What Is an IRN and Why E-Invoices Need One
Once e-invoicing applies to your business, every qualifying invoice needs an Invoice Reference Number, or IRN — and unlike an invoice number, this isn't something you choose or generate yourself.
What an IRN actually is
An IRN is a unique 64-character hash, generated by an Invoice Registration Portal (IRP) using a SHA-256 algorithm run against your GSTIN, your invoice number, the financial year, and the document type. Two invoices can never produce the same IRN — that's the point of using a cryptographic hash rather than a sequential number.
How it gets generated
The invoice isn't created on the government portal. It's created in your own invoicing software, converted to a standard JSON format, and submitted to the IRP. The IRP validates it, generates the IRN, digitally signs the invoice, and embeds a QR code — then hands all of that back to you to attach to the invoice you actually send your customer.
Why it matters beyond compliance
- An invoice without a valid IRN isn't a legally valid e-invoice — it doesn't matter how correct every other field is.
- Your customer's input tax credit is tied to it — the IRN is what confirms to the system that this specific transaction was actually reported, not just claimed.
- It can't be corrected after the fact — an IRN can only be cancelled within 24 hours of generation, never edited. See amending an e-invoice after it's generated for what's actually allowed once that window closes.
The QR code embedded alongside the IRN carries the core invoice details in a scannable, verifiable form — see QR codes on GST invoices explained for what it actually contains.