GSTR-3B Table 3 Is Locked: What to Automate Before Your GSTR-1 Goes Out

Since the July 2025 tax period, Table 3 of GSTR-3B takes its outward liability from GSTR-1 and GSTR-1A and cannot be edited. So the checking has to happen before GSTR-1 goes out. At Bitvyas we automate those pre-filing checks (sales register against e-invoices, e-way bills and the draft GSTR-1) plus IMS suggestions; an accountant approves every filing.

Table 4, input tax credit, is still not locked. That is the short version. The rest of this article covers what the lock changed about the monthly GST cycle, which checks AI can run for you, and which decisions stay with a person.

What is locked in GSTR-3B, as of 30 September 2026?

Only Table 3, the auto-populated outward liability. We re-checked on 30 September 2026 and found no GSTN advisory that locks Table 4 ITC.

For the full record of how the Table 3 lock arrived, and why the "April 2026 ITC hard block" some sites describe has no advisory behind it, see the FAQ at the end.

Why does the lock move the work to before GSTR-1?

Because GSTR-3B no longer gives you a second chance on outward liability. Whatever GSTR-1 (and GSTR-1A, if filed) says is what Table 3 shows.

Before July 2025, a team could file GSTR-1 on the 11th, spot a missed invoice or a wrong rate a week later and adjust the figure in GSTR-3B. That option is gone. You still have GSTR-1A, but only until GSTR-3B for the same period is filed, and filing an amendment return is extra work for something a check could have caught earlier.

The e-invoice side tightens this further. Your e-invoices flow into GSTR-1 automatically, so an error at the invoice registration portal becomes an error in GSTR-1 and then in Table 3. And if your aggregate turnover is ₹10 crore or more, an invoice that was never reported to the IRP cannot be reported once it is more than 30 days old.

Put together, the useful checks now sit in the first ten days of the month, and some of them are daily rather than monthly.

What does the pre-filing check look like when it is done by hand?

In many finance teams and CA practices it still looks like this. Someone exports the sales register from Tally, Zoho Books or the ERP. Someone downloads the e-invoice and e-way bill data. The three are lined up in a spreadsheet with lookups, differences are chased, and the GSTR-1 draft is reviewed table by table before the 11th.

It works. It is also the kind of work that gets squeezed when the month-end close overlaps with the filing dates, and the checks that matter most (missing IRNs, cancelled invoices with live e-way bills) are the ones most likely to be skipped under time pressure.

Where does AI take over?

On matching, explaining and drafting; not on filing. We set these up as three checks and one inward-side workflow.

Check 1: sales register against e-invoices (run daily)

• Every B2B invoice, credit note and debit note in the books is matched to an IRN, on GSTIN, document number, date, taxable value, tax and HSN.
• Invoices with no IRN are flagged with the number of days left in the 30-day window, where that window applies.
• Differences are labelled in plain words: "rate differs", "credit note missing IRN", "invoice cancelled in books, IRN still active".

Check 2: e-invoices against e-way bills

• Each e-way bill is matched to its invoice on document number, value and GSTIN.
• The check flags e-way bills whose invoice was cancelled or amended, invoices that needed an e-way bill but have none, and values that differ.
• These are the mismatches a tax officer can see in the government's own data, so they are worth catching first.

Check 3: draft GSTR-1 against the books (before the 11th)

• The auto-populated tables (4A, 4B, 6A, 9B, 12) are compared with the sales register, along with the B2C tables that are uploaded rather than auto-populated.
• It flags documents edited after auto-population (the IRN link is cleared when that happens), HSN summary differences, and B2B invoices that landed in B2C.
• The output is one exception list. Each line says what is wrong, why it is probably wrong, and the suggested fix: correct the books, correct the GSTR-1 draft, or file GSTR-1A before GSTR-3B.

The inward side: IMS suggestions and supplier follow-ups

• For each invoice in IMS, the system suggests accept, reject or pending, based on the purchase register, the goods receipt and past behaviour of that supplier, and writes the reason next to it.
• It drafts supplier emails or WhatsApp messages for invoices missing from IMS or carrying the wrong value, and tracks replies.
• It lists credit notes kept pending, so none is carried past the one period IMS allows.
• The matching itself is the same engine we described in GSTR-2B reconciliation automation.

