GST invoice format explained — mandatory fields, CGST/SGST vs IGST, GSTIN rules — plus a free GST invoice generator.
A GST invoice is a tax invoice that a GST-registered business must issue, showing the supplier's and buyer's GSTIN, invoice number and date, HSN/SAC codes, taxable value, and the GST split (CGST + SGST for intra-state, or IGST for inter-state). Here's the format, the mandatory fields, and the intra- vs inter-state tax logic.
⚠️ General guidance only — not tax or legal advice. Verify with a professional and current GST rules before relying on any of this for filing.
What Is a GST Invoice?
If you're registered under GST in India and supplying taxable goods or services, you're required to issue a tax invoice in the prescribed format for every taxable supply. This document does two jobs simultaneously: it's the commercial record of the sale, and it's the legal document that lets your buyer claim input tax credit (ITC) on the GST they've paid you. Get the format wrong, or leave out a mandatory field, and your buyer's ITC claim can be rejected — which is exactly the kind of friction that damages a business relationship over what should be a routine administrative document.
This matters more than it might seem for a fairly mundane compliance requirement. A buyer who can't reliably claim ITC from your invoices has a real financial incentive to source from a supplier whose invoicing is cleaner — for a B2B seller, correct GST invoicing is quietly a competitive factor, not just a box to tick for your own filing.
Who Needs to Issue a GST Invoice?
Any business registered under GST, supplying taxable goods or services above the registration threshold (or voluntarily registered), must issue GST-compliant tax invoices for every sale. Unregistered small businesses below the threshold issue regular invoices without GST — but the moment you cross the threshold or register voluntarily, every invoice needs to follow the tax invoice format below. Composition scheme dealers issue a bill of supply instead of a tax invoice (since they don't charge GST separately) — a distinction worth flagging if you're unsure which category you fall into. ⚠️CHECK the current threshold and composition-scheme rules against official CBIC guidance for your specific situation.
Mandatory Fields on a GST Invoice ⚠️CHECK
- Supplier's name, address, and GSTIN
- A unique, sequential invoice number (per financial year)
- Date of issue
- Buyer's name, address, and GSTIN (if registered)
- Place of supply (state) — this determines CGST/SGST vs IGST
- HSN code (goods) or SAC code (services)
- Description, quantity, unit, and taxable value of each item
- Rate and amount of GST (CGST, SGST/UTGST, IGST as applicable)
- Total invoice value
- Whether tax is payable on reverse charge
- Signature (or digital signature) of the supplier
Missing even one of these — most commonly the HSN/SAC code, or a correct place-of-supply state — is the single most common reason a GST invoice gets flagged during a buyer's reconciliation or an audit.
HSN and SAC Codes, Explained
HSN (Harmonised System of Nomenclature) codes classify goods, while SAC (Services Accounting Code) classifies services — both exist so that tax authorities and trading partners across the world use a consistent classification for what's actually being sold, regardless of how the seller happens to describe it in plain language. The number of HSN/SAC digits you're required to show generally depends on your business's turnover, with larger businesses required to show more digits than small ones. ⚠️CHECK the current digit-count thresholds against official rules, since these have been revised in the past and are exactly the kind of detail that's easy to get out of date on. If you don't already know your product or service's correct code, look it up rather than guessing — an incorrect HSN/SAC code is a common reconciliation mismatch that can hold up a buyer's ITC claim even when every other field on the invoice is correct.
CGST/SGST vs IGST — the Key Rule
- Intra-state (supplier and place of supply in the same state): charge CGST + SGST (split equally, so an 18% rate becomes 9% CGST + 9% SGST).
- Inter-state (supplier and place of supply in different states): charge IGST at the combined rate (18% IGST, in the same example).
Example: an 18% GST item sold within the same state = 9% CGST + 9% SGST on the invoice, shown as two separate line items. The same item sold to a buyer in another state = 18% IGST, shown as one line item. This is why "place of supply" — not simply where your business is registered — is the field that actually determines the split; get the place of supply wrong and you'll charge the wrong tax structure even if your rate is correct.
Reverse Charge Mechanism (RCM)
Under certain categories of supply, GST liability shifts from the supplier to the buyer — this is the reverse charge mechanism, and it must be explicitly stated on the invoice when it applies (field 10 in the mandatory list above). Common reverse-charge scenarios include specified categories of services from unregistered suppliers and certain notified goods/services. ⚠️CHECK the current list of reverse-charge categories, since this list is set by notification and can change — never assume a transaction is or isn't RCM without checking the current rules against your specific supply category.
