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A GST invoice isn't just a bill — it's a legal document that determines your client's input tax credit and your compliance record. The format is prescribed by the GST rules, and getting it wrong has real consequences: rejected credits for your clients, penalties for you, and painful reconciliation at return-filing time. Here's the complete format, explained field by field.
The 16 Mandatory Fields
Per Rule 46 of the CGST Rules, a tax invoice must contain:
- Supplier's name, address, and GSTIN
- Invoice number — consecutive serial, unique per financial year, max 16 characters (letters, numerals, hyphen/slash)
- Invoice date
- Recipient's name, address, and GSTIN (if registered)
- For unregistered recipients on invoices above ₹50,000: name, address, and state
- HSN code (goods) or SAC code (services) — digit requirements vary by turnover (see below)
- Description of goods or services
- Quantity and unit (for goods)
- Total value of supply
- Taxable value after discounts
- GST rate — split as CGST + SGST/UTGST, or IGST
- Tax amount — shown separately per tax head
- Place of supply with state name (essential for inter-state supplies)
- Delivery address if different from place of supply
- Reverse charge indication, if applicable
- Signature or digital signature of the supplier or authorized representative
CGST + SGST or IGST? The One Rule
The most common format error is using the wrong tax split:
- Same state (your GSTIN state = place of supply): split the rate as CGST + SGST. An 18% service = 9% CGST + 9% SGST.
- Different states: charge IGST at the full rate (18% IGST).
Example: a Mumbai makeup artist bills a Mumbai bride → CGST 9% + SGST 9%. The same artist travels to a Goa destination wedding → the place of supply moves, and it's IGST 18%. Software that derives the split from both states automatically removes this error entirely.
HSN/SAC Digit Requirements
How many HSN/SAC digits you must print depends on your previous year's turnover:
| Aggregate turnover | HSN/SAC digits required |
|---|---|
| Up to ₹5 crore (B2B) | 4 digits |
| Above ₹5 crore | 6 digits |
| Up to ₹5 crore (B2C) | Optional |
Common SAC codes for service professionals: photography/videography services 998387, beauty and grooming 999721, event management 998596, catering 996334.
Invoice Numbering Rules
Your serial must be consecutive and unique within the financial year. A clean, compliant pattern: INV-2026-27-0001 (year-scoped, sequential). You may run multiple series (e.g., one per branch), but each must be internally consecutive. Random or repeated numbers are audit flags — see our invoice numbering guide for systems that scale.
Time Limits: When You Must Issue
- Services: within 30 days of providing the service (45 days for banking/insurance)
- Goods: on or before delivery/removal
- Advances: a receipt voucher at the time of receiving an advance; the tax invoice follows on supply
For wedding professionals collecting advances months before events, that receipt-voucher step is the most-missed compliance detail.
Copies, Bill of Supply, and Small-Invoice Relaxations
- Services require two copies (original for recipient, duplicate for supplier); goods require three (extra for transporter)
- Composition scheme dealers and suppliers of exempt goods issue a Bill of Supply instead — no tax shown, marked "composition taxable person, not eligible to collect tax"
- For B2C supplies under ₹200, a consolidated daily invoice is permitted
Common Format Mistakes That Cause Real Problems
- Wrong tax split (CGST/SGST vs IGST) — breaks the client's credit claim and your GSTR-1
- Missing place of supply on inter-state invoices — technically invalid invoice
- Skipping or reusing serial numbers — reconciliation nightmares and audit questions
- No SAC code on service invoices above the turnover threshold
- Charging GST while on composition scheme — outright violation
- Issuing tax invoices for advances instead of receipt vouchers — double-counting risk at filing
Excel Template or Software?
A well-built Excel format can be compliant — but it can't validate state-based tax splits, enforce serial continuity, or keep pace when you're issuing advance receipts and balance invoices across a busy season. That comparison is covered honestly in Excel vs invoicing software; the short version is that format errors are exactly the kind of mistake software eliminates by construction.
Generate a fully compliant GST invoice in under two minutes — correct tax split, SAC codes, and numbering included — with the free GST invoice generator. No signup required to try it.