Peak vs Off-Peak Usage Calculator
Compare a time-of-use electricity plan with peak, shoulder and off-peak rates against a flat rate, including each plan's daily supply charge.
Leave at 0 if your time-of-use plan has no shoulder period.
Your results
Cost breakdown for the billing period
| Charge | Time-of-use | Flat rate |
|---|---|---|
| Usage | $235.00 | $240.00 |
| Supply | $99.00 | $99.00 |
| Total | $334.00 | $339.00 |
Calculation breakdown
- Time-of-use cost
- (peak kWh × peak rate) + (shoulder kWh × shoulder rate) + (off-peak kWh × off-peak rate) + daily supply × days
- Flat cost
- total kWh × flat rate + daily supply × days
Worked example
Over 90 days, 300 kWh at 45c peak and 500 kWh at 20c off-peak cost $235 in usage, versus $240 on a flat 30c rate. With the same $1.10 daily supply charge on both, time-of-use is $5 cheaper; if the time-of-use supply charge were $1.20, the flat plan would be $4 cheaper.
Assumptions
- Enter rates and supply charges as shown on each plan, usually including GST.
- Your peak, shoulder and off-peak hours are set by your plan and network; check your bill or plan details.
- Excludes solar feed-in credits, discounts, demand charges and controlled-load tariffs.
How this calculator works
Enter your estimated usage split across peak, shoulder and off-peak periods along with each rate to calculate your time-of-use bill, then compare it against a flat single rate. This helps decide whether shifting usage to off-peak hours, such as running appliances overnight, would save money.
Compare time-of-use and flat electricity plans
A time-of-use plan charges different rates for peak, shoulder and off-peak periods, while a flat plan charges one rate at any time. Enter how many kilowatt-hours you used in each period, usually shown on your bill or retailer app, along with each plan's rates and daily supply charge.
The supply charge matters. In the example, time-of-use usage costs $235 against $240 on a flat plan, but a time-of-use supply charge just 10 cents a day higher over 90 days turns a $5 saving into a $4 loss.
When time-of-use pays off
Time-of-use plans usually suit households that can run dishwashers, washing machines, pool pumps or electric vehicle charging outside peak hours. If most of your use happens in the evening peak, a flat plan is often cheaper.
Peak, shoulder and off-peak hours are set by your plan and network, and they can differ between weekdays and weekends. Check your plan details, and use the government Energy Made Easy comparison site to compare offers in your area.
Official sources and assumptions
Check the official or authoritative references used to review this calculator's rates, formulas and assumptions.
Frequently asked questions
What counts as peak time?
Peak periods are set by your retailer or network, commonly weekday afternoons and evenings; check your bill or plan for exact hours.
How can I shift usage to off-peak?
Running dishwashers, washing machines, pool pumps and EV charging overnight or midday (for solar users) can reduce peak usage.
Is time-of-use always cheaper?
Only if a meaningful share of your usage happens outside peak hours; households using most power in the evening may pay more on time-of-use.
Content responsibility
Maintained by CalcAussie and last updated 3 November 2026. Checks applied: calculation method, worked examples, Australian terminology, material assumptions, official references where an external rule applies, and user-facing limitations.
Calculator results remain estimates based on the figures entered. Check material decisions against current official information and report a suspected error so it can be reproduced and corrected.
Actual prices, usage, efficiency and savings vary by provider, equipment, location and behaviour.