GST Invoice Format in India: What a Valid Tax Invoice Must Include

If you are GST-registered in India, the invoice you send is not just a bill — it is a legal document. Get a field wrong and your client's accountant may bounce it, or worse, your input tax credit chain breaks. This guide walks through exactly what a valid GST tax invoice needs, in plain language.

Not legal advice. GST rules change and edge cases exist. Confirm specifics for your situation with a qualified Chartered Accountant.

What counts as a "tax invoice"

Under the CGST Rules, a registered supplier must issue a tax invoice for taxable supplies of goods or services. For services, it should be issued within 30 days of providing the service. A tax invoice is what lets your customer claim input tax credit (ITC) — so getting it right is doing your client a favour, not just satisfying a rule.

If you are not registered, or you supply exempt goods, you issue a bill of supply instead — which does not show tax.

The mandatory fields

A compliant GST tax invoice must carry all of the following:

1. 1.Your name, address, and GSTIN
2. 2.A consecutive invoice number (unique for the financial year — more on this below)
3. 3.The date of issue
4. 4.Customer name, address, and their GSTIN (if they are registered)
5. 5.Place of supply and state code — this is what decides CGST/SGST vs IGST
6. 6.HSN code (goods) or SAC code (services) for each line
7. 7.Description, quantity, and taxable value of each item
8. 8.Tax rate and tax amount, split into CGST + SGST/UTGST, or IGST
9. 9.Whether tax is payable on reverse charge
10. 10.Signature or digital signature of the supplier

Miss the GSTIN, the place of supply, or the SAC/HSN and you no longer have a valid tax invoice.

CGST + SGST vs IGST: the one rule that trips everyone

This is the single most common mistake. The split depends on place of supply, not on where you feel the client is:

• Intra-state (your state = place of supply): charge CGST + SGST, each at half the rate. A client in your own state at 18% means 9% CGST + 9% SGST.
• Inter-state (place of supply is a different state, or the customer is outside India): charge IGST at the full rate — 18% in one line.

For services, place of supply is usually the location of the recipient when they are registered. For exports of services, place of supply is outside India — which opens the door to zero-rating (covered in a separate post).

Invoice numbering: the rule people break without noticing

Your invoice numbers must be a consecutive series, unique within a financial year, and no more than 16 characters (letters, numbers, and / or - only). Practically:

• Do not reset your counter mid-year, and do not skip numbers.
• Do not reuse a number, even for a cancelled invoice — cancel and move on.
• A prefix is fine: 24-25/INV/001, INV-0001. Just keep it consistent and gapless.

Gaps and duplicates are exactly what a GST audit looks for, because they suggest invoices were deleted.

A minimal worked example

Say you are a designer in Gujarat billing a company in Maharashtra ₹50,000 for a design service at 18% GST. Because the states differ, it is inter-state → IGST:

If that same client were in Gujarat, you would instead show CGST ₹4,500 + SGST ₹4,500 — the total is identical, but the split is legally different.

Common mistakes that get invoices rejected

• Wrong tax split — charging CGST/SGST on an inter-state supply (or vice versa).
• Missing SAC/HSN — a blank code column.
• No place of supply — especially on export invoices.
• Broken numbering — gaps, resets, or duplicates.
• Editing a sent invoice — once issued and reported, correct it with a credit/debit note, not by silently editing.

Let the tool handle the split

The reason these mistakes are common is that they are easy to make by hand in a spreadsheet or Word template. A billing tool that knows your state and your client's place of supply can pick CGST/SGST vs IGST for you, keep numbering gapless, and never let a SAC field go blank.

That is exactly why we built Mavoin — GST-correct tax invoices without an accountant-grade ERP. If you invoice Indian clients and want the compliance handled quietly in the background, start a 30-day trial.