GSTR-1A Explained: Fix GSTR-1 Mistakes Before You File GSTR-3B (2026)

What is GSTR-1A?

GSTR-1A is an optional return that lets a supplier add missed invoices or correct details already reported in GSTR-1 for the same tax period. It was introduced by Notification 12/2024–Central Tax (Rule 59(4A)) and is available from the July 2024 tax period.

Before GSTR-1A existed, a mistake in GSTR-1 could only be corrected in the next month's GSTR-1 (Table 9A/9C). That meant a wrong liability went into GSTR-3B for the current month. GSTR-1A closes that gap: you fix the error before GSTR-3B is filed.

When can you file it?

• Opens: after you file GSTR-1 for the period.
• Closes: when you file GSTR-3B for that same period.
• How many times: once per tax period.

So the window is the gap between your GSTR-1 (11th) and GSTR-3B (20th) for a monthly filer.

Why GSTR-1A matters more since July 2025

From the July 2025 tax period, the tax liability that GSTR-3B auto-fills from GSTR-1, GSTR-1A and IFF (Table 3.1 and 3.2) is not editable in GSTR-3B. If GSTR-1 has a wrong figure, you can no longer just type the right one in GSTR-3B. The correction has to go through GSTR-1A first; GSTR-3B then picks up the corrected values.

What can you change in GSTR-1A?

You can	Example
Add an invoice missed in GSTR-1	Invoice INV/0045 was issued on 28th but left out
Correct the taxable value or tax	₹1,20,000 typed as ₹12,000
Correct the buyer's GSTIN	Wrong GSTIN means the buyer can't see the invoice
Correct place of supply / tax type	IGST charged on an intra-State sale
Amend B2CL, exports, credit/debit notes	Export shown with payment instead of under LUT

The changes also reach the buyer: corrected B2B records appear in the recipient's GSTR-2A and in the Invoice Management System (IMS), where they can accept, reject or keep them pending.

How to file GSTR-1A — step by step

1. Login → Services → Returns → Returns Dashboard, choose the financial year and period.
2. On the GSTR-1/IFF tile, open GSTR-1A (shown only after GSTR-1 is filed and before GSTR-3B).
3. Open the table you need (e.g. 4A B2B), click Add Record for a missed invoice or Amend on an existing one.
4. Save, then Generate Summary and check the totals.
5. File with DSC or EVC.
6. Open GSTR-3B — Table 3.1 now shows the corrected liability.

GSTR-1A vs amendment in the next GSTR-1

	GSTR-1A	Table 9A/9C in a later GSTR-1
Period	Same month, before GSTR-3B	Any later month (till 30 Nov of next FY)
Effect on GSTR-3B	Corrects this month's liability	Adjusts the later month's liability
Interest	None if paid on time with GSTR-3B	Interest if tax was short-paid earlier

Common mistakes

• Filing GSTR-3B first. Once GSTR-3B is filed, GSTR-1A for that month is gone — the fix moves to next month's GSTR-1.
• Assuming GSTR-3B can be edited. From July 2025, the outward liability in GSTR-3B is locked to GSTR-1/1A.
• Forgetting the buyer. A wrong GSTIN fixed late means your buyer's ITC is delayed.

Practise it safely

On IndIaTaxSim you file GSTR-1, spot a mistake, correct it in GSTR-1A and then watch GSTR-3B pick up the corrected figure — on a copy of the portal, with no real data at stake. The GST Portal Walkthrough covers it in Module 13.