Most people guess wrong about what drives their electricity bill. The phone charger gets unplugged religiously while the pool pump runs eight hours a day unquestioned. The good news: you do not need to guess, because running costs follow one small formula, and once you can run it, every appliance in the house becomes an open book.
The only formula you need
kilowatts × hours used × your usage rate = cost.
Take the appliance's power in kilowatts (kW), multiply by the hours it runs, then multiply by your usage rate per kWh from your bill. That is the whole trick.
Three worked examples at a rate of 30 cents per kWh:
- A 2,400 watt (2.4 kW) fan heater running 4 hours: 2.4 × 4 × $0.30 = $2.88 a night, or roughly $86 a month if it happens every evening.
- A 1,000 watt (1 kW) pool pump running 8 hours: 1 × 8 × $0.30 = $2.40 a day, over $870 a year.
- A 10 watt LED bulb for 5 hours: 0.01 × 5 × $0.30 = 1.5 cents. Leave the crusade against light bulbs to history.
Wattage is on a label or plate on the appliance itself, in the manual, or a quick search away. Two catches: heating and cooling appliances cycle on and off, so real usage is often below the plate rating, and appliances with compressors or elements (fridges, air conditioners, dryers) vary with settings and weather. Treat the formula as a strong estimate, not an invoice.
The loads that actually matter
Applying that formula across a typical home, a consistent hierarchy appears:
- Heating and cooling. The biggest swing factor in most Australian homes. Anything that changes air temperature moves kilowatts, and it runs for hours. This is why bills jump in heatwaves and cold snaps, and why a one-degree thermostat adjustment does more than a drawer full of chargers.
- Hot water. If your water is heated electrically, it is usually the biggest single appliance in the house. It often sits on its own cheaper tariff; our controlled load guide explains that second line on your bill.
- Pool pumps and spas. Modest wattage, brutal hours. A pump timer and a shorter run in winter are among the cheapest wins in any house that has one.
- The laundry, driven by heat. A dryer is an electric heater with a drum. Washing in cold water and line drying attack the heat, which is where the money is.
- The kitchen. Ovens and cooktops draw plenty but run briefly. The fridge draws little but never stops, so an old inefficient second fridge in the garage can quietly cost more than the new one in the kitchen.
- Standby and gadgets. Real, but small. Chasing standby power is worth doing once (smart power boards, switching off the rarely-used TV), then moving on to the loads above.
Turning this into a smaller bill
Two levers, and you control both. The first is usage: fewer kilowatt-hours through the big loads above. The second is price: paying less for every kilowatt-hour you do use, which is usually the faster win because it takes ten minutes and no lifestyle change.
Your bill gives you the two numbers that matter: your average daily usage in kWh and your usage rate (our bill reading guide shows where). Put them into our free calculator and it prices your current plan against every retailer you add, per day, month and year. Pick your State; in Queensland, New South Wales, Victoria, South Australia, Tasmania and the ACT you can import real plans for your postcode from government data.
If the bill is high and you want to know whether the house or the plan is to blame, our high bill checklist walks the full diagnosis. And if you find the culprit is a big shiftable load like the pool pump or dishwasher, a tariff that rewards off-peak running may suit you; see our time-of-use guide before you switch shapes.