E-Invoicing Under GST: Complete Implementation Guide

If your business turnover has crossed ₹5 crore in any year since FY 2017-18, e-invoicing isn't optional — it's mandatory for every B2B invoice you issue. Here's exactly how it works and how to stay compliant.

What is E-Invoicing Under GST?

E-invoicing is a system where B2B invoices generated by your regular billing or accounting software must be reported to the government's Invoice Registration Portal (IRP) for real-time validation, before the invoice is considered legally valid for GST purposes. The IRP assigns a unique Invoice Reference Number (IRN) and a digitally signed QR code to each validated invoice.

Who Must Comply? (Turnover Threshold)

As of 2026, e-invoicing is mandatory for any GST-registered business whose aggregate annual turnover has exceeded ₹5 crore in any financial year since FY 2017-18 — even if the current year's turnover is lower, the obligation continues once you've crossed the threshold even once. Turnover is calculated on a PAN-wide, all-India basis.

Additionally, from April 1, 2025, businesses with an Annual Aggregate Turnover (AATO) of ₹10 crore or more must report their e-invoices to the IRP within 30 days of the invoice date — invoices reported after this window are treated as invalid for Input Tax Credit purposes.

What Transactions Are Covered?

• B2B invoices — supplies to other GST-registered taxpayers
• B2G invoices — supplies to government departments and entities
• Export invoices, with or without payment of IGST
• Deemed exports (supplies to EOUs, EPCG license holders, etc.)
• Credit notes and debit notes issued against B2B/export invoices

B2C invoices (to unregistered consumers) are not covered under mandatory e-invoicing, though a separate Dynamic QR Code requirement applies to large B2C invoices in some cases.

Who is Exempt?

• Special Economic Zone (SEZ) units (note: SEZ developers are NOT exempt and must comply if they cross the threshold)
• Banking companies and insurance companies
• Goods Transport Agencies (GTA) supplying road transport services
• Passenger transportation services
• Cinema ticket suppliers

How E-Invoice Generation Works

1. Generate the invoice through your regular billing/ERP/accounting software, following the standardized e-invoice schema
2. Upload the invoice data (directly via API integration, or through a GST Suvidha Provider) to the Invoice Registration Portal (IRP)
3. The IRP validates the data and generates a unique 64-character IRN, along with a digitally signed QR code
4. The signed invoice with IRN and QR code is sent back to you — this is the valid e-invoice you share with your buyer
5. Relevant invoice data automatically flows into your GSTR-1, reducing manual reconciliation work

What Happens If You Don't Comply?

• An invoice without a valid IRN is treated as invalid under GST law — essentially as if no invoice was issued at all
• Your buyer cannot claim Input Tax Credit on an invoice without a valid IRN, which can seriously damage business relationships
• Penalty under Section 122 of the CGST Act: ₹10,000 or the tax amount involved, whichever is higher, for each non-compliant invoice
• Repeated non-compliance can also trigger scrutiny of your GST returns