if your average price looks low.
• Seasonal prices at some utilities are higher in summer, which lands directly on air conditioning. Seasons follow each utility’s own months.

This is why the calculator asks for your utility, plan and time of use instead of assuming a single national rate.

Measuring with a plug-in meter

For anything that plugs into a standard 120 V outlet, an inexpensive plug-in energy meter is the most reliable way to get real numbers. Plug the meter into the wall, plug the appliance into the meter, and leave it for a representative period: a full day for a fridge, a full week for anything with a variable schedule. Read the accumulated kWh and divide by the number of days. That daily kWh figure is more accurate than any preset.

For 240 V appliances such as dryers, water heaters and central AC, a plug-in meter will not fit. Use the nameplate and a realistic runtime, or a whole-house monitor; smart-meter data also shows jumps when large loads switch on.

Typical wattages

These are the wattages in the U.S. DOE Energy Saver appliance calculator, which the presets use. Actual draw varies by model, age and settings.

For comparison, EIA’s RECS 2020 puts average yearly use, in homes that have each one, at 618 kWh for a main refrigerator, 569 kWh for a separate freezer, 680 kWh for an electric clothes dryer and 111 kWh for a dishwasher.

Which appliances actually move a bill

In many homes a short list dominates: heating and cooling, water heating, clothes drying, and an EV or pool pump where present. They combine high wattage with long hours. In RECS 2020, homes with an electric water heater used 2,705 kWh a year on it on average, and homes with a pool pump 2,383 kWh, against 111 kWh for a dishwasher. Lighting and electronics matter far less, especially after a switch to LEDs.

If you want to lower a bill, start with the devices that are both high-wattage and long-running, then check whether they run during expensive hours. Shifting the dishwasher, dryer or pool pump outside a TOU peak is often worth more than replacing a small appliance.

Frequently asked questions

Why does my result differ from the appliance’s EnergyGuide label?

EnergyGuide labels use a standardized test and a national average price. The calculator uses your utility’s rate and your hours, so the dollar figure differs even when kWh are similar.

Should I use the nameplate wattage?

Only as an upper bound. For anything with a thermostat or compressor, average draw can be much lower: 71 W on average for a refrigerator from RECS, against 225 W while running in the DOE calculator. Measure with a plug-in meter when you can.

Does leaving a charger plugged in cost much?

A modern phone charger with nothing attached draws very little. Older adapters and devices with network standby draw more and are worth checking with a plug-in meter.

Why does the time of day change the cost on my plan?

On a time-of-use plan, prices differ by period, and the calculator places the appliance’s kWh in the hours starting at your chosen time. Moving use outside the peak lowers the cost; the results show the cheapest start hour.