Electric bills feel like weather — discussed constantly, understood rarely. The truth is that bill math is three multipliers long, and once you can do it, the villains of your bill identify themselves in about twenty minutes.
The whole formula
Yearly cost = watts ÷ 1,000 × hours/day × 365 × your rate
A 1,500W space heater, 3 hours a day, at 16¢/kWh: 1.5 × 3 × 365 × $0.16 ≈ $263/year. A 10W always-on router: 0.01 × 24 × 365 × $0.16 ≈ $14. The electricity cost calculator runs this for anything with a nameplate.
Duty cycles: the honest watts
Nameplate wattage is peak draw, and appliances with thermostats don't run at peak all day. Fridges cycle: a "1,200W" compressor averages 100–200W across 24 hours. Water heaters draw hard for an hour then coast. Space heaters and incandescent-equivalent heat are the honest ones — they draw nameplate the entire time they run, which is exactly why they dominate bills. When precision matters (that garage fridge you suspect), a $15 plug-in power meter ends the argument in a day.
Finding your effective rate
Take the bill's total ÷ total kWh delivered. The headline "12¢/kWh" on the marketing page excludes delivery charges, riders, and taxes that routinely double the real number. Using the effective rate is the difference between estimating your bill and underestimating it by half.
The usual suspects, ranked
- Electric heating of any kind — space heaters, dryers, water heaters, legacy baseboard — is the bill's heavyweight division.
- Cooling runs second in summer states, moderated heavily by the thermostat setting you can actually tolerate.
- The garage fridge is the classic $15–25/month fossil; decommission it before buying a single smart plug.
- Lighting and electronics are mostly rounding errors post-LED — audit them last, if ever.
Twenty minutes of calculator math against your last twelve bills tells you more than any gadget — and points the efficiency money at the appliances that actually eat.