What is a GST Invoice?
A GST invoice (also called a tax invoice) is a document issued by a registered supplier to the buyer at the time of sale. It serves as proof of supply and is essential for the buyer to claim Input Tax Credit (ITC). Under GST law, every registered person making a taxable supply must issue a tax invoice.
Mandatory Fields in a GST Invoice
As per Rule 46 of the CGST Rules, a tax invoice must contain the following details:
| Field | Description |
|---|---|
| Supplier Name and Address | Legal name and address of the registered supplier |
| Supplier GSTIN | 15-digit GST Identification Number |
| Invoice Number | Unique, sequential, max 16 characters |
| Invoice Date | Date of issue of the invoice |
| Recipient Name and Address | Name and address of the buyer |
| Recipient GSTIN | GSTIN if the buyer is registered |
| HSN/SAC Code | HSN for goods, SAC for services |
| Description of Goods/Services | Clear description of items supplied |
| Quantity and Unit | Quantity with unit of measurement |
| Taxable Value | Value before GST |
| GST Rate and Amount | CGST, SGST/UTGST, or IGST breakup |
| Total Invoice Value | Including tax amount in words |
| Place of Supply | State code where supply is delivered |
| Signature | Digital or manual signature of supplier |
Types of GST Invoices
- Tax Invoice – For taxable supplies of goods or services
- Bill of Supply – For exempt supplies or by composition dealers (no tax charged)
- Receipt Voucher – Issued when advance payment is received
- Debit Note – When taxable value or tax increases after original invoice
- Credit Note – When taxable value or tax decreases, or goods are returned
HSN Code Requirements on Invoices
The number of HSN digits required depends on your annual turnover:
- Up to ₹5 crore turnover: 4-digit HSN code
- Above ₹5 crore turnover: 6-digit HSN code
Invoice Series and Numbering Rules
GST invoices must follow sequential numbering with no gaps. You can use multiple series (e.g., INV/2025/001, SRV/2025/001) for different business verticals, but each series must be sequential. The invoice number cannot exceed 16 characters.
Time Limit for Issuing Invoices
- Goods: Before or at the time of removal/delivery
- Services: Within 30 days from the date of supply
- Continuous supply: Before the due date of payment or receipt of payment
Common Invoice Mistakes to Avoid
- Missing or incorrect GSTIN of the buyer
- Wrong HSN/SAC codes leading to ITC rejection
- Not mentioning place of supply (affects CGST/SGST vs IGST determination)
- Non-sequential invoice numbering
- Missing "reverse charge" declaration when applicable
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