Electricity Cost Calculator

What this calculator does

Every appliance in the house has a running cost, and almost nobody knows any of them — which is why the space heater surprise lands on so many January bills. The math is one line: watts to kilowatts, times hours, times your rate. This calculator adds the two corrections that keep the estimate honest — the duty cycle, and your real electricity rate rather than the advertised one.

The arithmetic

kWh per day  = watts ÷ 1,000 × hours on × duty cycle
cost per day = kWh × rate

A 1,500-watt space heater running eight hours a day at a 17¢ all-in rate:

• 1.5 kW × 8 h = 12 kWh a day
• 12 × $0.17 = $2.04 a day — about $62 a month while it is in use

That is the calculation people wish they had run in October. The same arithmetic prices anything with a nameplate, from a 10-watt router (about a dollar a month, always on) to a 5,000-watt dryer load.

Your real rate is not the advertised rate

Utility marketing quotes the supply rate. Your bill adds delivery charges, riders, fuel adjustments and taxes, and the all-in figure is routinely 30–50% higher than the headline number.

The honest rate takes one division: total bill ÷ kWh used, both printed on every statement. That is the number to put in the calculator, because every kWh you save avoids the whole stack, not just the supply portion. State averages — the EIA publishes them — range from around a dime to over forty cents, so a national average is nearly useless for your house.

Duty cycle: why the fridge is cheaper than it looks

Nameplate wattage is a maximum draw, and appliances split into two families:

• Resistive, always-on loads — heaters mid-blast, incandescent lights, fans — draw their rating whenever on. Duty cycle 100%.
• Cycling loads — refrigerators, AC, thermostat-controlled heaters — run their compressor or element intermittently. A fridge is “on” 24 hours and drawing real power for perhaps a third of them.

Ignoring duty cycle is how estimates for fridges and AC come out double or triple reality. Setting it right — 30–50% for most cycling appliances — is the difference between an estimate and a scare story. Better yet, a plug-in kWh meter for a day measures the truth, cycling included, and costs less than most of the errors it prevents.

Where the money actually is

Ranked by what moves a US bill, not by folklore:

1. Heating and cooling dominate — which is why attic insulation is an energy decision wearing a home-improvement costume, and the insulation calculator is the companion tool.
2. Water heating is second in most homes.
3. The always-on layer — fridge, freezer, router, standby trickle — matters because it runs 8,760 hours a year. Twenty watts of standby is ~175 kWh annually, real money at coastal rates.
4. Lights and electronics are mostly small, post-LED. The device folklore worries about — the phone charger — costs pennies a year.

The pattern: cost = watts × hours, and the hours term is where intuition fails. A big draw used briefly (kettle, microwave) is cheap; a modest draw used constantly is not.

Budgeting with the number

The per-month figure slots straight into a budget’s needs bucket — the 50/30/20 calculator is the frame — and the per-year figure is the one to hold against an appliance upgrade. A new refrigerator that saves 300 kWh a year is worth about $50 annually at 17¢: fine as a tiebreaker, rarely a reason to replace a working machine. Seasonal loads deserve the same annualising treatment as the commute cost calculator gives driving — a $62 heater month is really a $250 winter, and naming it is what makes the thermostat argument concrete.

For methodology and typical wattages by appliance, the Department of Energy’s estimation guide is the primary source this page’s method follows.