By S&S Co. Advocates & Solicitors · Published 20 September 2026 · Informational content, not legal advice — see our disclaimer
Who Must E-Invoice
E-invoicing is mandatory for any GST-registered business whose aggregate annual turnover has exceeded Rs. 5 crore in any financial year since 2017-18. Once a business crosses this threshold even once, e-invoicing remains mandatory for all its GSTINs under that PAN going forward, even in years where turnover later falls below Rs. 5 crore — the obligation does not reverse with a later dip in revenue.
How IRN Generation Works
E-invoicing requires reporting the invoice, and any credit or debit notes, to a government-notified Invoice Registration Portal, which validates it and returns a unique Invoice Reference Number along with a QR code. An invoice without a valid IRN is not a valid tax invoice for GST purposes — a business cannot treat an unregistered invoice as compliant simply because it contains all the usual invoice details.
The Hard 30-Day Reporting Window
Since 1 April 2025, businesses with aggregate annual turnover of Rs. 10 crore or more face a hard 30-day reporting window: invoices, credit notes and debit notes older than 30 days from their date cannot be reported to the portal for IRN generation at all, effectively barring the document from ever becoming a valid e-invoice. Businesses with turnover between Rs. 5 crore and Rs. 10 crore must still generate e-invoices but are not yet subject to this hard 30-day stop as of the most recent reporting — though this threshold has historically been lowered progressively, and should be re-checked against the current GSTN advisory.
Why Missing the Window Hurts the Buyer, Not Just the Seller
Missing the 30-day window has a cascading effect: the buyer's input tax credit is put at risk because ITC claims are matched against valid e-invoice and IRN data flowing into GSTR-2B, so a late or missed IRN can mean the recipient effectively loses ITC on that transaction, even though the failure originated with the seller.
Practical Compliance Checklist
Businesses subject to e-invoicing should automate invoice-to-portal transmission close to the point of invoice generation, reconcile IRN-generation failures daily rather than at month-end, and build internal escalation for any invoice approaching the 25-27 day mark to avoid the 30-day cutoff entirely.
Frequently Asked Questions
At what turnover does e-invoicing become mandatory?
Once aggregate annual turnover exceeds Rs. 5 crore in any financial year since 2017-18. The obligation continues for all GSTINs under that PAN going forward, even if turnover later falls below Rs. 5 crore.
What is the 30-day rule?
Since 1 April 2025, businesses with turnover of Rs. 10 crore or more cannot report an invoice, credit note or debit note to the IRP for IRN generation if it is older than 30 days from its date — the document can never become a valid e-invoice after that.
How does a missed IRN affect the buyer?
ITC claims are matched against valid e-invoice/IRN data flowing into GSTR-2B, so a late or missed IRN on the seller's side can mean the buyer effectively loses input tax credit on that transaction.
References & Further Reading
This article references the following statutory provisions. Readers should always verify current rules, fees and timelines against the applicable statute and rules as amended, since these are revised from time to time.
- Central Goods and Services Tax Rules, 2017, e-invoicing provisions, as amended.
- GSTN advisories on the 30-day IRN reporting rule (effective 1 April 2025), current as of the date of reliance.