GST Invoice Format: Every Field the Rules Require

The GST invoice format is set by Rule 46 of the CGST Rules, which lists the particulars a tax invoice must carry — supplier and recipient details, a consecutive serial number, HSN or SAC, taxable value, the rate and amount of each tax head, place of supply and a signature. There is no prescribed template and no official form number: the law specifies the information, not the layout, so any document that carries every particular is a valid tax invoice regardless of how it looks.

The GST invoice format: what Rule 46 requires

Most disputes about invoices are not about design. They are about a missing field that only surfaces when the recipient tries to claim credit. Read the table below as the specification your billing system has to satisfy.

Two of these repay attention. Splitting the tax into separate heads matters because a single line reading "GST 18%" tells the recipient nothing about whether they are claiming IGST credit or a CGST and SGST pair, and the two behave differently in the ledger. And the number of HSN digits is not a matter of preference — it is driven by your aggregate turnover, and the digit requirement by turnover bracket has tightened over time, so a template built years ago may now be under-reporting.

The recipient GSTIN deserves the same scepticism. A typo, or a number that has since been cancelled, is not a cosmetic error: it breaks the credit chain and the invoice will not match in your customer’s GSTR-2B. Our explainer on how a GSTIN is constructed covers what each of the fifteen characters encodes, and the same reasoning underpins spotting a fabricated GST number before it reaches your books.

The serial number rules almost everyone gets wrong

The serial number is a short specification with unforgiving edges. Rule 46(b) requires a consecutive serial number, not exceeding sixteen characters, in one or multiple series, made up of alphabets, numerals or the two special characters hyphen and slash and any combination of those, and unique for a financial year.

Unpacking that gives four rules that between them cause most of the practical problems:

• Sixteen characters is a hard ceiling. Prefixes that encode branch, year, division and document type run out of room faster than people expect. INV/BLR/2026-27/000123 is twenty-one characters and therefore non-compliant.
• Only hyphen and slash are permitted. Underscores, hashes, full stops and spaces are not in the rule. Systems that generate INV_00123 are technically outside it.
• Consecutive means no gaps you cannot explain. Cancelled invoice numbers should be retained and marked cancelled rather than reissued to a different transaction.
• Unique for a financial year, and only the financial year. Restarting the series on 1 April is exactly what the rule contemplates. Restarting it mid-year, or in the middle of a series, creates duplicates within the same year and is not permitted.

Multiple concurrent series are allowed and are often the right answer — one per branch, or one for domestic sales and one for exports. The condition is that each series is consecutive within itself and no number repeats across the financial year, which usually means giving each series a distinct prefix. The same discipline applies to the numbering of a credit note or debit note, which has its own sixteen-character series under Rule 53.

When the invoice has to be issued

Section 31 sets deadlines that differ by what is being supplied, and the difference is not arbitrary. Goods move physically, so the invoice has to exist before they leave; services do not, so the law allows a window after the fact.

Goods

Where the supply involves movement of goods, the invoice must be issued before or at the time of removal for supply to the recipient. In every other case — goods delivered on site, or simply made available where they stand — it must be issued before or at the time of delivery or of making the goods available. There is no grace period. A consignment travelling without an invoice already in existence is a detention risk, quite apart from the GST consequences.

Services

An invoice for services may be issued before or after the service is provided, but within the period prescribed by Rule 47 — thirty days from the date of supply of the service. That gives month-end billing cycles room to work, which is exactly what it is for.

Banking, insurance and financial institutions

An insurer, a banking company, a financial institution or a non-banking financial company gets a longer window of forty-five days, on the reasoning that interest, fees and charges are computed on cycles that do not fit a thirty-day rule. Where such an entity makes taxable supplies to a distinct person — typically between its own registrations in different states — it may issue the invoice before or at the time of recording the supply in its books, or before the end of the quarter, whichever is earlier. Continuous supply has its own timing rules keyed to statements of account and contractual payment dates.

Triplicate for goods, duplicate for services

Rule 48 governs the number of copies, and the logic follows from whether anything physically moves.

