Every tool here prints its formula next to the result, uses the rate you type in rather than a guessed local tariff, and keeps fixed charges separate from usage. If a result looks wrong, you can check the arithmetic on paper. Nothing you enter is sent anywhere.
There are two tools, and they answer different questions:
- Two-bill comparison: why did the bill change? Enter the kWh, days and total from two bills. It works out kWh per day and labels the change as a price, billing-period or usage change.
- Electricity cost calculator: what does one appliance cost? Use watts mode with the label wattage and hours per day, or meter mode with the kWh a plug-in meter recorded and the days it covered. Type your rate in cents or dollars.
Pick by the question you have. If you do not know yet whether usage went up, compare the bills first; pricing an appliance only helps once kWh per day has risen. For anything with a thermostat or compressor, such as a fridge, freezer or dehumidifier, a few days of meter readings beat the label. The plug-in monitor guide covers which meter fits which job.
Both tools give flat-rate estimates. Tiered and time-of-use tariffs are not modeled, and neither covers gas, oil or propane.