⚡ Electricity Cost Calculator

How to Use This Calculator

Enter the device's wattage, daily hours of use, and your electricity rate in cents per kWh, then hit Calculate Cost. The headline is the monthly dollar cost; the details show monthly kWh, daily cost, yearly cost, and the cost per hour of use. The default 18-cent rate matches the recent US residential average, but state rates span from about 12 to nearly 40 cents, so your bill's rate is the only one that matters for real decisions. Find it on your bill as the "supply" or "energy" charge per kWh.

The Method: Three Multiplications

The kilowatt-hour bundles power and time into the unit utilities bill, so the math is just unit conversion followed by multiplication. The worked example shows a 100-watt bulb at 5 hours daily costing $2.70 a month, $32.40 a year. Scale it: ten such bulbs are $27 a month, which is why whole-house LED swaps show up on bills. The per-hour cost line answers "is it worth turning off" questions directly: a 1,500-watt heater costs 27 cents per hour at 18 cents per kWh, so every hour it runs unnecessarily is a quarter tossed in the trash. Duty cycle is the only subtlety: compressors and thermostats cycle, so label wattage is the ceiling, not the average.

Worked Example

A gaming PC draws 400 watts under load, used 4 hours daily, at 18 cents per kWh. kW = 0.4. Monthly kWh = 0.4 x 4 x 30 = 48 kWh. Monthly cost = 48 x 0.18 = $8.64. Yearly = $103.68. Per hour = $0.072. Now add the 27-inch monitor at 40 watts for the same hours: 0.04 x 4 x 30 = 4.8 kWh = $0.86 a month. The setup totals under $10 a month, which surprises people who assumed gaming was expensive: the PC is a moderate load, not a heater-class load. Contrast a space heater at the same 4 hours: $32.40 a month. Heat is expensive; compute is cheap.

Reading Your Electric Bill

Bills split into supply (the energy, per kWh) and delivery (the wires, often fixed plus per-kWh). The rate to enter here is the all-in per-kWh cost: total bill divided by total kWh is the honest number, usually a few cents above the advertised supply rate. Time-of-use plans charge more during peak hours (typically late afternoon to evening) and less overnight; if you are on one, run heavy loads overnight and use the off-peak rate here. Tiered plans raise the rate past a usage threshold, which punishes the last kWh most. Know your plan type before optimizing; the wrong rate makes every calculation wrong.

Biggest Bill Cutters, Ranked

First, heating and cooling: a degree or two on the thermostat and sealed air leaks beat every gadget. Second, the water heater: 120 degrees instead of 140, plus insulation on old tanks. Third, the dryer: cold-water washing, full loads, and line drying when practical. Fourth, lighting: LEDs everywhere, payback in months. Fifth, standby loads: one smart strip per entertainment center. Sixth, the old second fridge in the garage: often 1,000+ kWh a year for convenience. Run each through the calculator before spending money; the ranking surprises almost everyone, and the surprise is the point.

Time-of-Use Rates: Shifting Load

Many utilities now charge more at peak hours (typically 4-9 PM) and less overnight; the ratio can be 2:1 or steeper. Shifting flexible loads (EV charging, laundry, dishwashing, pool pumps) to off-peak cuts those loads' cost dramatically without using less energy. The math: a 7 kWh EV charge at 35 cents peak versus 12 cents off-peak saves $1.61 per charge, or nearly $600 yearly for daily drivers. Check whether your utility offers the plan voluntarily; some enroll you by default. Smart thermostats and appliance timers automate the shifting. But beware the demand charge on some commercial-style residential plans: one 15-minute spike can set a month's fee. This calculator uses your average rate; for time-of-use precision, run major loads separately at their period rates.

Vampire Loads and the Big Hitters

Standby power ("vampire loads") draws 5-10 percent of the average home's electricity: cable boxes, game consoles, and old wall warts sip watts around the clock. A Kill A Watt meter ($25) identifies the culprits; smart power strips cut them automatically. But perspective matters: the big hitters dwarf the vampires. Ranked by typical annual cost: electric water heating, space heating/cooling, the dryer, the refrigerator, then everything else. A heat pump water heater saves more than unplugging every standby device in the house combined. Attack in order: fix the water heater and HVAC first (this calculator sizes their cost), then appliances, then the vampires. Efficiency spending follows the same ranking: insulation and heat pumps beat fancy power strips by orders of magnitude.

A Second Worked Example: The Old Garage Fridge

A 1995 garage fridge drawing an average 120 watts around the clock. Daily: 120 times 24 divided by 1,000 is 2.88 kWh. At 18 cents: 52 cents a day, $15.55 a month, about $190 a year. That fridge holds a few drinks and some bait, and it costs more per year than a modern full-size kitchen fridge. The 1995 unit has no business running; a $50 used modern fridge pays for itself in months.

Old fridges are the classic vampire because they run 24/7/365 and nobody thinks about them. The garage, the basement, the "beer fridge": each one is a line item hiding in plain sight. A plug-in meter for a week gives the true average draw, and the number usually ends the debate immediately.

Appliance Payback Math

The yearly cost figure turns shopping into arithmetic. A new $800 fridge that costs $60 a year to run versus an old one costing $190: the savings are $130 a year, so the payback is about 6 years. Longer than the fridge's likely remaining life anyway, but the math is honest. LED bulbs are the famous slam dunk: a $3 bulb saving $7 a year pays back in five months and then profits for a decade.

The formula: payback years equals price difference divided by yearly savings. Under 2 years is an obvious yes. Over 10 years is a no unless the old unit is dying anyway. In between, weigh comfort and features. And remember the calculator's yearly figure assumes today's rate; if rates rise, paybacks shorten. Efficiency is a hedge against future prices as much as a current saving.

When the Calculator Is Not Enough

Single-device math covers the big suspects, but some mysteries need whole-home data. A circuit-level energy monitor, installed in the breaker panel, shows every circuit's draw in real time: the moment the water heater kicks on, the spike when the dryer starts, the baseline hum of everything at idle. Two weeks of that data finds waste no calculator can, because you did not know the waste existed.

The usual discoveries: the "off" entertainment center drawing 60 watts, the pool pump running twice as long as needed, the dehumidifier fighting an open basement window. Monitors cost $100 to $300 plus installation, and they typically find their price in savings within the first year for curious owners. The calculator tells you what a device costs; the monitor tells you what your house actually does.