GST Invoice for Services vs Goods
The core mandatory fields are the same for both, with one practical difference worth noting: for services, invoices generally must be issued within a specified period of supplying the service, whereas for goods, the invoice is typically issued at or before the time of delivery/removal. ⚠️CHECK current timeline rules for your specific case. For services, you'll also use SAC codes rather than HSN codes, and there's no "quantity" in the traditional sense — a services invoice line item is usually described by scope (e.g., "consulting services — March 2026") rather than a countable unit.
Invoice Numbering Rules ⚠️CHECK
- Must be unique and consecutive within a financial year.
- Generally up to 16 characters, which can include letters, numbers, and specific symbols like hyphens and slashes.
- A common, compliant pattern is a prefix plus financial year plus sequence — for example,
INV/2026-27/001.
Restarting your numbering at the start of each new financial year is standard practice and expected — just make sure the sequence itself never repeats or skips within that year.
Export Invoices and Zero-Rated Supply
Exports of goods or services are generally treated as zero-rated supply under GST, meaning GST is charged at 0% (rather than being exempt), and the invoice needs to reflect this along with the relevant export documentation requirements — typically noting whether the export is under a Letter of Undertaking (LUT) or with IGST payment and subsequent refund claim. ⚠️CHECK current export invoicing rules if you're supplying internationally, since export compliance carries its own separate documentation requirements beyond the standard domestic tax invoice fields above.
Credit Notes and Debit Notes
When an invoice needs correction after issue — a return, a discount applied after the sale, or a billing error discovered later — the correct approach under GST isn't to edit or delete the original invoice, but to issue a credit note (reducing the amount owed) or debit note (increasing it), referencing the original invoice number. This preserves your invoice sequence intact and gives both parties a clean audit trail of exactly what changed and why, rather than a silently edited original that no longer matches what was actually recorded at the time.
E-Invoicing Requirements
Businesses above a certain turnover threshold are required to generate e-invoices through the government's e-invoicing system, which validates the invoice and issues an Invoice Reference Number (IRN) and QR code that must appear on the invoice. ⚠️CHECK the current e-invoicing turnover threshold, since this has been progressively lowered over time to cover more businesses. If e-invoicing applies to you, a manually created PDF invoice without the IRN and QR code isn't compliant — this is a separate, additional requirement layered on top of the standard tax invoice format above, not a replacement for it.
Common GST Invoice Mistakes
- Missing or wrong HSN/SAC codes — the most frequent reconciliation issue on the buyer's side.
- Wrong place of supply, leading to CGST/SGST charged when IGST was owed, or vice versa.
- Non-sequential or duplicate invoice numbers, which raises red flags in any audit or reconciliation.
- Rounding the total without showing the underlying tax math, which makes an invoice harder to verify and more likely to be queried.
- Editing a sent invoice instead of issuing a proper credit or debit note, breaking the audit trail.
- Forgetting the reverse-charge note on invoices where RCM applies.
GST Invoices and Your GST Returns
Every tax invoice you issue as a supplier, and every one you receive as a buyer, needs to reconcile against your periodic GST return filings — this is the whole point of the mandatory fields above: they're not arbitrary formatting rules, they're what lets your outward supplies (sales) and your buyer's inward supplies (purchases) match up automatically in the government's reconciliation system. A mismatch between what you report as a sale and what your buyer reports as a purchase — often caused by an incorrect GSTIN, a wrong invoice number, or a mismatched taxable value — is one of the most common reasons an input tax credit claim gets held up or queried. Getting the invoice right the first time avoids a much more time-consuming correction process during return filing.
A Worked Example: Intra-State vs Inter-State
Say you're a Delhi-based consultancy invoicing a client for ₹50,000 in services at 18% GST.
- Client also in Delhi (intra-state): Taxable value ₹50,000 + CGST 9% (₹4,500) + SGST 9% (₹4,500) = total ₹59,000, shown as two separate tax lines on the invoice.
- Client in Maharashtra (inter-state): Taxable value ₹50,000 + IGST 18% (₹9,000) = total ₹59,000, shown as a single IGST line.
