TL;DR: A GST invoice is a tax document required under India's Goods and Services Tax system. It must include your GSTIN, the recipient's GSTIN (for B2B), HSN or SAC codes, and a proper tax breakdown showing CGST, SGST, or IGST amounts. Non-compliant invoices can result in penalties and loss of input tax credit for your clients. Use a GST invoice generator to ensure compliance.
GST invoicing in India has specific format requirements set by law. This chapter covers exactly what fields your GST invoice needs, how to calculate and display taxes correctly, and how to avoid compliance issues.
Mandatory Fields on a GST Invoice
Under GST law, every tax invoice must include:
Supplier (your) details
- Business name
- GSTIN (15-digit GST Identification Number)
- Address
Recipient (client) details
- Client name and address
- Client GSTIN (required for B2B transactions over ₹2.5 lakh)
- State code and state name
Invoice specifics
- Invoice number (unique, sequential, max 16 characters)
- Invoice date
- Place of supply (determines CGST+SGST vs IGST)
Item details
- Description of goods or services
- HSN code (for goods) or SAC code (for services)
- Quantity and unit
- Taxable value (before tax)
- GST rate applicable
Tax breakdown
- Intra-state supply: CGST amount + SGST amount (e.g., 9% CGST + 9% SGST = 18% total)
- Inter-state supply: IGST amount (e.g., 18% IGST)
Totals
- Total taxable value
- Total tax amount
- Grand total (in figures and words)
CGST + SGST vs IGST
The tax split depends on where you and your client are located:
- Same state (e.g., Mumbai seller → Mumbai buyer): Split into CGST and SGST. If the rate is 18%, you charge 9% CGST + 9% SGST.
- Different states (e.g., Mumbai seller → Delhi buyer): Charge IGST at the full rate (18% IGST).
Getting this wrong means your client cannot claim input tax credit, which will cause problems for both of you.
HSN and SAC Codes
HSN (Harmonized System of Nomenclature) codes classify goods. SAC (Services Accounting Code) codes classify services. You need to include the correct code on every invoice:
- Businesses with turnover up to ₹5 crore: 4-digit HSN code
- Businesses with turnover above ₹5 crore: 6-digit HSN code
- Services: 6-digit SAC code
Common GST Invoice Mistakes
- Wrong GSTIN — Double-check your client's GSTIN before invoicing. An incorrect GSTIN means they cannot claim ITC.
- Missing place of supply — This determines whether you charge CGST+SGST or IGST.
- Wrong HSN/SAC code — Using the wrong code can lead to tax disputes.
- Calculations errors in tax split — CGST and SGST must be equal (both 9% for an 18% rate, not 10% + 8%).
Tools for GST Invoicing
Manually ensuring GST compliance on every invoice is error-prone. Our GST invoice generator handles the format, tax calculations, and HSN/SAC lookups automatically. For Indian businesses needing complete invoicing with GST compliance, see our invoice software for India guide. You can also create a basic invoice for free and add GST details manually.