GST Invoicing Rules in 2026: Complete Guide for Indian Small Businesses

In India, issuing a valid GST tax invoice is legally mandatory under Section 31 of the Central Goods and Services Tax (CGST) Act. A compliant invoice ensures that your business collects tax legally and enables your B2B customers to claim Input Tax Credit (ITC) without department notices.

1. Mandatory 16 Fields on a GST Tax Invoice

According to GST Rule 46, every tax invoice issued by a registered taxpayer must contain the following 16 mandatory fields:

1. Supplier Name, Address, and GSTIN: Legal business name and registered store address.
2. Consecutive Serial Number: Unique alphanumeric sequence (max 16 characters).
3. Date of Invoice Issue: Date the bill was generated at the counter.
4. Recipient Details (B2B): Name, address, and GSTIN of the registered buyer.
5. Recipient Details (B2C > ₹50,000): Name, delivery address, state name, and state code.
6. HSN / SAC Code: 4-digit, 6-digit, or 8-digit classification code.
7. Description of Goods / Services: Clear specification of item sold.
8. Quantity & Unit of Measurement (UOM): Pcs, Kg, Litres, Box, etc.
9. Total Value of Supply: Base rate multiplied by quantity before discount.
10. Taxable Value: Value after deducting eligible commercial volume discounts.
11. Tax Rates: Separate rate percentages for CGST, SGST, IGST, and Cess.
12. Tax Amount: Calculated tax in INR.
13. Place of Supply (POS): Name of the State where delivery takes place.
14. Delivery Address: If different from the recipient's registered address.
15. Reverse Charge Mechanism (RCM): Whether tax is payable on reverse charge (Yes/No).
16. Authorized Signature / Digital QR: Merchant sign or verified QR code.

2. HSN Code Digit Requirements Based on Turnover

• Aggregate Turnover up to ₹5 Crores: Minimum 4-digit HSN code for all B2B invoices (optional for B2C).
• Aggregate Turnover exceeding ₹5 Crores: Mandatory 6-digit HSN code for all B2B and B2C transactions.
• Import / Export Transactions: Mandatory 8-digit international HSN code.

3. Difference Between Tax Invoice, Bill of Supply, and Cash Memo