A business must register for GST when it becomes liable under either of IRAS’s compulsory registration tests:
- Retrospective test: taxable turnover exceeds S$1 million for the calendar year. The business generally applies between 1 and 30 January of the following year, with GST registration taking effect from 1 March.
- Prospective test: at any time, there are reasonable grounds to expect taxable turnover to exceed S$1 million in the next 12 months. The business must generally apply within 30 days of the forecast date. For liabilities arising on or after 1 July 2025, registration generally takes effect two months from that forecast date.
Businesses below the compulsory threshold may apply for voluntary GST registration if they meet IRAS’s conditions. Whether turnover is “taxable turnover” depends on the GST treatment of the supplies, not simply gross accounting revenue.