GST Invoice Format: Required Fields, CGST/SGST vs IGST and HSN Codes
Everything a valid GST tax invoice must contain under the CGST Rules, how to apply CGST+SGST or IGST, HSN/SAC digit rules, and a free generator.
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A GST tax invoice isn't just a bill — it's the document your customer uses to claim input tax credit. If mandatory fields are missing or the tax type is wrong, their credit can be denied and the relationship suffers.
Mandatory fields on a tax invoice (Rule 46, CGST Rules)
- Supplier's name, address and GSTIN
- A unique, consecutive invoice number (max 16 characters) for the financial year
- Date of issue
- Recipient's name, address and GSTIN (if registered)
- For unregistered recipients with value over ₹50,000 — name, address and state
- HSN code for goods or SAC for services
- Description of goods or services
- Quantity and unit
- Total value and taxable value after discounts
- Rate and amount of CGST, SGST/UTGST or IGST, and cess
- Place of supply with state name (for inter-state supplies)
- Whether tax is payable on reverse charge
- Signature or digital signature of the supplier or authorised representative
The free GST Invoice Generator lays out all of these, calculates the tax split automatically and adds the amount in words.
CGST + SGST or IGST?
It depends on where the supplier is and the place of supply:
| Situation | Tax | Example at 18% |
|---|---|---|
| Same state (intra-state) | CGST + SGST (or UTGST) | 9% + 9% |
| Different states (inter-state) | IGST | 18% |
| Exports / SEZ supplies | IGST (zero-rated with LUT or with payment) | — |
The first two digits of a GSTIN are the state code (32 = Kerala, 27 = Maharashtra, 29 = Karnataka). In the generator, choosing the customer's state sets the place of supply and switches between CGST+SGST and IGST.
HSN and SAC digits
Based on aggregate turnover in the previous financial year:
| Turnover | HSN digits on B2B invoices |
|---|---|
| Up to ₹5 crore | 4 digits |
| Above ₹5 crore | 6 digits |
Check the current CBIC notifications, as these rules are revised from time to time.
Bill of supply
Composition dealers and suppliers of exempt goods issue a bill of supply instead of a tax invoice — no tax is charged. In the generator, set the title to "Bill of Supply" and the items to 0%.
E-invoicing
Businesses above the e-invoicing turnover threshold must report B2B invoices to the Invoice Registration Portal (IRP) and print the IRN and signed QR code. A generator like this can't create an IRN — you'll need e-invoicing-enabled software.
Amount in words
Not strictly mandatory, but standard practice in India — written in the Indian system (lakh, crore): "Rupees One Lakh Eighteen Thousand Only".
Beyond one-off invoices
Generators are fine for occasional invoices. When you need numbering that never duplicates, payment tracking, reminders, stock and reports, move to software — see Pyalm Books and Pyalm's business automation services.
This guide is general information, not tax advice — confirm requirements with your tax adviser.
Related free tools
GST Invoice Generator | GST Calculator | Invoice Generator | Receipt Generator | All free tools