Is the electricity cost calculator free?
Yes. It is completely free to use, with no signup, no account, and no paywall.
How accurate are the results?
The calculator uses the standard formulas for this kind of math, but real-world results can differ once fees, rounding, rate changes, and provider-specific rules come into play. Treat the output as a planning estimate, not a quote.
Does it stay local?
Yes. The numbers you enter are processed entirely in your browser and never leave your device.
Why is the monthly figure based on 30 days?
The code multiplies the daily cost by a fixed 30, which keeps the arithmetic simple and comparable across devices. It means a 31-day month is understated by about 3%, and 12 of these months come to 360 days rather than 365, so an annual estimate built from it runs about 1.4% low.
Should I use the wattage printed on the device?
Only as an upper bound. Nameplate ratings are maximums, and most appliances spend most of their time well below them. A plug-in energy meter gives you the real average draw, and that is the number worth typing in.
How do I get an annual cost?
Multiply the daily cost line by 365 yourself. Do not multiply the monthly line by 12, because that assumes a 360-day year and will read about 1.4% low.
Can it handle peak and off-peak tariffs?
No. It takes a single price per kWh. To approximate a time-of-use tariff, run the device once at the peak rate for the hours it runs during peak, then again at the off-peak rate for the remaining hours, and add the two daily costs.
Which rate on my bill should I enter?
The effective all-in rate: total bill divided by total kWh used. The headline supply rate ignores delivery and network charges, and in many markets those add 30 to 50 percent to what a kilowatt-hour really costs you.