What Is an IRN? The Invoice Reference Number, Explained
Priya Sharma
· Corporate Legal & Compliance Counsel· 3 min read
The Invoice Reference Number is what makes an e-invoice an e-invoice. It is not a number you assign; it is a hash the government portal computes and hands back, and its presence is what converts your document from a piece of paper into a registered tax invoice.
- ✓The IRN is a 64-character hash computed from supplier GSTIN, document type, document number and financial year.
- ✓It is generated by the Invoice Registration Portal, never by your own software.
- ✓An invoice requiring an IRN but lacking one is not a valid tax invoice.
- ✓The portal also returns a digitally signed QR code that must be printed on the invoice.
How the hash is built
The IRN is generated from four inputs: the supplier's GSTIN, the document type (INV, CRN or DBN), the document number, and the financial year in YYYY-YY format. Those are concatenated and hashed with SHA-256 to produce a 64-character string unique to that document.
Because the inputs include your own invoice number, the same invoice number cannot be registered twice in the same financial year. Attempting it returns a duplicate IRN error, which is the portal's way of enforcing the uniqueness Rule 46 already requires.
What the portal returns
A successful registration returns the IRN, an acknowledgement number and date, and a digitally signed QR code. The QR code embeds the supplier and recipient GSTINs, the invoice number and date, the invoice value, the number of line items, the HSN of the main item, and the IRN itself, all signed by the portal.
That signature is the point. Anyone scanning the QR code can verify the invoice was registered and has not been altered since, without contacting you at all.
What must be printed
The signed QR code must appear on the printed or PDF invoice. The IRN itself is commonly printed alongside it, and while the rules focus on the QR code, showing both is standard practice and helps recipients reconcile.
What you must not do is design your own QR code. The one you print has to be the signed payload the portal returned, because an unsigned code carries no verification value.
Cancellation and the 24-hour window
An IRN can be cancelled on the portal within twenty-four hours of generation, and only in full. Partial cancellation does not exist. After the window closes, the only route is a credit note, which itself carries an IRN.
A cancelled invoice number cannot be reused for a fresh IRN in the same financial year, because the hash inputs would be identical. The replacement invoice needs a new number.
Where the data goes next
Registration pushes the invoice data to the GST portal, where it pre-populates GSTR-1, and to the e-way bill system, where it can generate Part A automatically if transport details were included.
This is the quiet benefit of e-invoicing: the same payload serves three obligations. The cost is that errors propagate to all three, which is why validation before submission matters more than it used to.
Frequently asked questions
### Can I generate an IRN myself?
No. Only the Invoice Registration Portal can generate a valid IRN, because the digital signature on the returned payload is what gives it legal effect. Software that computes the hash locally is predicting the number, not registering the invoice.
### What happens if an invoice has no IRN?
Where e-invoicing applies, the document is not a valid tax invoice. Your customer's input tax credit on it is exposed, and you face penalties under Section 122 — ten thousand rupees per invoice for failure to issue, twenty-five thousand for an incorrect one.
### Can an IRN be cancelled?
Within twenty-four hours of generation, in full only. There is no partial cancellation and no amendment. After twenty-four hours the correction route is a credit note, and amendments to reported data happen in GSTR-1 rather than on the portal.
### Is the IRN the same as the invoice number?
No. Your invoice number is one of the four inputs used to compute the IRN, but the IRN itself is a 64-character hash returned by the portal. Both appear on the document, serving different purposes.
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Frequently Asked Questions
Can I generate an IRN myself?
No. Only the Invoice Registration Portal can generate a valid IRN, because the digital signature on the returned payload is what gives it legal effect. Software that computes the hash locally is predicting the number, not registering the invoice.
What happens if an invoice has no IRN?
Where e-invoicing applies, the document is not a valid tax invoice. Your customer's input tax credit on it is exposed, and you face penalties under Section 122 — ten thousand rupees per invoice for failure to issue, twenty-five thousand for an incorrect one.
Can an IRN be cancelled?
Within twenty-four hours of generation, in full only. There is no partial cancellation and no amendment. After twenty-four hours the correction route is a credit note, and amendments to reported data happen in GSTR-1 rather than on the portal.
Is the IRN the same as the invoice number?
No. Your invoice number is one of the four inputs used to compute the IRN, but the IRN itself is a 64-character hash returned by the portal. Both appear on the document, serving different purposes.
Priya Sharma
Corporate Legal & Compliance CounselSpecializing in commercial contract litigation, Section 138 NI Act recovery, commercial property leases, and MSMED Act compliance.