The transporter copy exists so that the person carrying the goods can produce documentation on demand. Where a valid e-way bill has been generated for the consignment, that requirement is satisfied and a separate physical transporter copy is not insisted upon. The markings themselves are part of the rule, so a system that prints three identical copies without the ORIGINAL, DUPLICATE and TRIPLICATE labels has not quite complied.

How one field decides IGST or CGST plus SGST

The place of supply is the field that determines which tax you charge, and getting it wrong is the single most expensive invoice error in GST. The test is a comparison, not a lookup: put the location of the supplier next to the place of supply, and if the two are in different states or union territories the supply is inter-state and attracts IGST. If they are in the same state, it is intra-state and attracts CGST plus SGST in equal halves.

That is why Rule 46 makes the place of supply, along with the name of the state, a mandatory particular on inter-state invoices. The field is the justification for the tax head you have charged. It is also why the delivery address becomes a separate particular whenever it differs from the place of supply: in a bill-to-ship-to transaction the goods physically go to one state while the place of supply is deemed to be the location of the party who directed the movement, and the invoice has to show both facts.

Charging the wrong head is not a rounding error. The recipient cannot use IGST credit where CGST and SGST were due, or the reverse; you pay the correct tax and then claim a refund of the wrong one. The place of supply rules repay proper reading, particularly for services, where the default of the recipient location gives way to specific rules for immovable property, events, transport and telecom. Running the customer GSTIN through the GSTIN validator confirms the state code in the first two digits before it becomes a mis-stated place of supply.

When something other than a tax invoice is the right document

A tax invoice is only correct when tax is actually being charged. The GST scheme has a small family of substitute documents for the situations where it is not.

Bill of supply

Where the supply is exempt or nil-rated, or where the supplier is registered under the composition scheme and therefore cannot collect tax, a bill of supply replaces the tax invoice. It carries no tax rate and no tax amount, and it supports no input tax credit. Where a registered person supplies taxable and exempt goods or services together to an unregistered person, Rule 46A permits a single invoice-cum-bill-of-supply covering both rather than two documents for the same transaction.

Revised invoice

Registration takes effect from a date that is usually earlier than the date the certificate is actually issued, which leaves a gap during which you were registered but had no GSTIN to print. Section 31(3)(a) resolves it: you may issue a revised invoice, marked as such, against every invoice already raised in that window, within one month of the date the registration certificate was issued. For unregistered recipients a consolidated revised invoice is allowed, prepared state-wise for inter-state supplies above the value the rule specifies.

Vouchers and self-invoices

Three vouchers cover money moving without a supply having been invoiced, and a fourth document covers supply without a supplier who can invoice it:

• A receipt voucher is issued when an advance is received against a future supply.
• A refund voucher is issued when that advance is returned because the supply never happened and no tax invoice was raised against the receipt voucher.
• A payment voucher is issued by a recipient who is liable to pay tax under reverse charge, at the time of paying the supplier.
• A self-invoice is issued by a registered recipient who receives a notified supply from an unregistered supplier under reverse charge. Because the supplier cannot raise a GST invoice, the recipient raises one to itself, and that document is what supports the credit.

E-invoicing, the IRN and the QR code

For businesses above the notified aggregate turnover, the invoice is no longer complete when it is printed. Rule 48(4) requires a notified class of registered persons to prepare the invoice by uploading its particulars in Form GST INV-01 to the Invoice Registration Portal, which validates them, returns an Invoice Reference Number — a hash derived from the supplier GSTIN, the invoice number, the document type and the financial year — and embeds the IRN in a signed QR code that must be printed on the document.

Rule 48(5) then does something unusually blunt. Any invoice issued by such a person in a manner other than the one specified in 48(4) shall not be treated as an invoice. Not defective, not irregular: not an invoice. The supply is treated as made without an invoice, the recipient has nothing to support credit against, and the exposure sits on both sides of the transaction.

Two operational points follow. First, the turnover threshold has come down in stages, so a business comfortably outside it one year can be inside it the next — treat the current e-invoicing threshold and how it is computed as something to re-check each year against the governing notification rather than assume. Second, larger taxpayers face a reporting time limit: invoices must be uploaded within a fixed number of days of the document date, after which the portal refuses them and no IRN can be obtained at all. Confirm both the threshold and the reporting window against the e-invoice portal advisories and the relevant CBIC notification before configuring your billing system.

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