Electricity Bill Calculator: How It Works
An electricity bill is consumption multiplied by rate, plus fixed charges and taxes. Understanding the structure matters because most bills are not a flat rate — they use tiered or time-based pricing, and the same units cost different amounts depending on when and how many you use.
The unit
Electricity is billed in kilowatt-hours. One kWh is 1,000 watts drawn for one hour — a 100-watt device for ten hours, or a 2,000-watt kettle for half an hour.
kWh = (Watts × Hours) ÷ 1,000
| Appliance | Power | Daily use | kWh/month |
|---|---|---|---|
| Refrigerator | 150 W | 24 h (cycling ~⅓) | ≈ 36 |
| Air conditioner (1.5 ton) | 1,500 W | 8 h | ≈ 360 |
| Water heater | 2,000 W | 1 h | ≈ 60 |
| Washing machine | 500 W | 1 h, 4× week | ≈ 9 |
| LED lighting (10 bulbs) | 90 W | 6 h | ≈ 16 |
| Desktop computer | 200 W | 8 h | ≈ 48 |
| Ceiling fan | 70 W | 10 h | ≈ 21 |
The pattern is consistent everywhere: heating and cooling dominate. Air conditioning, water heating and electric space heating typically account for more than half a household's consumption, and lighting — the thing people switch off conscientiously — is usually a small fraction.
Tariff structures
| Type | How it works |
|---|---|
| Flat rate | One price per unit |
| Tiered / slab | Price rises as monthly consumption crosses thresholds |
| Time of use | Peak hours cost more than off-peak |
| Demand charge | Billed on your highest simultaneous draw, not just total use |
Under tiered pricing the marginal cost of the last units is much higher than the average. Cutting consumption by 10% can cut the bill by considerably more if it moves you below a threshold — so the saving is not proportional, and it is worth knowing where your thresholds sit.
The fixed portion
Bills include charges unrelated to consumption: a standing or connection charge, meter rental, distribution and network levies, and taxes. On a low-usage household these can exceed the energy cost itself, which is why halving consumption rarely halves a bill.
Standby power
Devices left plugged in draw power continuously — televisions, set-top boxes, chargers, game consoles, anything with a standby light or a clock. Individually small, collectively 5–10% of a typical household bill. Set-top boxes and game consoles in rest mode are the largest offenders by a wide margin.
Where the savings actually are
- Heating and cooling setpoints. One degree typically changes consumption by 5–10%, which is the single largest controllable lever.
- Water heating. Lowering the thermostat and insulating the tank.
- Shifting load off-peak where time-of-use pricing applies.
- Replacing an old refrigerator, which runs continuously and may use several times what a modern one does.
- Lighting — worthwhile but a small share of the total.
Estimates here depend entirely on the wattage and hours you enter. For real figures, use a plug-in meter on individual appliances, or your utility's own consumption data if a smart meter is installed.