All about Invoice Reference Number (IRN)

IRN, known as Invoice Reference Number, is a unique number allotted by Government to tag and identify every valid e-invoice generated in India, first implemented from 1st October 2020. The e-invoicing system has been introduced to create a standard for all e-invoices generated. In this article, we will be dealing with the following aspects about Invoice Reference Number (IRN) in an e-invoice.

Latest Update

4th April, 2025

With effect from June 1, 2025, IRP will treat invoice numbers as case-insensitive for IRN generation. All invoice numbers in any format will be converted to uppercase to avoid duplication and ensure consistency.

What is an Invoice Reference Number (IRN)?

The Invoice Reference Number (IRN) is a unique number (also known as hash) generated by the Invoice Registration Portal (IRP) using a hash generation algorithm, under the e-invoicing system. For every document such as an invoice or debit or credit note to be submitted on the Invoice Registration Portal, a 64 character invoice reference number shall be generated. This number shall be unique for every invoice raised in a financial year by a GSTIN in the entire GST system.

Further, every invoice being issued by supplier to his recipient must contain the IRN. The tax officers can verify the genuineness of the transaction using invoice reference number through the central portal as well as an offline app. It will, in turn, help them check the invoice even where internet may not be accessible.

What is the Hash Generation Algorithm in IRN?

A hash generation algorithm is a function that converts a message or a string consisting of characters (alphabets + numbers + certain special characters) into a series of numbers such that the resulting numbers cannot indicate the original message. The GSTN will prescribe this algorithm as part of the e-invoicing standard.  

Case Sensitivity IRN Generation GSTN Advisory

The GST Network (GSTN) has issued an advisory that, effective 1st June 2025, the e-Invoicing system will treat Invoice Reference Numbers (IRN) as case-insensitive. This means invoice or document numbers with different letter cases will no longer be considered distinct by the Invoice Reporting Portal (IRP).

To ensure consistency and avoid duplication, invoice numbers reported in any format (e.g., "abc", "ABC", or "Abc") would be automatically converted to uppercase before IRN generation. This change aligns with the treatment of invoice numbers in GSTR-1, which already treats them as case-insensitive.

What are the Parameters used to Generate Invoice Reference Number (IRN)?

IRN is generated by converting characters into numbers (also called ‘hash’) using a hash generation algorithm. This algorithm will be applied to the following three parameters:

• Supplier GSTIN
• Supplier’s document number. For example, invoice number
• The financial year in ‘YYYY-YY’ format. For example 2019-20.

When is the Invoice Reference Number (IRN) Generated?

The generation of the Invoice Reference Number (IRN) is mandatory at the time the seller issues an invoice, credit note, or debit note. The IRN system is now fully operational and applies to businesses across different turnover thresholds.

The invoices under the e-invoicing system will continue to be prepared using any software that a business entity uses to generate invoices. However, they will have to conform to the prescribed standard and parameters.

The entity can choose either of the following two options to generate IRN:

Option 1: Using the Excel offline tool.  

Option 2: Through API integration directly with the e-invoice portal/IRP or via GST Suvidha Provider.

For more details about how IRN is generated, read our article on How to generate IRN?

Note: In both cases, the IRP will perform a de-duplication check where the IRN so generated will be checked against the Central Registry of the GST System (containing all generated/uploaded IRN) to ensure that all IRN remain unique.

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