What is a GST Invoice?
A GST invoice is a legal document that every registered business in India must issue when selling goods or services. It's not just a bill — it's the foundation of India's tax system. Without a proper GST invoice, your buyer can't claim Input Tax Credit (ITC), and you risk penalties during audits.
Whether you're a freelancer, shopkeeper, or startup — if your turnover exceeds Rs 40 lakh (Rs 20 lakh for services), you need to issue GST-compliant invoices.
Mandatory Fields in a GST Invoice
Every GST invoice MUST contain these 16 fields:
- Invoice number — unique, sequential, max 16 characters
- Invoice date
- Supplier name (your business name)
- Supplier GSTIN (15-digit GST number)
- Supplier address
- Buyer name
- Buyer GSTIN (if registered)
- Buyer address
- Place of supply (state — determines CGST/SGST vs IGST)
- HSN/SAC code — use our HSN Code Finder to look up the correct code
- Description of goods/services
- Quantity and unit
- Total value before tax
- Tax rate and amount (CGST + SGST or IGST)
- Total value after tax
- Signature (digital or physical)
CGST + SGST vs IGST — Which Tax to Charge?
This confuses most people. Here's the simple rule:
| Scenario | Tax Type | Example (18% GST) |
|---|---|---|
| Seller and buyer in same state | CGST 9% + SGST 9% | Mumbai → Pune |
| Seller and buyer in different states | IGST 18% | Mumbai → Delhi |
| Export or SEZ supply | IGST 0% (zero-rated) | Mumbai → Dubai |
The total tax amount is the same — only the split between central and state government changes. Our GST Invoice Generator handles this automatically based on the supplier and buyer state.
HSN/SAC Code Requirements
Since April 2021, HSN/SAC codes are mandatory on invoices based on turnover:
- Below Rs 1.5 crore — HSN code is optional
- Rs 1.5 crore to Rs 5 crore — 4-digit HSN code required
- Above Rs 5 crore — 6-digit HSN code required
Not sure which code applies to your product? Use our HSN & SAC Code Finder — search by product name and get the code with GST rate instantly.
Common GST Invoice Mistakes
- Wrong GSTIN — always verify buyer's GSTIN on the GST portal before invoicing
- Missing HSN code — mandatory for turnover above Rs 1.5 crore
- IGST on intra-state supply — should be CGST + SGST, not IGST
- Non-sequential invoice numbers — gaps in numbering trigger audit flags
- Amount in words missing — required for invoices above Rs 50,000
- No place of supply — this determines which tax type applies
Generate GST Invoices Instantly
Instead of formatting invoices manually in Excel or Word, use our free GST Invoice Generator:
- Auto-calculates CGST + SGST or IGST based on states
- Supports all tax slabs: 5%, 12%, 18%, 28%
- Multiple line items with HSN/SAC codes
- Amount in words (Indian numbering — lakhs, crores)
- Download as professional PDF
- 100% free, no signup, works in your browser