GSTR-1A: Correcting GSTR-1 Before GSTR-3B

GSTR-1A sits in a narrow gap most filers never used to think about: the days between filing GSTR-1 and filing GSTR-3B for the same period. For years that gap did not matter much, because GSTR-3B let you type over whatever number GSTR-1 produced. Now that Table 3 of GSTR-3B is auto-populated and locked from your own GSTR-1 and GSTR-1A, that gap is the only place left to fix an outward-supply mistake before it becomes your tax liability for the month. This post covers what GSTR-1A actually lets you change, how long the window stays open, and how it differs from correcting the same mistake later through an amendment table in a future GSTR-1.

What GSTR-1A is

GSTR-1A was introduced under Rule 59(1) of the CGST Rules, effective from the July 2024 tax period. It is a form a registered supplier can use, after filing GSTR-1 for a period, to add details of an outward supply that GSTR-1 missed, or to amend details already reported in that same GSTR-1 — before GSTR-3B for that period is filed. It does not replace GSTR-1, and it is not compulsory: if nothing in GSTR-1 needs fixing, there is nothing to file.

The closest way to think about it is a correction pass on the same month's return, rather than a separate filing cycle. For the underlying return it corrects, see the GSTR-1 filing guide; for the return it feeds into, see the GSTR-3B filing guide. For where GSTR-1A sits among the rest of the return set, see the list of GST returns.

Why it matters more since the auto-lock

Before GSTR-3B's outward-liability tables were locked, a GSTR-1 mistake was rarely urgent. You filed GSTR-1 with a typo, and Table 3 of GSTR-3B was a free-text field, so you simply typed the correct figure and paid the right tax. The two returns quietly disagreed, and that disagreement was usually cleaned up later, or flagged by a departmental notice.

That is no longer how it works. As covered in how GSTR-3B auto-locks from GSTR-1, the outward supply tables in GSTR-3B are now computed from GSTR-1, IFF and GSTR-1A for the period and presented as a value you cannot override — a change that applies from the July 2025 tax period onward. If GSTR-1 for a period understates or overstates your outward supplies, GSTR-3B for that period inherits the error unless you correct it first. GSTR-1A is that correction route, and it only works before GSTR-3B is filed.

The filing window

GSTR-1A opens once GSTR-1 (or IFF, for a QRMP filer's first two months) has been filed for the period, and it closes the moment GSTR-3B for that same period is filed. There is no separate due date printed on a calendar the way there is for GSTR-1 or GSTR-3B — the window is defined entirely by those two filing events.

That makes the practical deadline whatever you set it to be by choosing when to file GSTR-3B. File GSTR-3B the same day as GSTR-1 and you leave almost no room to catch an error. Build in a review step between the two filings and you have days to work with, bounded only by GSTR-3B's own statutory due date.

What you can and cannot change

GSTR-1A follows the same table structure as GSTR-1, so most of what you can add or correct maps directly onto GSTR-1's own sections.

Where the line falls on edge cases — a partially corrected invoice, a note issued against a pre-GST-1A invoice — is exactly the kind of detail that shifts between advisories. Confirm anything unusual against the current help content on gst.gov.in before filing.

One filing per period

GSTR-1A can be filed only once for a given tax period. That makes it worth treating as a single consolidated correction rather than a running edit log: review the auto-populated GSTR-3B, list every discrepancy against GSTR-1, and put all of them into one GSTR-1A filing before submitting it.

GSTR-1A under QRMP

Quarterly filers under QRMP get the same mechanism applied to the quarter. The first two months of a quarter go up through IFF, the whole quarter is consolidated in the quarterly GSTR-1, and GSTR-1A for that quarter opens after the quarterly GSTR-1 is filed and closes once the quarterly GSTR-3B is filed.

That gives a QRMP filer one correction window per quarter rather than per month, covering the whole quarter's outward supplies at once. It is worth reviewing the quarter's auto-populated GSTR-3B carefully before filing it, since there is no monthly GSTR-1A checkpoint to fall back on in between.

GSTR-1A versus an amendment in a later GSTR-1

GSTR-1 has always had its own amendment tables — B2BA for amended B2B invoices, B2CA for B2C, CDNA for credit and debit notes — used in a later period's GSTR-1 to correct an earlier period's reporting. That route still exists and does not disappear because of GSTR-1A. The two solve different timing problems.

In short: catch it before GSTR-3B, use GSTR-1A. Catch it after, the amendment moves downstream and the interest clock has already been running since the original due date.

Step-by-step on the portal

The exact screens change occasionally, so treat this as the shape of the process rather than a literal walkthrough, and confirm against the live portal when you file.

1. File GSTR-1 (or IFF) for the period as usual.
2. Before filing GSTR-3B, open the auto-populated GSTR-3B and compare Table 3 against your books.
3. If a figure looks wrong, go to Returns Dashboard for the period and open GSTR-1A, which becomes available once GSTR-1 is filed.
4. Add any missed records, or amend the specific invoices, notes or summaries that need correcting, using the same table layout as GSTR-1.
5. Review the consolidated set of changes — remember only one GSTR-1A filing is allowed for the period.
6. File GSTR-1A with DSC or EVC, the same way you would file GSTR-1.
7. Re-check the auto-populated GSTR-3B, confirm the figures now match your books, and file GSTR-3B.

Because GSTR-1A can change what your recipients see in their next GSTR-2B, it is worth flagging a GSTR-1A correction to any affected customer, particularly if it changes an invoice value or a place of supply they have already relied on. For what happens on their side once IMS and GSTR-2B pick the change up, see how IMS and GSTR-2B interact and GSTR-2A versus GSTR-2B.

Before booking or amending a large invoice this way, confirming the counterparty's GSTIN and filing history reduces the chance you are correcting a record for a supplier or customer whose registration has since changed status. Our API returns registration details and GSTR filing history in a single call, at ₹0.50 per verification, falling to ₹0.40 once a purchase crosses 2,500 credits.

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