The inputs are the exports and downloads your team already takes: the ERP or Tally sales and purchase registers, and the JSON or Excel files from the GST, e-invoice and e-way bill portals. Where a business already has a GSP connection, the same checks can read from it.

What stays with a person?

Every decision that carries a legal consequence. In our setups the accountant or CA:

1. Approves the GSTR-1 filing. AI prepares the exception list and the suggested corrections; a person decides and files.
2. Decides IMS rejections. Rejecting an invoice affects the supplier's position as well as yours. The system suggests; it does not click.
3. Decides on credit-note ITC reductions, where the amount to reverse needs judgement.
4. Chooses between fixing now and filing GSTR-1A. That depends on the client and the materiality.
5. Handles any notice (DRC-01C, DRC-01B or a scrutiny letter). The pack is assembled automatically; the reply is a professional's.

This split is the same one we use for every process: AI takes the repeated matching and chasing, and a person keeps the sign-off. We explain how we pick which process to automate first in what to automate with AI first.

What does the monthly cycle look like with this in place?

For a monthly filer, the rhythm we set up looks like this:

Quarterly (QRMP) filers follow the same sequence on their own dates.

FAQ

Is ITC locked in GSTR-3B?

No. As of 30 September 2026, Table 4 input tax credit is not hard-locked. The only locked part is Table 3, since the July 2025 tax period. GSTN's advisory of 17 October 2024 said locking of auto-populated ITC would come "from a later date" through a separate advisory, and we have not found that advisory. Articles describing an April 2026 or July 2026 ITC hard block cite no advisory number; the more careful ones describe it as "expected" or "targeted". If you claim more ITC than GSTR-2B shows, the portal does not stop you: Rule 88D applies afterwards, through Form DRC-01C, with seven days to pay or explain.

How did the Table 3 lock come about?

GSTN announced it on 17 October 2024 for the January 2025 period, deferred it on 27 January 2025, and implemented it by an advisory of 7 June 2025 from the July 2025 tax period, with corrections moving to GSTR-1A. The lock came by advisory, not by an amendment to the Act.

Can I still correct outward liability?

Yes, through GSTR-1A, filed after GSTR-1 and before GSTR-3B for the same period. The corrected value flows into GSTR-3B. Once GSTR-3B is filed, GSTR-1A for that period is closed.

Do we need new software for these checks?

Not necessarily. The checks read the registers you already keep in Tally, Zoho Books or your ERP, and the files you already download from the government portals. What changes is who does the matching: the system, every day, instead of a person, at month-end.

Sources

• GSTN advisory on non-editable auto-populated liability in GSTR-3B, 7 June 2025, as reproduced by TaxGuru
• GSTN, FAQs on GSTR-1A
• GSTN, Advisory on auto-population of e-invoice details into GSTR-1
• GSTN advisory on the 30-day e-invoice reporting limit for AATO of ₹10 crore and above, 5 November 2024, as reproduced by GSTGyaan
• GSTN advisories on IMS and GSTR-2B, 9 and 17 October 2025, summarised by TaxGuru
• Rule 88D, CGST Rules, 2017 (Form GST DRC-01C), inserted by Notification No. 38/2023-Central Tax
• Lakshmikumaran & Sridharan, "Hard-locking GSTR-3B: A new compliance milestone and its pitfalls", 30 June 2025, via Lexology

Related

• What to automate with AI first: 8 business processes mapped
• GSTR-2B reconciliation: how to automate ITC matching
• AI reconciliation for finance teams and AI for accounting and tax firms

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Regulatory position checked on 30 September 2026. If GSTN issues an advisory locking ITC in Table 4, we will update this page with its date and scope. This is general information, not tax advice for your specific facts.

Update history: first published 26 September 2026 as an explainer on what is hard-locked; re-angled on 30 September 2026 to cover the automated checks that the Table 3 lock calls for.