# What Is an IRN (Invoice Reference Number) Under GST?

**Category:** GST | **Published:** 2026-06-25 | **Last reviewed:** 2026-06-25 | **Author:** Mrs. Swapna Patel

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.

> **Myth:** The IRN is just a serial number your billing software prints on the invoice.
>
> **Fact:** The IRN is a 64-character hash returned by the government [Invoice Registration Portal](https://einvoice1.gst.gov.in) under [Rule 48(4) of the CGST Rules](https://www.cbic.gov.in/htdocs-cbec/gst/cgst-rules-as-amended); 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](https://einvoice1.gst.gov.in) generates when a business reports an invoice for e-invoicing under [Rule 48(4)](https://www.cbic.gov.in/htdocs-cbec/gst/cgst-rules-as-amended). 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.

**[See when an invoice must carry an IRN and QR code](https://hrareceipt.in/atlas/e-invoicing-irn-5-crore-threshold)**

## 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](https://www.cbic.gov.in/htdocs-cbec/gst/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](/answers/e-invoicing-gst-5-crore-threshold-fy2026-27).

**[Generate a GST tax invoice in 60 seconds](https://hrareceipt.in/pakka-bill)**

## Primary sources

- [Rule 48(4), Central Goods and Services Tax Rules 2017 — CBIC](https://www.cbic.gov.in/htdocs-cbec/gst/cgst-rules-as-amended) — Mandatory e-invoicing and reporting of invoice particulars to the IRP.
- [GST e-invoice portal (IRP) — GSTN](https://einvoice1.gst.gov.in) — The 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)](https://einvoice6.gst.gov.in/content/revised-time-limit-for-e-invoice-reporting-for-businesses-with-aato-of-%E2%82%B910-crores-above/) — Time limit for reporting invoices to the IRP; applies to specified turnover slabs.

## Related

- [What is the IRP — the portal that returns the IRN](https://hrareceipt.in/answers/what-is-irp-invoice-registration-portal)
- [The Rs. 5 crore e-invoicing threshold for FY 2026-27](https://hrareceipt.in/answers/e-invoicing-gst-5-crore-threshold-fy2026-27)
- [GST tax invoice fields under Section 31 and Rule 46](https://hrareceipt.in/answers/gst-tax-invoice-fields-section-31-rule-46)
- [What is a pakka bill — the GST invoice that counts as valid](https://hrareceipt.in/answers/what-is-a-pakka-bill)

---

*Source: [What Is an IRN (Invoice Reference Number) Under GST?](https://hrareceipt.in/answers/what-is-an-irn-invoice-reference-number) — HRAReceipt.in*
*This Markdown mirror is published for AI-crawler ingestion. The canonical HTML page is the definitive version.*