GST Invoice Format: All Mandatory Fields & Rules (2026)

A GST-compliant invoice isn't optional — it's a legal requirement under Section 31 of the CGST Act. Without a proper invoice, your buyer can't claim ITC, and you can face penalties up to ₹25,000 per invoice.

This guide covers all mandatory fields required under Rule 46, invoice numbering rules, e-invoicing requirements, and the different types of invoices (tax invoice, bill of supply, debit note, credit note).

Mandatory Fields in a GST Tax Invoice (Rule 46)

1. Name, address, and GSTIN of the supplier
2. Invoice number — consecutive, max 16 characters, unique per FY
3. Date of issue
4. Name, address, and GSTIN of the recipient (if registered)
5. Name and address of recipient (if unregistered, value > ₹50,000)
6. HSN code — 4 digits (turnover ≤ ₹5 Cr) or 6 digits (turnover > ₹5 Cr)
7. Description of goods or services
8. Quantity and unit of measurement (for goods)
9. Total value of supply (before tax)
10. Taxable value (after discounts)
11. Rate of tax — CGST, SGST/UTGST, or IGST (with amount for each)
12. Place of supply (with state code) for inter-state
13. Delivery address (if different from billing address)
14. Whether tax is payable on reverse charge
15. Signature or digital signature of supplier (or authorized representative)

Invoice Numbering Rules

• Must be sequential (no gaps, no duplicates)
• Maximum 16 characters
• Can contain alphabets, numerals, dash (-), and slash (/)
• Can have multiple series (one per branch, one per state registration)
• New series allowed at start of each financial year
• Examples: INV/2026-27/0001, MH-B2B-000456

Types of GST Documents

E-Invoicing Requirements

E-invoicing is mandatory for businesses with aggregate turnover exceeding:

• ₹5 crore — from August 1, 2023 onwards
• Previously: ₹10 Cr (Oct 2022), ₹20 Cr (Apr 2022), ₹50 Cr (Apr 2021), ₹100 Cr (Jan 2021), ₹500 Cr (Oct 2020)

E-Invoice Process

1. Generate invoice in your billing system with all mandatory fields
2. Upload JSON to Invoice Registration Portal (IRP) within 30 days
3. IRP validates and returns IRN (Invoice Reference Number) + QR code + digital signature
4. Share the signed invoice (with QR) with the buyer
5. IRN-enabled invoices auto-populate GSTR-1 (no manual upload needed)

E-Invoice Exemptions

• Banking and insurance companies
• Financial institutions and NBFCs
• GTA (goods transport agencies)
• Passenger transportation services
• SEZ units (for supplies to DTA)

Time of Issue

Common Invoice Mistakes

1. Wrong place of supply: Causes IGST vs CGST+SGST errors. Place of supply determines which state gets the tax revenue.
2. Missing HSN code: Mandatory since April 2021. Penalties apply for non-compliance.
3. Non-sequential numbers: Gaps or duplicates can trigger scrutiny during audit.
4. No reverse charge mention: If RCM applies, must be stated on invoice.
5. Invoice number > 16 chars: The e-invoicing system rejects numbers exceeding 16 characters.
6. Rounding errors: Tax amounts should be rounded to 2 decimal places per line item.

Penalties for Non-Compliance

• Not issuing invoice: ₹25,000 per invoice (Section 122(1)(i))
• Wrong invoice: ₹25,000 per invoice (Section 122(1)(ii))
• Not generating e-invoice (when applicable): ₹25,000 + invoice treated as invalid for buyer's ITC
• Fraudulent invoice (without supply): 100% penalty on tax amount + criminal prosecution possible