You must register for GST if your taxable turnover is:
Under the retrospective view, more than $1 million at the end of the calendar year, or
Under the prospective view, expected to be more than $1 million in the next 12 months
If you are not liable for GST registration, you may choose to register voluntarily after careful consideration.
You may also be liable for GST registration under the Reverse charge and Overseas vendor registration regime. For more information, please refer to the section on Reverse charge and overseas vendor registration below.
Source: gov.sg
