Searches for “STC deeming 2026”, “2027” and so on all point at the same table. Here it is, followed by what the numbers do.
The deeming period by year
| Installation year | Deeming period (years) |
|---|---|
| 2025 | 6 |
| 2026 | 5 |
| 2027 | 4 |
| 2028 | 3 |
| 2029 | 2 |
| 2030 | 1 |
| 2031 onwards | Scheme ended 31 December 2030 |
This applies to small-scale rooftop solar. One extension: systems above 100 kW and up to 1 MW installed from 1 October 2026 can create STCs with a fixed five-year deeming period. See mid-scale solar STCs if that is your project.
STC deeming 2026
Five years. A system installed anywhere in Australia between 1 January and 31 December 2026 uses 5 as its deeming period. Because the deeming period is a multiplier, the 2026 number is the most generous one left in the scheme.
STC deeming 2027, 2028, 2029 and 2030
Each year the multiplier drops by one: 4 in 2027, 3 in 2028, 2 in 2029 and 1 in 2030. See how much STCs fall in each of those years for the dollar effect, and what changes in January 2027.
The formula in one line
STCs = system size in kW x zone rating x deeming period, rounded down to a whole number.
Zone ratings come from your postcode: zone 1 is 1.622, zone 2 is 1.536, zone 3 is 1.382 and zone 4 is 1.185. Sydney, Brisbane, Perth, Adelaide, Canberra, the Gold Coast, Newcastle, Wollongong, Cairns and Townsville are zone 3. Melbourne, Geelong, Hobart and Launceston are zone 4. Darwin is zone 2 and Alice Springs is zone 1.
Worked example
A 6.6 kW system in Sydney (zone 3), installed in 2026: 6.6 x 1.382 x 5 = 45.6, rounded down to 45 STCs. The same system in 2027 gives 6.6 x 1.382 x 4 = 36.5, or 36 STCs. At roughly $38 to $40 per STC at the time of writing, that is a difference of about $350 on the discount.
What this means for you
Use the STC calculator to enter your postcode and size, and see your own number rather than the example. The deeming period and zone ratings resource goes into the zone maps. If you are an installer, pricing has today’s rate and how it works explains settlement.