Electricity Cost Calculator

How it works

Utilities bill energy in kilowatt-hours: one kWh is 1,000 watts running for one hour. Multiplying an appliance's watts by the hours it runs each day and dividing by 1,000 gives its daily kWh. Multiplying by the days it is used gives the monthly kWh.

Cost is energy times price. Your rate is on your bill in cents per kWh; the calculator converts it to dollars and multiplies. The yearly figure is simply twelve times the month you described, so it assumes the same usage pattern all year.

The result tells you what a habit costs. A 1,500 W space heater for three hours a night is a different decision from a 10 W LED strip left on all day, and the monthly figure makes that comparison concrete.

Formula

kWh per day   = watts × hours per day ÷ 1,000
kWh per month = kWh per day × days per month
cost per day  = kWh per day × rate ÷ 100
cost per month = kWh per month × rate ÷ 100
cost per year = cost per month × 12

Example

A 1,500 W space heater running 3 hours a day uses 1,500 × 3 ÷ 1,000 = 4.5 kWh per day. Over 30 days that is 135 kWh.

At 16 ¢ per kWh the heater costs $0.72 a day, $21.60 a month and, if that continued all year, $259.20.

Assumptions and limitations

• The appliance is assumed to draw its rated watts the whole time it is on. Heaters, air conditioners and refrigerators cycle on and off under thermostat control, so their average draw is lower than the nameplate; enter the hours the element actually runs, or use the yearly kWh printed on the energy label.
• The rate is a single flat price per kWh. Time-of-use and tiered tariffs, fixed monthly charges, taxes and delivery fees are not modelled, so the all-in rate on your bill may be higher than the headline energy rate you entered.
• The yearly figure is twelve identical months, not a seasonal profile.
• A calculation is not code compliance. Whether a circuit can safely supply an appliance is governed by the National Electrical Code (NEC) and local amendments; consult them and a licensed electrician before adding or changing wiring.

Frequently asked questions