If your business is registered under GST in India, your invoices must follow specific rules. Missing fields or wrong tax calculations can lead to rejected input tax credits for your buyers and compliance issues for you. Here is what you need to create a GST-compliant invoice.
Who Needs to Issue GST Invoices
If your aggregate turnover exceeds ₹20 lakh (₹10 lakh for special category states) in a financial year, you must register under GST and issue tax invoices for taxable supplies. Below the threshold, registration is optional. Once registered, every taxable supply needs a proper tax invoice.
Mandatory Fields on a GST Invoice
GST law requires these fields. Missing any can invalidate the document:
- Supplier name, address, and GSTIN (15-digit)
- Invoice number (unique, sequential within financial year)
- Invoice date
- Recipient name, address, and GSTIN (for B2B)
- Place of supply (state name and code)
- HSN or SAC code for goods or services
- Description of goods or services
- Quantity and unit of measure
- Taxable value (before tax)
- Tax rate and amount (CGST, SGST, or IGST)
- Total invoice value
- Signature of supplier or authorized person
CGST + SGST vs. IGST
Intra-state supply (buyer and seller in same state): Split GST into CGST (Central) and SGST (State). For 18% GST, show 9% CGST and 9% SGST.
Inter-state supply (buyer and seller in different states): Charge IGST at the full rate. For 18% GST, show 18% IGST.
The place of supply determines which applies. Get it wrong and the tax calculation is invalid.
HSN and SAC Codes
HSN (Harmonized System of Nomenclature) codes classify goods. SAC (Services Accounting Code) codes classify services. They determine the applicable GST rate. Use the correct code for each item. Common services: SAC 998313 (IT design and development), SAC 998314 (IT infrastructure and network management).
Invoice Numbering Under GST
Numbers must be unique and sequential within a financial year. Gaps require explanation. Don't reuse numbers. Format is flexible (INV-001, 2026-001, etc.) as long as it is consistent.
Reverse Charge Mechanism Basics
Normally the supplier pays GST. Under reverse charge, the buyer pays. This applies to specific goods and services (e.g., some imports, certain supplies from unregistered persons). If reverse charge applies, the invoice must state "Tax payable under reverse charge."
Common Mistakes
- Wrong GSTIN. A single digit error prevents the buyer from claiming input tax credit.
- Missing place of supply. This determines CGST+SGST vs. IGST. Wrong place means wrong tax.
- Incorrect HSN/SAC. Wrong code can mean wrong rate and compliance issues.
- Late issuance. For goods, issue on or before removal. For services, within 30 days of supply.
Digital Tools for GST Invoicing
Manual GST invoices are error-prone. Software that handles mandatory fields, HSN/SAC codes, and tax calculations reduces mistakes. InvoiceBlitz offers a GST invoice generator with INR support and the fields you need for compliance. Create invoices that meet GST requirements without wrestling with spreadsheets.