GST Invoice Calculator: How to Create GST-Compliant Invoices
The 5 Fields That Make or Break GST Compliance
A GST invoice isn’t just a bill — it’s a legal document that determines whether your buyer can claim Input Tax Credit (ITC). Missing or incorrect fields can lead to ITC rejection for your buyer and penalties for you. Every registered business must issue a GST-compliant invoice for taxable supplies.
Mandatory Invoice Fields
- GSTIN of the supplier (your registration number)
- Invoice number — unique, sequential, max 16 characters, format: ALPHA/NUM/SPECIAL-CHARS
- Date of issue
- GSTIN of recipient (if registered)
- HSN/SAC code — turnover above ₹5 crore must show 6-digit HSN; ₹1.5–5 crore: 4-digit
- Description of goods/services, quantity, unit, and value
- Tax breakup: CGST + SGST (intra-state) or IGST (inter-state) with rates
- Place of supply (determines whether CGST/SGST or IGST applies)
- Total invoice value
- Signature or digital signature of supplier
CGST/SGST vs IGST: Which Applies?
| Transaction Type | Tax | Example |
|---|---|---|
| Intra-state (seller and buyer in same state) | CGST + SGST (split equally) | Mumbai seller to Pune buyer: 9% CGST + 9% SGST = 18% total |
| Inter-state (different states) | IGST (full rate) | Mumbai seller to Delhi buyer: 18% IGST |
| Export | IGST at applicable rate (or 0% under LUT) | Mumbai seller to US client: 0% with LUT |
Use the GST calculator to compute the exact tax breakup for any amount and rate.
Common GST Rates
| Rate | Applies To |
|---|---|
| 5% | Transport, packaged food, economy hotel rooms |
| 12% | Processed food, business class air tickets, IT services to non-SEZ |
| 18% | Most services, electronics, telecom, software, consulting |
| 28% | Luxury goods, automobiles, tobacco, cement, AC restaurants |
Invoice Numbering Rules
- Must be unique and sequential within a financial year
- Maximum 16 characters including alphabets, numerals, hyphens, and slashes
- Must not start with 0
- Series can be reset at the start of each financial year
- Example format: INV/2025-26/0001
Common Compliance Mistakes
- Wrong place of supply: Charging CGST+SGST for an inter-state transaction (should be IGST)
- Missing HSN/SAC code: Mandatory for businesses above the turnover threshold
- Duplicate invoice numbers: Can lead to ITC complications for buyers and notices from GST department
- Late invoice issue: Must be issued at or before the time of supply