GST Invoice Format: A Complete Guide

Published on: July 29, 2026

A GST invoice is not a design decision. It is the legal document that fixes your output tax liability, decides whether your customer can claim Input Tax Credit (ITC), and travels with your goods through every check post. Section 31 of the CGST Act, 2017 makes issuing it compulsory, and Rule 46 of the CGST Rules, 2017 prescribes exactly what it must contain. Miss a particular, and the document stops being a tax invoice in the eyes of the law.

The stakes are practical rather than theoretical. India has more than 1.5 crore registered GST taxpayers, and invoice-level data now flows automatically from your billing software into GSTR-1, your buyer's GSTR-2B and the Invoice Management System (IMS). Every mismatch surfaces in a system-generated notice. Section 122(1) prescribes a penalty of ₹10,000 or the tax evaded, whichever is higher, for supplies made without an invoice or with an incorrect one.

This guide sets out the complete GST invoice format for FY 2026-27: the mandatory Rule 46 particulars, HSN digit requirements, numbering rules, which document to use when, the additional requirements for e-invoicing taxpayers, and the special lines needed for exports, reverse charge and SEZ supplies.

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What is a GST invoice, and when must you issue one?

A GST invoice is the tax document a registered supplier must issue under Section 31 for every taxable supply of goods or services. For goods, issue it before or at the time of removal or delivery. For services, issue it within 30 days of supplying the service — extended to 45 days for banks, NBFCs and insurers under Rule 47.

Timing rules that trip up growing businesses:

• Continuous supply of goods: issue an invoice on or before each statement of accounts or each receipt of payment
• Continuous supply of services: issue by the due date of payment where it is ascertainable from the contract, or when payment is received where it is not
• Reverse charge purchases from unregistered suppliers: raise a self-invoice within 30 days of receiving the supply, as required by Section 31(3)(f) read with Rule 47A
• Goods sent on approval: issue before or at the time of supply, or six months from removal, whichever is earlier
• Advances received for services: issue a receipt voucher under Rule 50, not a tax invoice

Rule 48(1) also fixes the number of copies: goods invoices in triplicate (original for the recipient, duplicate for the transporter, triplicate for the supplier) and services invoices in duplicate (original for the recipient, duplicate for the supplier). Taxpayers covered by e-invoicing satisfy this through the digital record instead.

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Which fields are mandatory under Rule 46 of the CGST Rules?

Rule 46 lists sixteen particulars. A document that omits any applicable field is not a valid tax invoice, which means your buyer's ITC claim under Section 16(2)(a) is exposed. Build your template clause by clause rather than copying a vendor sample.

Two provisos matter for larger taxpayers. Rule 46(r) requires a QR code carrying the Invoice Reference Number on e-invoices, and Rule 46(s) requires a specific declaration on invoices where the supplier has crossed the notified turnover but is not obliged to generate an e-invoice.

Test your template against this list once a year. Software upgrades, new branches and custom print formats are the usual reasons a compliant invoice quietly becomes non-compliant.

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How many HSN or SAC digits must your invoice carry?

HSN reporting is turnover-linked. Businesses with aggregate annual turnover up to ₹5 crore must report at least 4 digits on B2B invoices, and businesses above ₹5 crore must report 6 digits on all invoices. Exports, imports and a notified list of chemical products require 8 digits irrespective of turnover.

Related reporting points:

• HSN summary in GSTR-1 Table 12 is now a dropdown-driven, validated field — free-text HSN entries no longer pass, so the master data in your billing system must be clean
• Services always require the correct SAC, and a wrong SAC is the most common cause of rate disputes in professional services billing
• Classification drives rate. If your product moved slabs during the rate rationalisation, revisit the mapping before printing invoices — our explainer on GST 2.0 slab changes covers the migration, and the complete GST rate list sets out current rates

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How should you set up your invoice numbering for FY 2026-27?

Rule 46(b) requires a consecutive serial number, unique for the financial year, of not more than 16 characters, using only alphabets, numerals and the special characters hyphen, dash and slash. In practice this means a fresh series from 1 April 2026 and separate series for each GSTIN, branch and document type.

A numbering scheme that survives audit:

• Format: something like INV/2627/DEL/00001 — entity or branch code, financial year, running number
• One series per document type: tax invoices, credit notes, debit notes, delivery challans and bills of supply must not share a series
• No gaps and no reuse: cancelled numbers must be recorded as cancelled, not reissued. Serial breaks are a standard audit query and an ITC risk for your buyer
• Duplicate control: the Invoice Registration Portal rejects a repeat combination of GSTIN, document type, document number and financial year, so accidental reuse blocks your IRN
• Branch discipline: if you have multiple GSTINs, never let two locations issue the same number under the same PAN-linked series logic

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Tax invoice, bill of supply, or a voucher — which document applies?

Not every transaction needs a tax invoice. The CGST Rules prescribe a distinct document for each situation, and using the wrong one is treated as a documentation failure even where the tax outcome is neutral.

A composition taxpayer must also carry the declaration that they are a composition taxable person and not eligible to collect tax on supplies. A registered person supplying exempt goods or services should never show a tax rate on a bill of supply.

