When can GSTR-1A be filed for October 2026?

For a monthly filer it opens on the later of the GSTR-1 due date, 11 November 2026, and the date GSTR-1 is actually filed, and stays open until GSTR-3B for October is filed (due 20 November 2026 for monthly filers). It has no separate due date.

Is there a late fee for GSTR-1A?

No. The form instructions in CBIC Notification No. 12/2024 – Central Tax describe GSTR-1A as an optional form without levy of late fees.

How many times can GSTR-1A be filed?

Only once for a tax period, even if GSTR-3B is not yet filed. A nil GSTR-1A is not available, and records saved but not filed in GSTR-1A stop GSTR-3B from being filed.

What cannot be corrected in GSTR-1A?

The recipient GSTIN cannot be amended in GSTR-1A, and records reported in earlier periods cannot be amended in the current GSTR-1A. Those go into a later GSTR-1 within the time limit in the law.

Why does GSTR-1A matter for Table 3.2 of GSTR-3B?

GSTN advised on 5 December 2025 that from the November 2025 tax period the auto-populated values in Table 3.2 of GSTR-3B are non-editable; corrections are made through GSTR-1A for the same period.

GSTR-1A for October 2026: a fix-before-GSTR-3B sheet for CA firms (window 11 to 20 November, Table 3.2 locked)

Updated 25 Oct 2026 · Disclosure: the white-label calendar linked below is an Unadhi product (₹999/year). This guide is for information only, not professional advice.

What you get: a finished Google Sheet layout with four tabs: "Fix list" (one row per wrong or missed record in a client's October 2026 GSTR-1, with a route formula that says GSTR-1A or next month's GSTR-1), "Window" (one row per client: GSTR-1 filed on, the date GSTR-1A opens, GSTR-3B due, GSTR-1A filed, and a status formula), "3.2 check" (inter-State supplies to unregistered persons, composition taxpayers and UIN holders by State, from the books against GSTR-3B Table 3.2) and "Open" (a FILTER of everything not yet fixed), plus a made-up example, a plan for 11 to 20 November and a WhatsApp message for clients.

Short answer (checked 25 Oct 2026): GSTR-1A is an optional form to add a missed record or amend a record in the same tax period's GSTR-1. For a monthly filer's October 2026 return it opens on the later of the GSTR-1 due date (11 November) and the date GSTR-1 is actually filed, and it closes the moment that client's October GSTR-3B is filed (due Friday 20 November 2026 for monthly filers). It has no separate due date and no late fee, it can be filed only once per period, and it cannot change the recipient's GSTIN. The corrected values flow into GSTR-3B. Since the November 2025 tax period, GSTN has made Table 3.2 of GSTR-3B non-editable, so GSTR-1A is the way to correct it before filing.

What the official sources say

Legal basis: CBIC Notification No. 12/2024 – Central Tax (10 July 2024) added a proviso to rule 59(1) of the CGST Rules: after furnishing GSTR-1 for a tax period but before filing GSTR-3B for that period, a person may, at their own option, amend or furnish additional outward-supply details in FORM GSTR-1A. New rule 59(4A) lists what it can contain: invoice-wise B2B supplies, inter-State B2C invoices above ₹1 lakh, consolidated B2C details, and debit and credit notes.
Window: the GST portal FAQ says GSTR-1A opens for a monthly filer on the later of the GSTR-1 due date (11th of the following month) and the actual GSTR-1 filing date, and stays open until GSTR-3B of the same period is filed. For quarterly filers it opens after the quarterly GSTR-1 (due 13th after the quarter) and can also amend IFF records of the first two months.
No due date, no late fee: the FAQ says there is no due date for GSTR-1A; the form instructions in the notification call it an optional form without levy of late fees.
Once only, no nil: GSTR-1A can be filed only once for a tax period, even if GSTR-3B is not yet filed. A nil GSTR-1A is not available. It is filed online or through a GSP.
Not after GSTR-3B: once GSTR-3B is filed for the period, GSTR-1A is closed; corrections then go into a later GSTR-1, within the time limit in the law.
Saved but not filed blocks GSTR-3B: if records are saved in GSTR-1A but it is not filed, the portal will not let GSTR-3B be filed until you file, delete or reset GSTR-1A.
What it cannot fix: the recipient's GSTIN cannot be amended in GSTR-1A, and records of earlier periods' GSTR-1 cannot be amended in the current GSTR-1A.
Table 3.2 locked: GSTN's advisory of 5 December 2025 says that from the November 2025 tax period the auto-populated values in Table 3.2 of GSTR-3B (inter-State supplies to unregistered persons, composition taxpayers and UIN holders) are non-editable and must be corrected through GSTR-1A for the same period. The portal's GSTR-3B user guide (checked today) still describes other auto-populated tables as editable with a red warning; GSTN's June 2025 advisory had announced locking auto-populated liability too, so check each client's GSTR-3B screen rather than relying on editing it there.

