GST · 25 June 2026
What Is an IRN (Invoice Reference Number) Under GST?
The Invoice Reference Number (IRN) is a unique 64-character code the Invoice Registration Portal (IRP) returns when a business reports a B2B invoice for e-invoicing under Rule 48(4) of the CGST Rules. It is what makes an e-invoice valid: an invoice that should carry an IRN but does not is not a legal document for input tax credit. E-invoicing currently applies to businesses with aggregate turnover above Rs. 5 crore, and a separate 30-day reporting deadline applies to larger taxpayers.
By Mrs. Swapna Patel
Last reviewed
25 June 2026
In this section
Answers
- What Is an IRN (Invoice Reference Number) Under GST?
- What Is a Pakka Bill? The GST Invoice That Counts as Valid
- What Is a Kaccha Bill? Why the Rough Slip Has No GST Standing
- Why Move From a Kaccha Bill to a Pakka Bill?
- How to Upgrade From a Kaccha Bill to a Pakka Bill (GST Invoice)
- 5 GST Invoice Mistakes That Trigger a Tax Notice (And How to Fix Them)
- 7 Fields Every Skilled Professional Must Put on a GST Invoice: Rule 46 Checklist
- What Makes a GST Invoice Legally Binding — And Why Clients Pay Faster When It Is
- What Is a Bill of Supply? The GST Document Without Tax
- What Is Input Tax Credit (ITC) Under GST?
The IRN is just a serial number your billing software prints on the invoice.
The IRN is a 64-character hash returned by the government Invoice Registration Portal under Rule 48(4) of the CGST Rules; your software cannot generate it, only the portal can.
What is an IRN?
Short answer
The IRN is a unique 64-character code the Invoice Registration Portal generates when a business reports an invoice for e-invoicing under Rule 48(4). It is the proof the invoice was registered with the government before it reached the buyer.
Under e-invoicing, a tax invoice is not finished when you print it. You upload its details to the IRP, which validates them and returns the IRN plus a signed QR code. Only then is the invoice legally complete. The IRN is a hash, not a serial number you choose; it is derived from your GSTIN, the invoice number, and the financial year.
Who has to generate an IRN?
Short answer
Businesses whose aggregate turnover crosses the e-invoicing threshold, currently Rs. 5 crore, must report B2B invoices to the IRP and obtain an IRN. (The threshold has been lowered in stages; confirm the limit in force for your year.)
- The threshold is based on aggregate annual turnover in any financial year from 2017-18 onward, not on a single year's sales.
- It applies to B2B supplies, exports, and credit/debit notes. Most B2C invoices are outside e-invoicing.
- Below the threshold, e-invoicing and the IRN are not required; a normal tax invoice under Rule 46 is enough.
Is there a deadline to generate the IRN?
Short answer
Yes. A 30-day limit to report an invoice to the IRP applies to larger taxpayers, with aggregate turnover of Rs. 10 crore or more, effective 1 April 2025 per the GSTN advisory. Miss it and the IRP rejects the invoice.
- This 30-day window is separate from the Rs. 5 crore threshold that decides whether you do e-invoicing at all.
- An invoice the IRP rejects for late reporting cannot carry a valid IRN, so the buyer's input tax credit on it is at risk.
- The turnover slab the 30-day rule applies to has been tightened over time; check the current GSTN advisory before relying on a higher cut-off.
Why does the IRN matter to the buyer?
Short answer
Because an e-invoice without a valid IRN is not the document Section 16 of the CGST Act needs for input tax credit.
- For sellers in scope, only an IRN-carrying invoice is legally valid, so issuing one without an IRN is a defective invoice.
- The buyer should see the IRN and the signed QR code on the invoice before claiming credit on it.
- For the wider e-invoicing picture, see the Rs. 5 crore e-invoicing threshold.
References & related
Primary sources
- Rule 48(4), Central Goods and Services Tax Rules 2017 — CBICMandatory e-invoicing and reporting of invoice particulars to the IRP.
- GST e-invoice portal (IRP) — GSTNThe portal that generates the IRN, signed QR code, and acknowledgement.
- GSTN advisory on 30-day e-invoice reporting limit (AATO ₹10 crore and above, effective 1 April 2025)Time limit for reporting invoices to the IRP; applies to specified turnover slabs.
Last reviewed: 25 June 2026