GST sits on top of the valuation, never inside it
Value the work net, add ten per cent, keep the line separate. The mistake that costs money is folding GST into a rate and losing track of the taxable amount.
QScope Team · 14 May 2026 · 5 min read
Australian construction runs on GST at ten per cent. It is a simple tax, and a progress claim gets it right by keeping the valuation net and adding the tax as its own line. Trouble starts when GST leaks into the rates and nobody can say what the net value of the work actually was.
Build the claim net
Every measured rate, every variation, every retention deduction is a net figure. The progress claim adds them to a net value of work done, deducts what has already been certified and the retention, and reaches a net amount due. Only then does GST enter.
- Net value of work. Measured and variations, at contract rates, GST excluded.
- Net amount this claim. Cumulative net less previously certified less retention.
- GST. Ten per cent of the taxable amount, shown as its own line.
- Total claimed. Net plus GST, which is the figure that gets paid.
Why the payment claim needs both figures
The claim is also a payment claim under the Security of Payment Act, and it doubles as a tax invoice. The respondent certifies a net value in the payment schedule, and the GST follows the net. If the two are tangled, the schedule ends up disputing arithmetic when it meant to dispute work, and every cycle reopens a settled question.
Retention and GST
Retention comes off the net certified value, and GST is calculated after retention on the taxable amount actually being paid this cycle. When retention is later released, that release is itself a taxable supply and carries its own ten per cent. Keeping retention net throughout means the GST on release lands cleanly rather than being reverse-engineered from a gross figure.
The reconciliation test
At any point in the job you should be able to state the net value certified to date, the retention held, and the GST charged, and have them reconcile. A claim where those three cannot be separated is a claim that will cost time at the final account, when every cycle has to be unpicked to agree what the work was actually worth before tax.
One habit
Hold every rate net from the first claim. GST is the easiest number on the page when the valuation underneath it is clean, and the hardest when it is not.
QScope holds every rate and valuation net, calculates GST of ten per cent on the taxable claim, and prints the certificate and the tax invoice from the same figures.