How to Create a GST Invoice — Complete Step-by-Step Guide
Why Invoice Format Matters Legally
A GST invoice isn't just a bill — it's a legal document that determines whether your customer can claim Input Tax Credit, and whether you can defend your own tax position during an audit. An invoice missing mandatory fields, using the wrong tax split (CGST/SGST vs IGST), or citing an incorrect HSN/SAC code can lead to your customer's ITC claim being rejected and can attract penalties during GST scrutiny. Getting the format right from day one avoids costly disputes later.
All Mandatory Fields
| Field | Requirement |
|---|---|
| Invoice Number | Unique, sequential, max 16 characters |
| Invoice Date | Date of issue |
| Supplier GSTIN & Address | Mandatory on every invoice |
| Recipient GSTIN & Address | Mandatory for B2B; optional for B2C under ₹50,000 |
| HSN/SAC Code | Mandatory, digit-length depends on turnover |
| Description of Goods/Services | Clear item description |
| Quantity and Unit | For goods |
| Taxable Value | Value before tax |
| GST Rate and Amount | CGST+SGST or IGST, shown separately |
| Place of Supply | Mandatory for inter-state supply |
| Signature | Physical or digital signature of supplier |
Our free GST Invoice Generator pre-fills all these fields automatically and updates the live preview as you type — no missed fields, no manual tax calculation.
B2B vs B2C Differences
For Business-to-Business (B2B) invoices, the recipient's GSTIN is mandatory since they will use the invoice to claim ITC. For Business-to-Consumer (B2C) invoices, GSTIN is not required since consumers cannot claim ITC — only the name and address are needed, and for invoices under ₹50,000 even the address can be omitted for intra-state supply. This distinction also affects e-invoicing and reporting requirements in GSTR-1.
E-invoicing Applicability
E-invoicing — where invoices are electronically reported to the government's Invoice Registration Portal (IRP) and receive a unique IRN and QR code — is mandatory for businesses above a specified turnover threshold (currently ₹5 crore, though this is periodically revised downward). If e-invoicing applies to you, invoices generated outside the IRP system without an IRN are not treated as valid tax invoices, so check your applicability threshold each financial year.
5 Most Common Invoice Mistakes
- Wrong tax split: Charging CGST+SGST for an inter-state sale (or vice versa) instead of IGST — always check the buyer's state.
- Missing HSN/SAC code: Omitting or using an incorrect code, which can mismatch the applicable GST rate.
- Non-sequential invoice numbers: Skipping or duplicating invoice numbers, which raises red flags during audits.
- Incorrect place of supply: Especially relevant for services, where place of supply rules differ from the recipient's billing address.
- Rounding errors: Manually calculating GST and rounding inconsistently across line items instead of using a reliable calculator like GSTFlix's Standard GST Calculator.