GST Invoice Requirements — What Every Business Must Know

A properly formatted GST invoice is the foundation of the entire GST compliance chain. Mistakes in invoicing can lead to ITC rejection, penalties, and compliance complications for both the seller and buyer. ## Mandatory Fields in a GST Invoice Every GST invoice must contain specific information to be considered valid. The invoice must include sequential invoice number (up to 16 characters, alphanumeric), date of issue, customer name and address, customer GSTIN (if registered), place of supply with state name, billing and shipping addresses if different, HSN codes for goods or accounting codes for services, and description of goods or services with quantity and unit. The tax breakdown must separately show taxable value, CGST, SGST/UTGST, and IGST as applicable, with applicable tax rates. For exports, invoice must show "Zero Rated Supply" with a note that LUT/Bond has been furnished. Discounts and free samples have specific invoice treatment requirements. ## Invoice Numbering Requirements The invoice number must be unique for each financial year and sequential. You cannot restart numbering at 1 for each month — you must maintain continuous numbering throughout the year. Most businesses use a format like INV-2024-001, INV-2024-002, making audit trails straightforward. Revising or amending invoices requires issuing a Credit Note (for sales returns or price adjustments) or Debit Note (for additional claims). Credit and Debit Notes must reference the original invoice number and are reported in GSTR-1 with adjustments made in the period they are issued. ## Different Invoice Types Tax Invoice is the standard invoice for B2B sales to registered persons, containing all mandatory fields including buyer GSTIN. This enables the buyer to claim input tax credit. Receipt voucher is issued when a payment is received, followed by a tax invoice later when goods are delivered. This handles advance payments where GST is payable at the time of receipt even if goods are not yet delivered. ## E-Invoice Requirements Businesses with turnover exceeding Rs 10 crore must generate e-invoices through the government's e-invoice portal (einvoice.gst.gov.in). The e-invoice system auto-generates an Invoice Reference Number (IRN) after validating the invoice details against GST rules. E-invoices integrate with the e-way bill system for movement of goods and GSTR-1 for filing returns. The IRN must be included on the invoice, and the QR code contains machine-readable invoice data that tax authorities can scan for verification.