OneTaskBy Tim King · Updated
Utility Bill Calculator
Electricity, Gas and Water Bills From Meter Readings and kWh Rates
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How the Utility Bill Calculator works
This utility bill calculator estimates an electricity, gas or water bill before it arrives. Enter two meter readings or the units used, the unit rate and the daily supply charge from your plan, and any discount and tax rate shown on your bill. It returns the total, the usage and supply charges and the average cost per day.
Utility bill calculator formula
Most electricity, gas and water bills have two parts: a usage charge for each unit used (kWh, megajoule, litre or kilolitre) and a fixed supply charge for each day of the billing period. Any discount comes off next, and then tax is added at the rate on your bill:
Usage charge = units × unit rate ÷ 100 Supply charge = days × daily supply charge ÷ 100 Total = (usage + supply − discount) × (1 + tax rate ÷ 100)
Rates are entered in cents because that is how most plans quote them. The utility bill calculator does not hold any rates or tax rates; enter the ones on your own plan and bill.
Worked example: a quarterly electricity bill
The meter went from 1,000 to 1,650, so 650 kWh were used over 91 days. At 30 cents a kWh the usage charge is 195.00, and a supply charge of 110 cents a day adds 100.10. A 10% discount takes off 29.51, leaving 265.59, and 10% tax adds 26.56 for a total of 292.15, or 3.21 a day.
Worked example: checking a cheaper plan
The same 650 kWh on a plan at 27 cents a kWh with a 130-cent supply charge and no discount comes to 175.50 + 118.30 = 293.80 before tax, more than the first plan after its discount. A lower unit rate does not always mean a lower bill when the supply charge is higher.
Utility bill reference table
Bills over 91 days at 30 cents a unit and a 100-cent daily supply charge, before discount and tax.
| Units a day | Units in 91 days | Usage charge | Supply charge | Bill |
|---|---|---|---|---|
| 2 | 182 | 54.60 | 91.00 | 145.60 |
| 4 | 364 | 109.20 | 91.00 | 200.20 |
| 6 | 546 | 163.80 | 91.00 | 254.80 |
| 8 | 728 | 218.40 | 91.00 | 309.40 |
| 10 | 910 | 273.00 | 91.00 | 364.00 |
| 12 | 1,092 | 327.60 | 91.00 | 418.60 |
| 14 | 1,274 | 382.20 | 91.00 | 473.20 |
| 16 | 1,456 | 436.80 | 91.00 | 527.80 |
| 18 | 1,638 | 491.40 | 91.00 | 582.40 |
| 20 | 1,820 | 546.00 | 91.00 | 637.00 |
| 22 | 2,002 | 600.60 | 91.00 | 691.60 |
| 24 | 2,184 | 655.20 | 91.00 | 746.20 |
| 26 | 2,366 | 709.80 | 91.00 | 800.80 |
| 28 | 2,548 | 764.40 | 91.00 | 855.40 |
| 30 | 2,730 | 819.00 | 91.00 | 910.00 |
| 32 | 2,912 | 873.60 | 91.00 | 964.60 |
| 34 | 3,094 | 928.20 | 91.00 | 1,019.20 |
| 36 | 3,276 | 982.80 | 91.00 | 1,073.80 |
| 38 | 3,458 | 1,037.40 | 91.00 | 1,128.40 |
| 40 | 3,640 | 1,092.00 | 91.00 | 1,183.00 |
Quick answers
- 500 kWh at 30 cents is 150.00 in usage.
- A 100-cent supply charge over 91 days is 91.00.
- 10 kWh a day at 30 cents is 3.00 a day in usage.
- A 1,500 W heater run for 4 hours uses 6 kWh.
- The supply charge is paid even when usage is zero.
- Subtract the previous reading from the current one to see how many units you used: 1,650 minus 1,000 is 650.
FAQ
How do I read my meter?
Read the numbers left to right, ignoring any digits after a decimal point or in a red box. Subtract the reading on your last bill from today's reading to get the units used since then.
What is a supply charge?
It is a fixed daily charge for being connected to the network, paid whatever you use. On low-usage homes it can be a large share of the bill.
Why is my estimate different from the bill?
Bills can include tiered or time-of-use rates, solar feed-in credits, concession rebates and rounding. This calculator uses a single unit rate, so split the usage into separate runs if your plan charges peak and off-peak differently.
See also: all Bills tools, Pay, Property, Debt, Investing, Saving.
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