GST on STCs

Home systems: no GST on the assignment

The ATO's position is that a homeowner who is not carrying on a business, and is not registered or required to be registered for GST, does not make a taxable supply when they assign the right to create STCs.

For the trader or agent, that has a direct cost: it cannot claim a GST credit on what it pays for that right. For the retailer or installer, it means the trader's payment is not grossed up with GST and there is no separate GST to remit on it.

The customer's invoice

Your GST on the sale is worked out on the full price of the system, before the STC discount, not on the amount the customer ends up paying. The ATO gives this kind of example, where the homeowner assigns the right to a separate agent:

That $400 is more than 10% of the $3,800 the customer paid. That is expected, and the ATO says so.

Business systems: GST applies

When the owner is registered or required to be registered for GST and the system is used in their business, the assignment is a taxable supply by the owner. The GST is based on the sale price, delayed cash payment or upfront discount.

• The owner issues a tax invoice to the buyer if the amount is more than $82.50 including GST.
• The invoice comes from the system owner, because the owner is the one assigning the right, even if the money goes to the retailer as part of the discount.
• The buyer can then claim a GST credit, if it is registered or required to be.
• The owner's own GST credit on buying the system is based on the price before the discount, less any personal use.

Selling or transferring certificates

Creating or registering an STC in the REC Registry carries no GST. Selling or transferring one does, if you are registered or required to be registered for GST. That applies to agents and traders selling on, and the regulator's clearing house price of $40 is before that GST.

Keep your GST details current in the REC Registry. The regulator says it cannot adjust a completed transaction if GST was applied incorrectly.

Comparing trader prices

Ask each trader two questions: what lands in my account per STC on a home system, and what on a system owned by a GST-registered business? Those two answers can be compared directly, whatever the headline number says.

Here is our answer, as at 3 November 2026:

This page summarises the ATO's public guidance. It is not tax advice. Your accountant can confirm how it applies to your business, and you can ask the ATO directly.