# GST Invoice Format: Mandatory Fields, Rules, and Free Format Guide (2026)

> The exact GST invoice format required in India — all 16 mandatory fields, CGST/SGST vs IGST rules, HSN/SAC codes, and common format mistakes that invite notices.

Canonical: https://brightdesk.app/blog/gst-invoice-format-guide  
Last updated: 2026-07-22  
Author: Brightdesk Team  
Category: Finance

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:

1. **Supplier's name, address, and GSTIN**
2. **Invoice number** — consecutive serial, unique per financial year, max 16 characters (letters, numerals, hyphen/slash)
3. **Invoice date**
4. **Recipient's name, address, and GSTIN** (if registered)
5. For unregistered recipients on invoices above ₹50,000: name, address, and state
6. **HSN code** (goods) or **SAC code** (services) — digit requirements vary by turnover (see below)
7. **Description** of goods or services
8. **Quantity** and unit (for goods)
9. **Total value** of supply
10. **Taxable value** after discounts
11. **GST rate** — split as CGST + SGST/UTGST, or IGST
12. **Tax amount** — shown separately per tax head
13. **Place of supply** with state name (essential for inter-state supplies)
14. **Delivery address** if different from place of supply
15. **Reverse charge** indication, if applicable
16. **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](https://brightdesk.app/gst-invoice-generator) 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](https://brightdesk.app/blog/invoice-number-formats) 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

1. **Wrong tax split** (CGST/SGST vs IGST) — breaks the client's credit claim and your GSTR-1
2. **Missing place of supply** on inter-state invoices — technically invalid invoice
3. **Skipping or reusing serial numbers** — reconciliation nightmares and audit questions
4. **No SAC code** on service invoices above the turnover threshold
5. **Charging GST while on composition scheme** — outright violation
6. **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](https://brightdesk.app/blog/invoice-format-in-excel-vs-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 — in a [free Brightdesk account](https://brightdesk.app/gst-invoice-generator). Unlimited invoices, no card needed.

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