What this calculator does
An electricity bill calculator works out what a power bill should come to before it arrives, from three numbers most bills are actually built from: how much electricity was used, the price charged per unit, and a fixed daily charge for simply being connected to the grid. Multiply usage by the rate, add the supply charge for every day in the billing period, and that total is the bill.
The reason this needs a calculator rather than a rule of thumb is that electricity pricing is never one flat number. Rates and supply charges differ by provider, by state or region, by whether a plan has time-of-use pricing, and they change over time as contracts are renewed. Every rate here is a field you fill in from your own bill or plan, not a number baked into the tool, so the result stays accurate as pricing changes.
The formula
Usage cost is the electricity used, in kilowatt-hours (kWh), multiplied by the rate charged per kWh. The supply charge, a fixed daily fee for being connected regardless of usage, is multiplied by the number of days in the billing period. Adding the two gives the total bill.
| Term | Meaning |
|---|---|
| kWh (kilowatt-hour) | The standard unit electricity is billed in: one kilowatt of power used for one hour. |
| Rate per kWh | The price charged for each kilowatt-hour used, set by the electricity provider or plan. |
| Supply charge | A fixed daily fee charged just for being connected to the electricity network, independent of how much power is used. |
| Billing period | The number of days the bill covers, typically around 30, 60 or 90 days depending on the provider. |
The inputs explained
| Field | What to enter |
|---|---|
| Electricity used (kWh) | Total electricity used over the billing period, in kilowatt-hours, as shown on a bill or meter reading. |
| Rate per kWh ($) | The price per kWh from your electricity plan. This varies by provider and region, so check a recent bill for the actual figure. |
| Daily supply charge ($) | The fixed daily supply or service charge from the same plan, billed regardless of usage. |
| Billing period (days) | The number of days the bill covers. |
When to use it
Checking a bill before paying it
Reading the kWh used, the rate and the supply charge straight off a bill and recalculating the total is a direct check that the arithmetic on the bill itself is correct.
Comparing two electricity plans
Running the same usage figure through two different rate and supply-charge combinations shows which plan actually costs less for a household's real usage pattern, rather than relying on an advertised headline rate alone.
Estimating a bill before it arrives
A meter reading partway through a billing period, projected out at the plan's rate and supply charge, gives an early estimate of what the full bill will come to.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does the bill change with electricity used, at a fixed rate and supply charge?
A 90-day billing period at a fixed rate and supply charge, across a range of usage levels.
| Electricity used | Estimated bill | Usage cost | Effective cost per kWh (incl. supply charge) |
|---|---|---|---|
| 300 kWh | $189.00 | $90.00 | $0.63 |
| 600 kWh | $279.00 | $180.00 | $0.47 |
| 900 kWh | $369.00 | $270.00 | $0.41 |
| 1,200 kWh | $459.00 | $360.00 | $0.38 |
| 1,500 kWh | $549.00 | $450.00 | $0.37 |
| 2,000 kWh | $699.00 | $600.00 | $0.35 |
How does the bill change with the rate per kWh, at a fixed usage and supply charge?
A fixed 900 kWh of usage over 90 days, across a range of rates per kWh.
| Rate per kWh | Estimated bill | Usage cost |
|---|---|---|
| $0.20 | $279.00 | $180.00 |
| $0.25 | $324.00 | $225.00 |
| $0.30 | $369.00 | $270.00 |
| $0.35 | $414.00 | $315.00 |
| $0.40 | $459.00 | $360.00 |
| $0.45 | $504.00 | $405.00 |
Questions
Why does my bill still charge something even in a month I barely used any power?
The daily supply charge is billed regardless of usage, since it covers the cost of being connected to the network rather than the electricity itself. A near-zero usage month still carries the full supply charge for every day of the billing period.
Does this account for time-of-use or tiered pricing?
No. This calculator uses one flat rate per kWh across the whole billing period. Plans with time-of-use pricing (different rates for peak, off-peak and shoulder periods) or tiered pricing (a different rate above a usage threshold) need each rate applied to its own usage separately and the results added together.
Where do I find my rate and supply charge?
Both are printed on an electricity bill, usually alongside the usage figures, or listed in the plan's pricing fact sheet from the retailer. They vary by provider, region and plan, which is why they are entered here rather than assumed.
Why is my effective cost per kWh higher than the advertised rate?
The advertised rate is usually just the usage rate, without the daily supply charge folded in. Once the supply charge is spread across the actual kWh used, the effective cost per unit is always somewhat higher, and more noticeably so for low-usage households.
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