E-invoicing under GST: who must do it and what changes when you cross ₹5 crore

What is the e-invoicing threshold under GST?

As of October 2026, e-invoicing is mandatory for any GST-registered business whose aggregate annual turnover (AATO) has exceeded ₹5 crore in any financial year from 2017-18 onwards. The ₹5 crore limit has applied since 1 August 2023. Below it, the rule does not apply.

Three details decide whether the rule catches you, and owners often get each one wrong:

• AATO is counted on the PAN, not the GSTIN. If you hold registrations in two states under one PAN, the turnover of both counts towards the ₹5 crore.
• Any single year counts. You are not tested on this year alone. If you crossed ₹5 crore in any financial year since 2017-18, the rule applies to you.
• Once in, always in. A later year below ₹5 crore does not take you out. Treat the obligation as permanent once you have crossed.

When does the rule start to bite for a growing business?

The rule bites in the year after your turnover first crosses ₹5 crore. The test looks back at completed financial years, so a business that crosses during the year usually has the rest of that year to get ready.

Here is how it could look for Lakshmi Steel Furnitures, the fictional Coimbatore business used across these guides. Its turnover today is well below ₹5 crore, so the later years are a growth plan, not actual figures.

In 2026-27 the plan leaves the business ₹37,90,000 below the line. At its growth rate, that gap closes in one good year. That is the moment to start preparing, not the March when the accountant closes the books.

What are an IRN and a signed QR code?

An IRN, or invoice reference number, is a unique number the government's Invoice Registration Portal assigns to each B2B invoice you report to it. You still raise the invoice in your own system with your own number. The portal checks it, gives it an IRN and signs it.

• Your invoice number stays yours, in your own series, up to 16 characters and unique within the financial year.
• The IRN is a long unique reference generated by the portal. It proves the invoice was registered.
• The signed QR code carries the key invoice details and the IRN. It goes on the printed or PDF invoice you send the buyer.
• The signed JSON is the portal's digitally signed copy of the invoice. The portal generally passes the details on to your GSTR-1.

Generally, an invoice that needed an IRN and did not get one is not treated as a valid tax invoice, and your buyer's input credit can depend on it. Dealers and corporate buyers tend to notice quickly.

Which invoices are covered and which are not?

E-invoicing generally covers documents you issue to registered buyers: B2B tax invoices, credit notes and debit notes, plus exports. Sales to consumers are outside it.

Some taxpayers are exempt whatever their turnover. These include SEZ units and certain sectors such as banks, insurers, goods transport agencies and passenger transport services. The exact list sits in the notifications on the CBIC site, so check it there if your business could fall into one of them.

Is there a deadline for reporting an invoice to the portal?

Yes, for larger taxpayers. As of the date of this guide, larger taxpayers must report an invoice to the portal within 30 days of the invoice date, or the portal may refuse to issue an IRN for it.

The turnover above which the 30-day window applies has been changed before, so check the current figure on the e-invoice portal rather than relying on a number in a blog post. A business just over ₹5 crore should still report on the day of the invoice. A late IRN means a buyer waiting on input credit and a GSTR-1 that does not match.

What should a small business prepare a year before crossing ₹5 crore?

Prepare your master data and your numbering, because the portal rejects invoices with bad data, not businesses with bad intentions. Common causes of rejection are a wrong GSTIN, a missing HSN or a reused number.

• Every B2B customer has a correct GSTIN, checked once against the GST portal, with the state that matches it
• Every product carries an HSN code at the right length (6 digits once AATO is above ₹5 crore)
• Every service carries a SAC code
• One clear invoice series per financial year, never reused and never edited after it is issued
• Credit notes and debit notes go through their own series and reference the original invoice
• Customer addresses, pin codes and place of supply are filled, not left blank
• Unit of measure on each product matches a standard unit, not a free-text abbreviation
• Someone is named to run the portal step each day and to keep the signed copies

The HSN code guide covers the digit rule in detail, and the place of supply guide covers why the buyer's state matters. Both checks pay off well before e-invoicing, because the same data feeds GSTR-1.

Does SimpleERP generate the IRN for you?

The workaround uses the e-invoice portal's own tools. The work SimpleERP does is making sure the invoice data is right before it reaches the portal, and keeping the signed copy with the record afterwards.

1. 1

   Post the invoice in SimpleERP

   The invoice takes its number from the fiscal-year series, such as INV-2026-27-0118, with the customer's GSTIN, the HSN on every line and CGST and SGST or IGST worked out from the place of supply.

2. 2

   Prepare the invoice on the portal's tools

   Use the free offline or bulk generation utility from the e-invoice portal. Enter the invoice details from the posted invoice and its HSN lines.

3. 3

   Upload and get the IRN

   Upload on the portal. It validates the data and returns the IRN, the acknowledgement number and the signed QR code.

4. 4

   Send the buyer the signed copy

   Print or share the invoice that carries the IRN and QR code, as produced from the portal's output.

5. 5

   Attach the signed copy to the invoice in SimpleERP

   Upload the signed PDF as a file on the sales invoice, so anyone opening the record later sees the IRN proof beside it.

This is manual work for every B2B invoice. At five to ten invoices a day it is manageable for one person. Well beyond that, talk to your accountant about a GST Suvidha Provider as well.

How does SimpleERP keep invoices ready for the portal?

SimpleERP keeps the fields the portal needs on every invoice, from the moment it is made. Fixing a GSTIN in the customer record once is far cheaper than fixing a rejected upload every week.

• Place of supply is derived from the GSTIN, so CGST and SGST or IGST follow the buyer's state without anyone choosing it.
• HSN or SAC sits on the product and flows to every invoice line, editable on the line when needed. The HSN summary report rolls them up.
• Numbering is fiscal-year based, INV-2026-27-0001, 16 characters, so a number is never reused within the year.
• Posted invoices cannot be edited. A mistake is corrected with a credit note or a cancellation that reverses the entry.
• The sales register lists every invoice with its tax split, ready to check against GSTR-1.

See the GST billing software page for the full invoice flow, and the GST billing guide for how e-invoicing fits with the rest of your GST work.