A GST invoice is the primary document that records a supply of goods or services and forms the legal basis for charging tax and claiming input tax credit (ITC). Getting the format, fields and timing right is not merely good practice \u2014 it is a statutory requirement under the CGST Act, 2017. This guide explains what a tax invoice is, the mandatory particulars, the different invoice-type documents, the time limits for issue and the rules on invoice numbering, as applicable in 2026.<\/p>\n
Under Section 31 of the CGST Act, a registered person supplying taxable goods or services must issue a tax invoice showing the description, quantity and value of the supply, the tax charged and other prescribed particulars. The tax invoice serves three core purposes: it evidences the supply, it is the document on which GST is charged and collected, and it enables the recipient to claim ITC. Without a valid tax invoice that meets the prescribed conditions, a buyer generally cannot claim credit of the tax paid.<\/p>\n
A tax invoice is issued only for taxable supplies. Where a supply is exempt, or the supplier is registered under the composition scheme, a different document \u2014 a bill of supply \u2014 is used instead, as explained below.<\/p>\n
Rule 46 of the CGST Rules, 2017 prescribes the particulars that a tax invoice must contain. While the exact layout is left to the business, the following contents are mandatory:<\/p>\n
A supplier must typically prepare a tax invoice in triplicate for goods (original for the recipient, duplicate for the transporter, triplicate for the supplier) and in duplicate for services. Businesses covered by e-invoicing must additionally report invoices to the Invoice Registration Portal and carry the resulting Invoice Reference Number and QR code.<\/p>\n
GST law prescribes several documents beyond the standard tax invoice. Using the correct one for each situation is essential for compliance.<\/p>\n
Issued by a regular registered supplier for taxable supplies of goods or services. It shows the tax charged separately and is the document on which the recipient claims ITC.<\/p>\n
A bill of supply is issued instead of a tax invoice where no tax can be charged to the recipient \u2014 that is, by a supplier making exempt supplies, or by a composition scheme taxpayer. Because no tax is charged, a bill of supply does not enable ITC. Composition dealers must also carry the words “composition taxable person, not eligible to collect tax on supplies” on the document.<\/p>\n
When a supplier receives an advance payment before the supply is made, a receipt voucher must be issued to acknowledge the advance. It records the amount received and, where the rate or nature of supply is not determinable, the law provides defaults for treating the advance.<\/p>\n
If an advance was received and a receipt voucher issued, but the supply does not subsequently take place and no invoice is raised, the supplier issues a refund voucher when returning the money to the recipient.<\/p>\n
Where a registered person is liable to pay tax under the reverse charge mechanism, a payment voucher must be issued at the time of making payment to the supplier. A recipient liable under reverse charge who buys from an unregistered supplier must also issue a self-invoice for the supply.<\/p>\n
A credit note is issued where the taxable value or tax on an already-issued invoice needs to be reduced (for example, a return or a post-supply discount), and a debit note where it needs to be increased. These adjust the original invoice rather than replace it.<\/p>\n
The time limit depends on whether the supply is of goods or services.<\/p>\n
The invoice number is a controlled field, not a free-form reference. Rule 46 requires a consecutive serial number that:<\/p>\n
A business may maintain more than one series (for example, by branch or document type), but each series must be internally consecutive and unique for the year. It is standard practice to reset the numbering at the start of each financial year, on 1 April, and to begin a fresh series. Gaps, duplicates or numbers exceeding the character limit are common causes of notices and reconciliation mismatches, so the numbering logic in your billing software should be reviewed at the start of every year.<\/p>\n