Tab "Fix list": one row per record to correct

Column	What to write
A. Client	Client name and GSTIN
B. Document	Invoice, debit note or credit note number and date (October 2026 only)
C. Problem	Pick from a dropdown: Missed record, Wrong taxable value, Wrong rate, Wrong place of supply, Wrong B2B/B2C type, Missed credit or debit note, Wrong recipient GSTIN, Earlier month record
D. Effect	Tax up or tax down, and the amount from the books
E. Route	`=IF(OR(C2="Wrong recipient GSTIN",C2="Earlier month record"),"Next GSTR-1 (not 1A)","GSTR-1A before 3B")`
F. Touches Table 3.2?	Yes if it is an inter-State supply to an unregistered person, composition taxpayer or UIN holder
G. Fixed in	GSTR-1A ARN and date, or the month of the later GSTR-1
H. Fixed?	`=IF(G2<>"","DONE","OPEN")`

Tab "Window": one row per client

Column	What to write
A. Client	Name and GSTIN; monthly filers only on this tab
B. GSTR-1 filed on	Date of the October 2026 GSTR-1
C. GSTR-1A opens	`=IF(B2="","GSTR-1 not filed",MAX(B2,DATE(2026,11,11)))`
D. GSTR-3B due	`=DATE(2026,11,20)` (monthly filers; check for any extension notified for the client's State)
E. Open fixes	`=COUNTIFS('Fix list'!A:A,A2,'Fix list'!E:E,"GSTR-1A before 3B",'Fix list'!H:H,"OPEN")`
F. GSTR-1A filed on	Date and ARN (leave blank if no fix is needed)
G. GSTR-3B filed on	Date
H. Status	`=IF(G2<>"",IF(E2>0,"3B FILED: fix in next GSTR-1","DONE"),IF(E2=0,"READY FOR 3B",IF(F2<>"","1A FILED: check 3B values",IF(TODAY()>D2-3,"FILE 1A NOW","FIX IN 1A"))))`. The 3-day warning is our working rule, not a legal one

Tab "3.2 check": before you file GSTR-3B

Columns: State (place of supply), supplies to unregistered persons, to composition taxpayers, to UIN holders, each from the sales register for October; then the same three from GSTR-3B Table 3.2 as auto-populated; then a difference column =B2-E2 (and so on).
Any difference other than zero goes back to the "Fix list" with problem type Wrong place of supply or Wrong B2B/B2C type, and is corrected in GSTR-1A, because Table 3.2 cannot be edited in GSTR-3B.
Remember GSTR-1A is filed once: collect every fix for the client first, then file it in one go.

Tab "Open": what still needs action

=FILTER('Fix list'!A2:H,'Fix list'!H2:H="OPEN",'Fix list'!A2:A<>"") lists every record not yet fixed. Sort by client, then check the "Window" status before anyone files GSTR-3B.

Made-up example (not a real client)

Example client M, a monthly filer, filed October GSTR-1 on 10 November. On 12 November the accountant finds one B2B invoice left out, one inter-State sale to an unregistered buyer reported with the wrong State, and one invoice issued to the wrong GSTIN. The first two go on the "Fix list" as "GSTR-1A before 3B" and are filed together in one GSTR-1A on 16 November; the 3.2 check now matches. The wrong-GSTIN invoice cannot be changed in GSTR-1A, so it is marked "Next GSTR-1 (not 1A)" and handled in the November GSTR-1. GSTR-3B is filed on 18 November.

Plan for 11 to 20 November

Wed 11 Nov: GSTR-1 for October due. As each one is filed, ask the client for any invoice or credit note issued in October that is not in it.
12 to 16 Nov: compare the sales register with the filed GSTR-1 and the auto-populated GSTR-3B; fill the "Fix list" and the "3.2 check".
By Tue 17 Nov: file one GSTR-1A per client that needs it, then reopen GSTR-3B and confirm the values changed.
By Fri 20 Nov: file GSTR-3B. Make sure no client has records saved in GSTR-1A but not filed, or GSTR-3B will not go through.

WhatsApp message to a client

"Hello, your October GST sales return has been filed. If any October invoice, credit note or debit note was missed or has a wrong amount, State or rate, please send it to us by 14 November. We can correct it once before your GSTR-3B is filed (due 20 November); after that it has to wait for next month's return."

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Sources

CBIC Notification No. 12/2024 – Central Tax, 10 July 2024 (rule 59(1) proviso, rule 59(4A), FORM GSTR-1A and its instructions)
GST portal user guide: FAQs on Form GSTR-1A (window, once only, no nil, GSTIN, saved records)
GST portal user guide: Form GSTR-3B (due dates, auto-population, editing)
GSTN advisories on the GST portal (services.gst.gov.in, Advisories): "Advisory on reporting values in Table 3.2 of GSTR-3B" (5 Dec 2025) and "Advisory regarding non-editable of auto-populated liability in GSTR-3B" (7 Jun 2025)

This sheet is a working aid, not professional advice. Due dates and portal behaviour can change; check the GST portal before you rely on them. The example client is made up. Checked on 25 October 2026. Spot an error? Write to mininglife7@gmail.com.

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Unadhi Guides are free, independent explainers. We correct errors as soon as we find them: write to mininglife7@gmail.com.