Online solar rebate calculators in Australia are all doing the same core job: estimating how many STCs a system will earn, then pricing them. Knowing what goes in helps you spot when a result looks off. If you want to do it by hand, see the step-by-step calculator method.
The four inputs
- Postcode. This sets your zone rating, from 1.185 in the coolest zone to 1.622 in the sunniest.
- System size. Panel capacity in kilowatts.
- Installation year. In 2026 the deeming period is five years. It drops to four in 2027 and ends with one year in 2030.
- STC price. The calculator assumes a figure, often around the market price. At the time of writing that has been roughly $38 to $40.
Where state programs fit
The federal STC discount is national and has no income test. States layer on top. Solar Victoria’s rebate, for example, has a household income cap that fell to $150,000 on 1 July 2026. Other states and territories run their own loans or incentives with their own conditions, and these change. A calculator that only models STCs will understate your total help in those places and overstate it if you do not qualify. Check the relevant state agency’s page.
Batteries are separate
If you are adding a battery, the Cheaper Home Batteries Program has its own STC factor, 6.8 per kWh of usable capacity for 2026 installs, stepping down to 5.7 on 1 January 2027 and 5.2 on 1 July 2027 (the factor now steps every six months to 2030). A solar-only calculator will not include it. Our battery STCs page explains the rules.
From the desk: treat any calculator result as a sense-check, not a quote. The number on your signed assignment form is what counts.
Why results differ between tools
Two calculators can give different answers for the same house. One may assume the STC price is $40, another $35. One may default to the current year and another to next year. One may include a state rebate and another may ignore it. When the results disagree, check those three settings before you assume either is wrong.
What this means for you
Use a calculator to get within a few STCs, then ask your installer to explain any gap. If the difference is large, check the zone and install year first, as those are the most common errors. The deeming period and zone ratings guide and the resources hub give you the reference tables, and how the rebate works fills in the background.