India GST E-Invoicing in 2026: AATO Threshold, IRP, HSN/SAC and the 30-Day Reporting Rule
India's GST e-invoicing applies to every business with annual aggregate turnover above ₹5 crore. Generate IRN, sign QR, report within 30 days. Here's the practical SME guide and how Hisabi fits in.
India's e-invoicing system has expanded from large corporates to SMEs in successive waves since 2020. Today, every business with annual aggregate turnover (AATO) above ₹5 crore must generate e-invoices for B2B, exports and SEZ supplies through the Invoice Registration Portal (IRP).
From 1 April 2025, businesses with AATO above ₹10 crore must report e-invoices on the IRP within 30 days of issuance. The window is short and unforgiving — late reporting blocks the recipient's input tax credit.
How e-invoicing works in India
You generate the invoice in your system, push it to one of the IRPs (NIC, ClearTax, GSP), and the IRP returns three artefacts: the Invoice Reference Number (IRN), a QR code, and the digitally signed JSON. You then deliver the invoice (with QR) to the buyer. The IRP also pushes the data to the GSTN portal for GSTR-1 auto-population and to the e-Way Bill portal where applicable.
Mandatory fields
- Supplier and recipient GSTIN (15 characters, validated against GSTN).
- Invoice number — unique per financial year, max 16 characters, alphanumeric.
- Date of issue and place of supply.
- Line items with HSN code (4 / 6 / 8 digits depending on turnover) for goods, or SAC code for services.
- Per-line CGST, SGST, IGST and cess as applicable.
- Total invoice value in INR.
- Reverse-charge flag where applicable.
- Shipping details for goods.
HSN and SAC codes
HSN (Harmonised System of Nomenclature) for goods, SAC (Services Accounting Code) for services. Required digit depth depends on turnover: 4 digits for AATO ≤ ₹5 crore, 6 digits above ₹5 crore. Wrong code, rejected IRN.
Retention
Section 36 of the CGST Act requires records to be retained for at least 72 months (6 years) from the due date of the annual return. The signed JSON returned by the IRP must be preserved in original form.
How Hisabi helps
Hisabi structures Indian invoices with GSTIN validation, HSN/SAC at the right digit depth for your turnover, and CGST/SGST/IGST splits per line item. IRP integration (NIC GSP) is on the 2027 roadmap; today, Hisabi exports a JSON payload that loads directly into popular IRPs.