The formula is the same for every rooftop system: kW x zone rating x deeming years, rounded down to whole certificates. Multiply the result by a price per certificate and you have an estimate of the value.
The three inputs
- System size is the rated panel capacity in kW, as installed.
- Zone rating comes from the postcode: 1.622, 1.536, 1.382 or 1.185.
- Deeming years is 5 for 2026 installs, 4 for 2027, falling by a year until 2030, when the scheme closes on 31 December.
Worked example
A 6.6 kW system in zone 3 installed in 2026: 6.6 x 1.382 x 5 = 45.6, so 45 certificates. At a market price near $38, that is about $1,710. The same system in zone 1 would produce 6.6 x 1.622 x 5 = 53.5, so 53 certificates.
| Zone | Rating | 6.6 kW, 2026 | 6.6 kW, 2027 |
|---|---|---|---|
| 1 | 1.622 | 53 | 42 |
| 2 | 1.536 | 50 | 40 |
| 3 | 1.382 | 45 | 36 |
| 4 | 1.185 | 39 | 31 |
Where people go wrong
Using the wrong install year, because the deeming years depend on when the system is installed and not when it is quoted. Using the wrong zone, which is assigned by postcode. Counting a battery here: batteries use a separate formula, covered in the battery calculator guide.
What this means for you
Use the result for a rough value, then confirm with a live rate. The pricing page shows the current Energy Merchants buy rate, and the deeming period and zone ratings guide explains the figures in depth. Related: STC trading.
Prices move, so treat any number here as a snapshot and check the live figure before you quote a job.
A calculator is a planning tool, not a guarantee. The Clean Energy Regulator confirms the final number of certificates when the claim is assessed, which is why accurate system size, postcode and installation date on the claim matter. Small data entry errors can shift the count or trigger a query.
Homeowners often use calculators to sanity check a quote. If you sell solar, expect that and be ready to show your working: the zone, the deeming years, the certificate count and the price per certificate you have assumed. Transparent numbers do more for your close rate than a vague promise of a big rebate.