Estimate how much an appliance or set of matching appliances adds to your electric bill.
Table of contents
How to use our Home Energy Cost Calculator
- Choose What information do you have?: use Power and daily use when you know watts and daily hours, or EnergyGuide yearly use when you have kWh per year from a label.
- Enter the appliance numbers: Appliance power and Use time, or Yearly energy use, plus Electricity price and Number of same appliances.
- Open Advanced options only if needed, then adjust Active time for appliances that cycle on and off or Bill month length to match your billing period.
- Select Calculate and read Estimated yearly cost first, then use Estimated bill-month cost and Bill-month energy used to compare with your electric bill.
- Sanity-check the result: a small Estimated daily cost can still create a noticeable Estimated yearly cost, and Bill-month energy used should be only part of your total home kWh unless you are measuring many appliances.
Definitions
Appliance power: The rate at which the appliance uses electricity, entered in watts. Watts measure power at a moment in time [1].
Use time: The average number of hours per day the appliance is on or available to run.
Yearly energy use: The kWh per year value from an EnergyGuide label or product sheet for one appliance.
kWh: Kilowatt-hour, the amount of energy used by 1 kilowatt running for 1 hour. Electric bills usually track energy in kWh.
Electricity price: The cost per kWh. Use your own bill when possible because the total price may include supply, delivery, and fees.
Active time: The percent of the Use time when the appliance is actually drawing the entered Appliance power.
Bill month length: The number of days in the billing period used for Estimated bill-month cost and Bill-month energy used.
Common mistakes and quick fixes
Mistake: Entering amps or volts in Appliance power instead of watts.
Fix: Use watts for Appliance power, or multiply amps by volts before entering the value.
Mistake: Using the total time owned for Use time instead of average hours per day.
Fix: Enter the average daily on-time in Use time, from 0 to 24 hours per day.
Mistake: Leaving Electricity price at the default when your bill has a different rate.
Fix: Use your bill for Electricity price, ideally total electric charges divided by total kWh used.
Mistake: Putting one appliance in Number of same appliances when you are estimating several identical lights, fans, or chargers.
Fix: Enter the count in Number of same appliances so energy and cost are multiplied correctly.
Mistake: Using Appliance power and Active time while What information do you have? is set to EnergyGuide yearly use.
Fix: Switch What information do you have? to Power and daily use, or enter the label value in Yearly energy use.
Mistake: Setting Active time to 100 for an appliance that cycles, such as a refrigerator, pump, heater, or air conditioner.
Fix: Lower Active time if the appliance is only drawing its listed power for part of the Use time.
Limitations & Key Assumptions / Boundary Conditions
- The estimate uses your entered Electricity price. It does not fetch local live rates, time-of-use prices, minimum charges, or taxes.
- Power and daily use mode assumes the entered Appliance power is steady during Active time. Real appliances can draw more at startup or change power by setting.
- EnergyGuide yearly use mode treats the Yearly energy use value as evenly spread across 365 days. Actual use can vary by season, household habits, and appliance settings.
- Estimated bill-month cost follows the entered Bill month length, while Estimated yearly cost always uses 365 days.
- Number of same appliances should be used only for matching appliances with the same use pattern. Different appliances should be calculated separately.
- Solar credits, battery use, demand charges, tiered rates, and smart-meter billing rules are not modeled.
Methodology
Calculation steps
The calculator uses one of two paths. In Power and daily use mode, it converts watts to kilowatts by dividing by 1000, then multiplies by time, Active time, and Number of same appliances. A kilowatt is 1000 watts [1].
daily_kwh = (power_watts * (active_percent / 100) * hours_per_day * quantity) / 1000
Then it turns daily energy into bill-month and yearly energy.
monthly_kwh = daily_kwh * days_per_month
yearly_kwh = daily_kwh * 365
In EnergyGuide yearly use mode, the calculator starts with the label's yearly kWh value for one appliance and multiplies by Number of same appliances. EnergyGuide labels are meant to help compare appliance energy use and operating cost estimates [3].
yearly_kwh = annual_kwh * quantity
daily_kwh = yearly_kwh / 365
monthly_kwh = daily_kwh * days_per_month
Cost is energy multiplied by Electricity price.
daily_cost = daily_kwh * electricity_rate
monthly_cost = monthly_kwh * electricity_rate
annual_cost = yearly_kwh * electricity_rate
Worked example
For one 1000 watt appliance used 3 hours per day at $0.17 per kWh with Active time set to 100 percent, daily energy is (1000 * 1 * 3 * 1) / 1000 = 3 kWh. With a 30.4375 day bill month, bill-month energy is 91.3125 kWh. Yearly energy is 1095 kWh. The estimated costs are $0.51 per day, about $15.52 per bill month, and $186.15 per year.