Worked Examples and Comparison Checklists
Flat rate vs time-of-use: a worked example to see which costs you less
Compare a flat electricity rate with time-of-use and free-midday plans using your own load profile — three household examples with the arithmetic and a break-even test.
A time-of-use plan is cheaper than a flat rate only if enough of your electricity is used outside the peak period to make up for the higher peak price. The quick test is to work out your blended rate — the weighted average of the peak, shoulder and off-peak rates using your own percentages — and add the difference in supply charges. If the blended rate plus supply is lower than the flat-rate plan's cost for the same usage, time-of-use wins. This guide shows the test for three different households, a break-even calculation for peak share, and how a free midday window changes the answer.
What you need
- 12 months of interval data, or at least one bill per season showing peak, shoulder and off-peak kWh (if you are already on time-of-use)
- The rates, period times and supply charge for each plan you are comparing (from Energy Made Easy or Victorian Energy Compare)
- If you are on a flat rate now, a smart meter data download from your retailer or distributor to see when you use power
The concepts are explained in the time-of-use and demand tariff guide.
The plans in the example
Illustrative plans only, not real offers:
| Plan | Supply | Peak | Shoulder | Off-peak | Free midday |
|---|---|---|---|---|---|
| Flat | 110 c/day | 32 c (all times) | — | — | — |
| Time-of-use (ToU) | 110 c/day | 46 c | 30 c | 22 c | — |
| Free-midday ToU | 120 c/day | 48 c | 30 c | 24 c | 0 c for 3 hours |
All households use 6,000 kWh a year. Supply charges per year: flat and ToU $401.50; free-midday $438.
Household A: working couple, evening-heavy use
Usage split: 50% peak, 25% shoulder, 25% off-peak; 5% of total is in the midday window (counted within shoulder above).
- Flat: 6,000 × $0.32 = $1,920 + $401.50 = $2,321.50
- ToU: 3,000 × $0.46 + 1,500 × $0.30 + 1,500 × $0.22 = $1,380 + $450 + $330 = $2,160 + $401.50 = $2,561.50
- Free-midday: 300 kWh free; peak 3,000 × $0.48 = $1,440; shoulder 1,200 × $0.30 = $360; off-peak 1,500 × $0.24 = $360; = $2,160 + $438 = $2,598
Result: the flat rate is cheapest by about $240. Household A should stay on a flat rate unless it can move use away from the evening.
Household B: family at home, flexible appliances
Usage split: 30% peak, 35% shoulder, 35% off-peak; with a free window, 25% of total (1,500 kWh) can be moved there from shoulder and peak.
- Flat: $2,321.50
- ToU: 1,800 × $0.46 + 2,100 × $0.30 + 2,100 × $0.22 = $828 + $630 + $462 = $1,920 + $401.50 = $2,321.50
- Free-midday: free 1,500 kWh; peak 1,200 × $0.48 = $576; shoulder 1,200 × $0.30 = $360; off-peak 2,100 × $0.24 = $504; = $1,440 + $438 = $1,878
Result: ToU and flat are equal at this split; the free-midday plan saves about $443 a year because the household moves laundry, dishwasher, pool pump and hot water timer into the free window. (In this example the 1,500 kWh moved came from 600 kWh of peak and 900 kWh of shoulder.)
Household C: EV owner charging overnight
Usage split: 20% peak, 20% shoulder, 60% off-peak (EV charging overnight).
- Flat: $2,321.50
- ToU: 1,200 × $0.46 + 1,200 × $0.30 + 3,600 × $0.22 = $552 + $360 + $792 = $1,704 + $401.50 = $2,105.50
- Free-midday (charging moved to midday only on days at home, say 1,200 kWh): peak 1,200 × $0.48 = $576; shoulder 1,200 × $0.30 = $360; off-peak 2,400 × $0.24 = $576; = $1,512 + $438 = $1,950
Result: ToU saves about $216 over flat; free-midday saves another $155 if the car is often home at midday.
The break-even peak share
For the ToU plan above versus flat (same supply charge), assume shoulder and off-peak are split evenly in the non-peak share. The non-peak average is (30 + 22) ÷ 2 = 26 c. ToU equals flat when:
peak share × 46 + (1 − peak share) × 26 = 32 → peak share × 20 = 6 → peak share = 30%
So with these illustrative rates, if more than about 30% of your use falls in the peak period, the flat rate is likely cheaper. Repeat this with your actual rates; the break-even point changes with every plan.
Summary
| Household | Flat | ToU | Free-midday | Cheapest |
|---|---|---|---|---|
| A (evening-heavy) | $2,321.50 | $2,561.50 | $2,598 | Flat |
| B (flexible) | $2,321.50 | $2,321.50 | $1,878 | Free-midday |
| C (EV overnight) | $2,321.50 | $2,105.50 | $1,950 | Free-midday if home at midday, otherwise ToU |
The free-midday plan here is styled on the Solar Sharer Offer and Victoria's Midday Power Saver; real prices are regulated and differ by zone. Check the Solar Sharer and Midday Power Saver guide.
How to run this for your home
- Download your interval data and add up kWh by period for a full year (or a summer and a winter quarter).
- Price each plan with the formula: supply × days + Σ(kWh in period × rate).
- Ask honestly how much you can move: timers on the dishwasher and hot water are easy; cooking dinner at midday is not.
- Check a quarter with the quarterly bill estimator using your blended rate.
- Confirm on the comparison sites, as in the step-by-step comparison.
If you have solar, add your exports and feed-in tariff, as shown in the solar exports worked example.
FAQ
Does a smart meter force me onto time-of-use?
Not necessarily. Your retailer may still offer flat-rate retail plans even if the network tariff is time-of-use. Ask, and compare both.
What if my usage changes between summer and winter?
Run the test for both seasons. Air conditioning in summer evenings or heating in winter evenings can push your peak share above break-even.
Is a demand tariff the same as time-of-use?
No. A demand tariff adds a charge based on your highest kW in a window; time-of-use only varies the per-kWh rate. Demand plans need a separate calculation.
Sources
- Energy Made Easy — compare flat and time-of-use plans with your data
- Victorian Energy Compare — upload Victorian smart meter data
- Australian Energy Regulator — time-of-use DMO and Solar Sharer pricing
- Essential Services Commission — VDO time-of-use and Midday Power Saver
