GST Bill Format: What a Valid GST Invoice Must Contain (2026)

A GST invoice is not just a receipt — it is the legal document that lets your buyer claim input tax credit and proves you charged tax correctly. Get the format wrong and your customer's ITC can be denied, which quickly becomes your problem. The good news is that a valid GST bill follows a fixed recipe. This 2026 guide lays out every mandatory field, the numbering rules, when to use a bill of supply instead, the time limits for issuing an invoice, and how B2B and B2C invoices differ — with a described example you can copy.

Why the format matters

Under GST, a tax invoice is the document on which the whole credit chain runs. Your buyer uses it to claim ITC; the tax department uses it to match returns; and you use it to prove compliance in an audit. An invoice missing mandatory fields is not just untidy — it can be treated as invalid, putting your customer's credit and your own standing at risk. If you are new to invoicing generally, our primer on what an invoice is and its types is a good starting point.

Mandatory fields of a GST tax invoice

A valid tax invoice must carry all of the following:

1. Supplier details. Your business name, full address, and GSTIN.
2. Invoice number and date. A unique consecutive serial number (up to 16 characters) and the date of issue.
3. Buyer details. The recipient's name and address, and — for a B2B supply — their GSTIN. For B2C above the threshold, the delivery address and state are needed.
4. HSN or SAC code. The Harmonised System of Nomenclature code for goods, or the Services Accounting Code for services, at the digit level required for your turnover.
5. Description, quantity and unit. A clear description of each item, quantity and unit of measure.
6. Taxable value. The value of the supply after any discount, on which tax is charged.
7. Tax rate and amount. The applicable rate and the tax split — CGST and SGST/UTGST for intra-state supplies, or IGST for inter-state supplies — plus cess where applicable.
8. Place of supply. Required especially for inter-state supplies, as it determines whether CGST/SGST or IGST applies.
9. Reverse charge indication. A clear note if the tax is payable on reverse charge by the recipient.
10. Signature. The signature or digital signature of the supplier or an authorised representative.

Invoice numbering rules

The serial number is not decorative — it has rules:

• It must be unique and consecutive for the financial year.
• It can be up to 16 characters long.
• Only letters, numbers, and the symbols dash and slash are allowed.
• You may run multiple series — for example a separate series per branch or per document type — as long as each series is consecutive and clearly traceable.

A common, clean pattern is something like INV/2026-27/0001, incrementing by one for each invoice. Gaps and duplicates draw scrutiny, so a system that auto-numbers for you removes an entire category of error.

When to use a bill of supply instead

Not every sale carries GST. In two situations you issue a bill of supply rather than a tax invoice:

• You are a composition-scheme dealer, who cannot collect GST from customers.
• You are supplying exempt goods or services.

A bill of supply looks similar but shows no tax rate and no tax amount, because none is charged. Composition dealers must also print the note that they are a composition taxable person not eligible to collect tax on supplies. Mixing these up — putting a tax breakup on a bill of supply, or omitting tax on what should be a tax invoice — is a compliance error.

Time limits to issue an invoice

You cannot issue an invoice whenever you feel like it:

• Goods: issue on or before the removal or delivery of the goods to the buyer.
• Services: issue within 30 days of supplying the service (45 days for banks and financial institutions).

Issuing late, or not at all, is a breach that can attract penalty and, more practically, delays your customer's ITC and your own revenue recognition.

B2B vs B2C invoices

The difference comes down to who the buyer is and whether they need credit:

• B2B (business to business). The buyer is GST-registered and wants ITC, so a full tax invoice with their GSTIN is mandatory, and these invoices are reported individually in GSTR-1.
• B2C (business to consumer). The buyer is an end consumer who does not claim ITC. For small-value B2C sales you may issue a simplified invoice or, below the threshold, none unless asked — but you must maintain a consolidated record and report B2C sales in summary.

Because B2B invoices feed your buyers' credit, they demand the most care. A wrong GSTIN or a missing HSN on a B2B bill directly blocks your customer's ITC.

How many copies, and paper vs digital

The rules also specify how many copies of a tax invoice to prepare. For a supply of goods, three copies are made — the original for the recipient, a duplicate for the transporter, and a triplicate for the supplier. For a supply of services, two copies suffice — original for the recipient and a duplicate for the supplier. A digitally signed or e-invoiced PDF is perfectly valid, so a software-generated invoice with the required fields and a digital signature meets the requirement without any printing. What matters is not paper versus screen but that every mandatory field is present and the document is authenticated.

Related documents you may also issue

A tax invoice is the main document, but GST recognises a small family of related documents, each with its own use:

• Credit note. Issued when the taxable value or tax on an earlier invoice needs to be reduced — a return, a discount, or an overcharge. It lowers your output tax.
• Debit note. Issued when the value or tax on an earlier invoice needs to increase — an undercharge or an extra supply. It raises your output tax.
• Receipt voucher. Issued when you receive an advance payment before the supply is made.
• Delivery challan. Used to move goods where a tax invoice cannot yet be issued — for job work, or supply on approval.

Credit and debit notes must reference the original invoice and are reported in GSTR-1, so keep them numbered and linked rather than adjusting old invoices after the fact.

E-invoicing: when the portal generates an IRN

Businesses above the notified turnover threshold must generate an e-invoice — the invoice is reported to the government's Invoice Registration Portal, which returns a unique Invoice Reference Number (IRN) and a QR code that must be printed on the bill. E-invoicing does not change the fields your invoice needs; it adds a validation and reporting layer on top. Smaller businesses below the threshold issue ordinary tax invoices as described here, but the format discipline is identical, so building the habit now means you are ready if your turnover crosses the line later.

A described example layout

Picture a standard A4 GST tax invoice. Across the top sits your business name, address and GSTIN, with the words Tax Invoice clearly labelled. On the upper right, the invoice number and date. Below that, two blocks side by side: Bill To with the buyer's name, address and GSTIN, and Place of Supply with the state and its code.

The body is a table with columns for description, HSN/SAC, quantity, rate, taxable value, and then the tax columns — CGST rate and amount, SGST rate and amount (or a single IGST pair for inter-state). Under the table, a totals block adds up the taxable value and each tax head to the grand total, often with the amount in words. A footer notes whether reverse charge applies, any terms, and carries the authorised signature. That is a compliant GST bill — every required field in a layout your customer and the department both recognise instantly.

Once you have this template internalised, invoicing is quick and dependable. And once you need to pay the tax you have collected on these invoices, our guide to GST payment and creating a challan online takes it from there. Get the invoice right at the source, and everything downstream — ITC, returns, payments — falls into place.