GST Invoice Format: Free Template + What’s Mandatory in 2026

A GST invoice is more than a bill - it is a legal document that lets your buyer claim input tax credit (ITC) and keeps your business compliant with GST law. Get the format wrong and your customer’s ITC can be denied, while you risk mismatches and notices. This 2026 guide walks through every mandatory field, when to issue the invoice, the e-invoicing rules, and where to find a free GST invoice template.

Tax invoice vs Bill of Supply

Issue a tax invoice when you supply taxable goods or services as a regular GST-registered dealer. Issue a Bill of Supply instead when you are a composition-scheme dealer, or you supply exempt or nil-rated goods - in those cases you cannot charge GST, so no tax is shown.

Mandatory fields under Rule 46

• A consecutive, unique invoice number (max 16 characters; letters, numbers, "/" and "-" allowed) for the financial year
• Date of issue
• Your name, address and GSTIN (the supplier)
• Customer name, address and GSTIN (if registered); for B2C above 50,000 rupees also the delivery address and state
• Place of supply and its state code
• HSN code for goods or SAC code for services
• Description, quantity, unit and taxable value of each line item
• Discount (if any) and the taxable value after discount
• Rate and amount of CGST, SGST/UTGST, IGST and cess - shown separately
• Total invoice value, and a clear note if tax is payable under reverse charge
• Signature or digital signature of the supplier (not required if a valid e-invoice IRN is generated)

The invoice number must be unique for the whole financial year. Resetting the series each year is fine and expected - reusing or skipping numbers within the same year is not.

When to issue the invoice

For goods, raise the invoice on or before the goods are removed or delivered. For services, raise it within 30 days of providing the service. Late or back-dated invoices are a common cause of return mismatches - make the invoice part of the moment of supply, not an afterthought.

Intra-state vs inter-state

If the place of supply is in your state, charge CGST + SGST (half the rate each). If it is in a different state, an SEZ or an export, charge IGST at the full rate. The place of supply - not the billing address alone - decides the tax.

HSN / SAC and the right GST rate

• Turnover up to 5 crore - at least 4 digits of HSN on B2B invoices
• Turnover above 5 crore - at least 6 digits on all invoices
• Exports and imports - 8 digits

The code drives the GST rate. Store HSN/SAC against each item once and it fills automatically on every future invoice.

E-invoicing (IRN and QR code)

If your aggregate turnover crosses the e-invoicing threshold (5 crore in recent years), B2B invoices must be reported to the government’s Invoice Registration Portal (IRP), which returns a signed IRN and a QR code. An invoice that needs an IRN but does not have one is not legally valid, and your buyer cannot claim ITC on it. Large taxpayers must report invoices to the IRP within a fixed window (e.g. 30 days) of the invoice date.

Reverse charge

On certain supplies the buyer, not the seller, pays the GST. When reverse charge applies, the invoice must say so explicitly, and you do not collect the tax from the customer. Flag these correctly so they land in the right boxes of your GSTR-1 and GSTR-3B.

Common mistakes to avoid

• Charging CGST/SGST on an inter-state sale (or IGST on an intra-state one)
• Missing or wrong place-of-supply state code
• Reusing or skipping invoice numbers within a financial year
• Leaving out the HSN/SAC code, or showing too few digits for your turnover
• Rounding tax per line instead of on the total taxable value
• Forgetting to generate the IRN/QR code when e-invoicing applies
• Charging GST on a Bill of Supply (composition / exempt supplies)

A free GST invoice template

Aveon GST generates a compliant GST invoice PDF with every required field - your GSTIN, customer GSTIN, place of supply, HSN/SAC, CGST/SGST/IGST split and round-off - in your chosen layout (Classic, Modern Minimal, Detailed GST or Professional). The free Starter plan covers this end to end; you do not need a separate Word or Excel template if you bill from the cloud.