A valid tax invoice is what allows your GST-registered customers to claim input tax, so it must contain the details IRAS requires. For sales of S$1,000 or more (including GST), a full tax invoice should show: the words 'Tax Invoice'; your business name, address and GST registration number; an identifying invoice number; the date of issue; the customer's name and address; a description of the goods or services; and the quantity or volume.
It must also set out the GST treatment clearly – the total payable excluding GST, the GST rate and amount charged (currently 9%), and the total payable including GST. Where you make zero-rated or exempt supplies alongside standard-rated ones, show them separately.
For smaller sales of less than S$1,000 (including GST), you may issue a simplified tax invoice. This can omit the customer's details but must still show your GST registration number, the date, an invoice number, a description, and the total payable with a statement that it includes GST.
You must keep copies of the tax invoices you issue and receive for at least five years. Apexia can help you set up compliant invoice templates and GST record-keeping.