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What changes if you are covered by e-invoicing?

If your aggregate annual turnover crossed ₹5 crore in any financial year from FY 2017-18 onwards, you must generate invoices under Rule 48(4) by reporting them to an Invoice Registration Portal (IRP) in FORM GST INV-01 and printing the resulting Invoice Reference Number (IRN) and signed QR code. Under Rule 48(5), an invoice issued without an IRN is not an invoice at all.

What this changes on the document itself:

• The IRN and the signed QR code must appear on the printed or shared copy
• A physical signature is not required where a valid IRN exists
• The invoice cannot be edited after the IRN is generated. Cancellation is allowed on the IRP within 24 hours; later corrections go through a credit note or an amendment in GSTR-1
• Taxpayers with AATO of ₹10 crore and above must report the document to the IRP within 30 days of the invoice date
• Suppliers above the notified turnover who are exempt from e-invoicing must print the Rule 46(s) declaration

For the full workflow, exclusions and portal mechanics, read E-invoicing under GST and our side-by-side comparison in E-invoice vs Regular Invoice.

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Export, SEZ, reverse charge and e-commerce: what extra lines do you need?

Special supplies need extra particulars on the face of the invoice. An export invoice must carry a specific endorsement, a reverse-charge invoice must state that tax is payable by the recipient, and SEZ supplies must identify the unit or developer. These are format requirements, not optional notes.

• Exports and SEZ supplies: endorse either "SUPPLY MEANT FOR EXPORT ON PAYMENT OF INTEGRATED TAX" or "SUPPLY MEANT FOR EXPORT UNDER BOND OR LETTER OF UNDERTAKING WITHOUT PAYMENT OF INTEGRATED TAX", along with the recipient's name, address and country of destination and the delivery address
• Currency and conversion: show the invoice currency and, where required, the rupee equivalent. File a fresh Letter of Undertaking for FY 2026-27 before your first zero-rated invoice
• Reverse charge supplies: print "Tax payable on reverse charge basis" and do not charge tax on the invoice
• Bill-to ship-to transactions: complete both Rule 46(d) and Rule 46(o) — the registered buyer's details and the actual delivery address
• E-commerce sales: reconcile portal-generated invoices with your own series, and check the TCS credit reflected by the operator
• Goods in transit: an invoice or delivery challan must accompany the consignment along with the e-way bill where the consignment value exceeds the prescribed limit

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What are the penalties for a defective GST invoice?

Invoice failures are penalised directly. Section 122(1) imposes ₹10,000 or the amount of tax evaded, whichever is higher, for supplying without an invoice, issuing an incorrect or false invoice, or issuing an invoice without a supply. Section 125 adds a general penalty of up to ₹25,000 where no specific penalty is prescribed.

The commercial consequences usually exceed the penalty:

• ITC denial for your buyer under Section 16(2)(a), which quickly becomes a payment dispute and a debit note demand
• Detention and seizure of goods in transit under Section 129 where documents are missing or defective
• Invalid invoice under Rule 48(5) where e-invoicing applied but no IRN was generated, which also blocks the e-way bill
• Interest under Section 50 where the correction results in short payment of tax
• Blocked returns where GSTR-1 and GSTR-3B do not reconcile with GSTR-2B and IMS actions taken by your customers

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Practical recommendations for FY 2026-27

1. Run a Rule 46 template audit in the first week of the financial year. Print one invoice of each type — B2B, B2C, export, SEZ, reverse charge — and tick every clause
2. Start a clean series on 1 April for every GSTIN, branch and document type, and lock the format in your ERP so users cannot override it
3. Fix HSN and SAC masters before the first GSTR-1 of the year. Validate against the Table 12 dropdown list rather than free text
4. Automate the IRN step at the point of billing if you are covered by Rule 48(4). Manual uploads are the leading cause of missed 30-day windows
5. Reconcile issued invoices to GSTR-1 monthly, and to your bank receipts, so gaps in the series are caught within the month — our monthly financial checklist sets out the cadence
6. Train the billing desk on the ₹50,000 B2C rule, place of supply and bill-to ship-to fields. Most defects originate at data entry, not in the tax logic
7. Document your credit note process so price revisions and returns flow through Section 34 rather than through manual invoice edits
8. Keep a retention plan for invoices and related records for the statutory period, with the audit trail intact in your accounting software

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References

1. CBIC — CGST Rules, 2017 (consolidated) — Rule 46 particulars, Rules 47 to 55 for special documents
2. GST Portal — Return formats, HSN reporting in GSTR-1 Table 12, taxpayer advisories
3. CBIC — Notification No. 78/2020-Central Tax — HSN digit requirements by turnover
4. CBIC — Notification No. 10/2023-Central Tax — ₹5 crore e-invoicing threshold
5. ClearTax — GST invoice format and rules — Field-by-field template guidance
6. TaxGuru — Invoicing provisions under GST — Analysis of Section 31 and Rule 46
7. e-Invoice Portal — IRN, QR code and schema documentation
8. Taxmann — CGST Act bare provisions — Sections 31, 34, 122 and 125