Construction GST Calculator
Add or strip GST on works-contract billing at the right rate — no more manual back-calculation.
Base value—
GST amount—
Total (incl. GST)—
sotyn.ai auto-applies the right GST on every bill type — Sales, RA, MB, T&C.
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Construction GST Calculator
Add or strip GST on works-contract billing at the right rate — no more manual back-calculation.
How to use it — and why it matters
Works-contract GST trips up billing every cycle — especially back-calculating the base value out of a GST-inclusive amount. This calculator does both directions: add GST to an exclusive amount, or strip GST out of an inclusive figure, at 18% (the common works-contract rate), 12% or 5%.
What GST rate applies to works contracts?
Most construction works contracts attract 18% GST, with 12% and 5% applying to specific categories (e.g. certain affordable housing and government works). Confirm your project's category with your tax advisor.
How do I remove GST from an inclusive amount?
Divide the inclusive amount by (1 + rate). This tool's 'Remove GST' mode does it for you and shows the base value and the GST component.
See it on your real projects
A back-of-envelope number is a start. In a free 20-minute demo we open sotyn.ai on your own trades and project sizes — no slides, no staged data.