Multiply the units you used by the rate, add the fixed charge and any duty, and you have the bill: 250 units at 8 plus a fixed 100 is 2,100. Enter your units or two meter readings and your own flat or slab rates.
The formula
Units from readings
units = current reading − previous readingEnergy charge, flat rate
energy = units × rate per unitEnergy charge, slabs
energy = sum of (units in each slab × that slab's rate)The bill
bill = energy + fixed charge + (energy + fixed charge) × duty ÷ 100The rates are yours: take them from your own tariff or bill. Each slab's charge is rounded to the cent, so the table always adds up to the energy charge.
Worked example
On one flat rate of 8, 250 units and a fixed charge of 100 come to 2,100, an average of 8.40 a unit.
When to use it, and the mistakes to avoid
Use it to check a bill before you pay it, to estimate next month's from the units you expect to use, or to see what a change in use or in rates would cost.
- Charging all units at the top rate. In a slab tariff each slab has its own rate.
- Reading the meter the wrong way round. Current minus previous, not the other way.
- Leaving out the fixed charge. Include any meter rent or fixed monthly charge.
- Using last year's rates. Tariffs change, so use the latest.
- Forgetting duty or tax. Add the percentage if your bill carries it.
FAQ
How do I calculate an electricity bill?
Multiply the units you used by the rate per unit, add the fixed charge, and add any duty or tax. 250 units at 8 is 2,000, and a fixed charge of 100 makes 2,100. If your tariff has slabs, each block of units is charged at its own rate and the results are added together.
What is a unit of electricity?
One unit is one kilowatt-hour (kWh): the energy a 1,000 watt appliance uses in an hour. A 100 watt bulb left on for 10 hours uses 1 unit. Your bill states the units for the billing period, and your meter counts them.
How do I get the units from meter readings?
Subtract the previous reading from the current one. If last month's reading was 12,345 and this month's is 12,612, you used 267 units. Choose 'The two meter readings' and enter both. If the meter has gone past its top digit and started again from zero, add the units up to that point yourself and enter the total as units used.
How do slab rates work?
The rate rises in steps as use rises, and each step applies only to the units inside it, not to all of them. With the first 100 units at 3.50, the next 100 at 5, the next 100 at 7 and the rest at 9.50, a use of 350 units costs 350 + 500 + 700 + 475 = 2,025 in energy charge. The table under the result shows each slab.
Where do I find my rates?
On your last bill, or in the tariff your supplier or electricity board publishes for your area and type of connection. Rates differ by state, supplier, consumer category (home, shop, farm) and date, and they change, so this calculator does not carry any. It works with the ones you type in.