Electricity Cost

Features

• Energy from power × hours: 1 unit of electricity is 1 kWh, power divided by 1000 first
• ⚠️ Tiered tariffs band the total rather than charging the top rate on everything
• ⚠️ Standby draw is 24 hours a day, unrelated to hours of use
• Energy and cost given per day, per month and per year
• Presets for common devices (air conditioner, heater, fridge, washing machine, computer…), or type your own power
• The tariff comes from your bill — no invented “standard rate”
• Standby can be toggled, with an “equals running the device for” conversion
• Everything runs locally, with no network requests

How to use

1. Pick a device preset, or leave it on custom and type the power in watts
2. Enter the hours used per day and the billing period (30 days by default)
3. Enter your tariff; for a tiered tariff, switch it on and fill in the two limits and three rates
4. To include standby, switch it on and enter the standby power in watts
5. The energy and cost appear per day, per month and per year

FAQ

Is one unit of electricity 1 kW or 1 kWh?

It is 1 kWh (a kilowatt-hour). kW is power; kWh is power times time. A 1000 W appliance for one hour uses 1 kWh; a 100 W bulb for ten hours also uses 1 kWh. Energy is therefore “power ÷ 1000 × hours”, not “power”. The formula is printed beside the result here so that step stays visible.

How does a tiered tariff work?

The total is split across bands, each billed at its own rate. With the first 200 kWh at 0.50 and the next band at 0.55, using 300 kWh means 200 kWh at 0.50 plus 100 kWh at 0.55 — 155 in total. The usual mistake is `300 × 0.55 = 165`, charging the top rate on the cheap band too. The per-band rows here list each band’s energy and cost so they can be checked one by one.

Does standby really use much?

It depends on the device. A router idles at roughly 5–15 W, which is 44–131 kWh a year if never switched off; set-top boxes and older TVs are worse. One device is little, but a house full of always-on devices easily adds up to tens or hundreds of kWh a year. The defining feature is that it is unrelated to whether you are using the device — hence the 24-hour basis. Counting it is what tells you which devices deserve a switched socket.