Notice the total invoice value is identical either way — it's only the breakdown of how that 18% is split that changes based on the place of supply. This is exactly why place of supply, not your own registered state alone, is the field that actually drives the correct tax treatment.
GST Invoice QR Codes and E-Invoicing in Practice
For businesses above the e-invoicing turnover threshold, the invoice isn't considered valid until it's been registered through the government's Invoice Registration Portal (IRP) and returned with an Invoice Reference Number (IRN) and a signed QR code embedded on the document. In practice, this means the sequence is: generate the invoice → submit it to the IRP → receive the IRN and QR code back → add both to the final invoice before sending it to your buyer. Skipping this step for a business above the threshold means the invoice technically isn't compliant, even if every other field on it is correct. ⚠️CHECK your current turnover status against the applicable e-invoicing threshold, since it has been revised downward over time to cover progressively smaller businesses.
Bill of Supply vs Tax Invoice: A Direct Comparison
It's worth being precise about when each document applies, since confusing the two is a common beginner mistake for a newly registered business. A tax invoice is issued whenever GST is charged separately on a taxable supply — this is the standard document described throughout this guide, and it's what supports the buyer's input tax credit claim. A bill of supply is issued instead when GST isn't charged separately — this applies to composition-scheme dealers (who pay tax at a fixed rate on turnover rather than charging it per invoice) and to supplies that are exempt from GST entirely. A bill of supply carries most of the same identifying fields (supplier and buyer details, a unique number, the date, itemized description) but explicitly does not show a tax amount, since none is being charged on that specific document. ⚠️CHECK which category your registration falls under before assuming either format applies by default.
GST Invoice Mistakes That Specifically Delay ITC Claims
Beyond the general mistakes listed above, a few errors specifically hold up your buyer's ability to claim input tax credit, which makes them worth flagging separately: invoicing under the wrong GSTIN (using an old or mistyped number), a taxable value that doesn't match what was actually agreed or delivered, and filing your own GST return late — since a buyer's ITC claim depends on your outward supply being reflected in the system, a delay on your side directly delays your buyer, even if your invoice itself was perfectly formatted.
Make a GST Invoice Free
The invoice generator has a GST mode: add your GSTIN, choose intra- or inter-state, and it splits CGST/SGST or applies IGST and totals it for you automatically — then download the finished PDF. Nothing you enter is uploaded anywhere. Learn the general fields every invoice needs (GST or not) in how to make an invoice, and see the full field checklist for a copy-paste-ready list.
Frequently Asked Questions
What is the GST invoice format?
A tax invoice with the supplier's and buyer's GSTIN, a unique number and date, the place of supply, HSN/SAC codes, taxable value, and the CGST/SGST or IGST breakdown — see the full mandatory-fields list above.
When do I charge CGST/SGST vs IGST?
CGST plus SGST applies to supplies within the same state; IGST applies to supplies across different states. The determining factor is the place of supply, not where your business happens to be registered.
Is GSTIN mandatory on an invoice?
The supplier's GSTIN is always mandatory. The buyer's GSTIN is required when the buyer is also GST-registered, so they can claim input tax credit against the invoice.
Can I create a GST invoice for free?
Yes — use the GST mode in the free invoice generator, which calculates the correct CGST/SGST or IGST split automatically based on the states you enter.
What's the difference between a tax invoice and a bill of supply?
A tax invoice is issued by GST-registered businesses charging GST; a bill of supply is issued by composition-scheme dealers or for exempt supplies, where GST isn't charged separately.
Can I edit a GST invoice after sending it?
No — issue a credit note or debit note instead, referencing the original invoice number, so your invoice sequence and audit trail stay intact rather than a silently altered original.
How do I correct a mistake on a GST invoice I've already sent?
Issue a credit note or debit note referencing the original invoice number — never edit or delete the original, since that breaks the audit trail GST compliance depends on.
Do small businesses below the GST threshold need to follow this format?
No — businesses not registered under GST issue regular invoices without GST fields. The tax invoice format above applies once you're GST-registered, whether by exceeding the threshold or registering voluntarily.
What happens if I get the place of supply wrong on an invoice?
You risk charging the wrong tax structure (CGST/SGST instead of IGST, or vice versa), which can complicate your buyer's input tax credit claim and your own GST return reconciliation — it's worth double-checking on every inter-state sale specifically.
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