GST Invoice Format in India: Every Mandatory Field

The mandatory fields under Rule 46

Rule 46 of the CGST Rules sets out what a tax invoice must contain. The list below is what a compliant invoice carries. Where a field does not apply — an unregistered buyer has no GSTIN, for instance — the rule provides for that, but you cannot simply omit fields that do apply.

The CBIC GST portal publishes the rules and notifications directly, and is the authority worth checking when something changes.

• The words "Tax Invoice" clearly on the document
• Your name, address and GSTIN
• A consecutive serial number, maximum 16 characters, unique within the financial year
• The date of issue
• The recipient's name, address and GSTIN, where they are registered
• For unregistered recipients above ₹50,000, their name, address and delivery state
• HSN code for goods, or SAC code for services
• Description of the goods or services
• Quantity and unit of measure
• Total taxable value of the supply
• The rate of tax, split into CGST, SGST/UTGST, IGST and cess as applicable
• The amount of tax charged, again split by head
• Place of supply, with the state name, for inter-state supplies
• Delivery address, where it differs from the place of supply
• Whether tax is payable on a reverse charge basis
• Signature or digital signature of the supplier or an authorized representative

CGST + SGST or IGST? Place of supply decides

This is where most invoices go wrong, and the error is expensive because the buyer cannot claim credit for the wrong tax head.

The test is not where you are. It is the place of supply relative to your location. If both fall in the same state, the tax splits into CGST and SGST at half the rate each. If they fall in different states, you charge IGST at the full rate.

A supplier in Mumbai billing a buyer in Delhi charges IGST. If that supplier charges CGST and SGST instead, the Delhi buyer cannot claim it — Delhi has no share of Maharashtra's state tax — and will come back asking for a corrected invoice.

For services, place of supply is generally the recipient's location where they are registered. There are specific rules for immovable property, events, transport and several other categories, so check the provision that covers your supply rather than assuming the general rule.

How many HSN or SAC digits you need

HSN codes classify goods; SAC codes classify services. How many digits you must show depends on your aggregate turnover in the preceding financial year, and the thresholds have tightened over time.

Businesses below ₹5 crore turnover show 4 digits on B2B supplies. Businesses above ₹5 crore show 6 digits. Exports and imports require the full 8-digit code regardless of turnover.

Getting the code wrong is not a formatting issue — it determines the rate. If you are unsure which code applies to what you sell, the classification is worth confirming with your accountant once and then reusing, rather than guessing per invoice.

Invoice numbering rules that catch people out

GST numbering is stricter than general commercial practice, and the constraints are worth knowing before you design a scheme.

The serial number is capped at 16 characters. It may contain letters, numerals, hyphens and slashes only. It must be consecutive, and it must be unique within the financial year — which means most businesses reset their sequence each April rather than running one continuous series.

A common working scheme is a short prefix, the financial year and a running number: INV/25-26/001. That fits comfortably inside 16 characters and makes the year obvious on the face of the document.

Gaps in the sequence attract questions during assessment. If you cancel an invoice, do not reuse or skip the number — issue a credit note against it instead, as covered in credit notes and refunds.

E-invoicing: who it applies to

E-invoicing under GST means generating your invoice on your own system, then reporting it to the Invoice Registration Portal, which returns an Invoice Reference Number and a QR code. The invoice is only valid once it carries them.

The turnover threshold has been lowered in stages since the scheme began, and it has reached businesses well below the levels it started at. Because the threshold has moved repeatedly, check the current figure on the GST portal rather than relying on a number quoted in an article — including this one.

If you are below the threshold, you issue an ordinary tax invoice and nothing changes. If you are above it, an invoice without an IRN is not a valid tax invoice, and your buyer cannot claim credit against it.

GST invoice questions, answered

Sources

1. CGST Rules and notifications — Central Board of Indirect Taxes and Customs
2. GST portal tutorials and e-invoicing guidance — Goods and Services Tax Network

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