The deeming period is the number of years of expected output the scheme pays for upfront. For small-scale solar it is the single biggest driver of the rebate, and it falls by one year every 1 January until the scheme ends on 31 December 2030. For a 6.6 kW system in Sydney, that means 45 STCs now, 36 next year, 27 the year after, and so on.
This guide lays out the whole schedule for 2026 to 2030, by zone, in dollars, and covers what does not follow this pattern: batteries and mid-scale solar.
The rule
Certificates for a small solar system are kW x zone rating x deeming years, rounded down. The deeming years equal the number of years left in the scheme, counting the install year:
| Install year | Deeming years |
|---|---|
| 2026 | 5 |
| 2027 | 4 |
| 2028 | 3 |
| 2029 | 2 |
| 2030 | 1 |
Zone ratings are 1.622 for zone 1, 1.536 for zone 2, 1.382 for zone 3 and 1.185 for zone 4. Zone 3 covers Sydney, Brisbane, Perth, Adelaide, Canberra, the Gold Coast, Newcastle, Wollongong, Cairns and Townsville. Zone 4 covers Melbourne, Geelong, Hobart and Launceston. Darwin is zone 2 and Alice Springs zone 1. Confirm any individual postcode in the CER’s table. See zone ratings for how to look one up.
STCs for a 6.6 kW system, 2026 to 2030
| Zone | 2026 | 2027 | 2028 | 2029 | 2030 |
|---|---|---|---|---|---|
| 1 (1.622) | 53 | 42 | 32 | 21 | 10 |
| 2 (1.536) | 50 | 40 | 30 | 20 | 10 |
| 3 (1.382) | 45 | 36 | 27 | 18 | 9 |
| 4 (1.185) | 39 | 31 | 23 | 15 | 7 |
In dollars for zone 3 at an illustrative $38 per STC: $1,710, $1,368, $1,026, $684 and $342. The drop each January is $342 on this system, a constant slice because the deeming loses one year and the zone rating is fixed.
For a 10 kW system in zone 4: 59, 47, 35, 23 and 11 STCs across the five years, or about $2,242 falling to $418 at $38. In relative terms the cut gets steeper: 20% from 2026 to 2027, then 25%, 33% and 50%.
What it means for selling
Customers. The discount on the quote shrinks every January, which gives a real reason to install before the year turns, though it is a smaller reason than it sounds. On a 6.6 kW system, $342 is about 4% of a typical net price. See should you buy solar before 2027.
Installers. The shrinking discount makes pricing more visible. A customer who sees $1,710 off in 2026 and $1,368 in 2027 will notice. Sales teams that explain the rule, with the date it applies from, avoid disputes. The STC calculator shows the effect by postcode.
Cash flow. A larger share of income each year comes from the sale price of the system, and a smaller share from certificates. That changes the margin conversation and the importance of fast settlement. See installer cash flow.
The date that counts
The installation date determines the deeming year, not the quote, deposit or contract date. If the install date is 31 December 2026, you get five years. If it is 2 January 2027, you get four. A job in the pipeline at year end needs a written install date and a note of what happens if it slips. See what changes in January for the planning checklist.
What does not follow the deeming rule
Batteries. Battery certificates use usable kWh, three tiers (100% on the first 14 kWh, 60% to 28, 15% to 50) and a factor that steps down every six months: 6.8 at the time of writing, 5.7 from 1 January 2027, 5.2 from 1 July 2027, and lower to 2030. A 13.5 kWh battery creates 91 STCs now, 76 in the first half of 2027 and 70 in the second. See the tier explainer.
Mid-scale solar. Systems above 100 kW and up to 1 MW installed from 1 October 2026 have a fixed five-year deeming period, per the 2026 amendment to the Renewable Energy (Electricity) Regulations. The CER says applications open mid to late November 2026. A 250 kW zone 3 system creates 1,727 STCs under that rule, about $65,600 at $38. The pillar page is mid-scale solar STCs. Above 1 MW, systems remain in the large-scale scheme and create LGCs.
Heat pumps and solar water heaters. The count depends on the registered model and zone and uses a deeming period that also shortens. Check the CER’s figures for the model on the day.
Why 2030
The Renewable Energy Target legislation runs to 2030, and the small-scale scheme ends on 31 December 2030. That is the reason the deeming period steps down by one a year. After 2030, no new certificates are created for small-scale systems. See what happens when the scheme ends and the 2026 deeming answer.
A planning table for a sales team
- Set the install date first. Quote the STC discount for the date the job will be installed.
- Flag December jobs. Track any job within three weeks of 31 December.
- Put the rule in the contract. “The STC discount is calculated at the deeming period applying on the installation date.”
- Review each October. Re-run margins for the next year’s count.
- Watch mid-scale. If you quote commercial roofs, run both a 99 kW and a 250 kW option.
Questions that come up every December
A job was sold in 2026 but installed in 2027. Which deeming period applies? The installation date decides, so the 2027 period of four years applies. Say so in the contract.
Does the date of the electrical compliance certificate matter? The installation date is determined by the rules on electrical safety in your state, and it needs to be consistent across the claim, the certificate and the invoice. If they differ, ask your trader before lodging.
Do additions get their own period? Panels added to an existing system are a new installation with their own date and count, at the deeming period in force when the additions are completed.
Can we speed up a job to beat 1 January? Yes, but only if the work is finished to standard. A rushed job that fails inspection is a worse outcome than losing $342 on a 6.6 kW system. See the deeming period schedule by year for a quick reference.
What about a customer who delays? Offer a written choice: install by a date, or accept the lower discount. It keeps the decision with the customer and keeps your margin intact.
What to do next
- Use the STC calculator on three recent quotes and re-run them at the 2027 deeming period.
- Add the date rule to your quote template.
- Read the scheme guide for installers for the rest of the picture.
- For rates, see pricing, and start trading when you are ready to lodge.