GSTR-3B Lock: What's Locked, What Isn't, and the Three-Year Time Bar

“Is GSTR-3B locked?” Partly. Since the July 2025 tax period, the tax liability that the GST portal fills in from your GSTR-1 can't be changed in GSTR-3B. Since November 2025, Table 3.2 is locked too, and the portal now refuses returns that are more than three years past their due date. But the input tax credit in Table 4 is not locked: as of 7 October 2026, GSTN has not issued the advisory it promised before doing that. This guide sets out what is locked, what isn't, and how to fix a mistake, with a link to the official GSTN advisory for every date.

What is locked in GSTR-3B today

On 7 October 2026 we read every advisory on the GST portal's News and Updates page from December 2023 to 1 October 2026. Dates and rules come from those advisories. Check the portal before you rely on them, because GSTN can defer or change a rollout. Re-checked on 15 October 2026: the newest GSTN advisory is still the 13 October 2026 note on GSTR-9/9C, and there is no ITC-lock advisory.

The liability lock and Table 3.2

The portal gives you a pre-filled GSTR-3B. Your tax liability comes from the sales you reported in GSTR-1, GSTR-1A or IFF, and your input tax credit comes from GSTR-2B. Until mid-2025 you could overwrite the liability figures in GSTR-3B itself. That is no longer allowed:

• Auto-populated tax liability: non-editable from the July 2025 tax period. GSTN first planned this for January 2025, deferred it, and brought it in from July 2025.
• Table 3.2 (inter-state supplies to unregistered persons, composition taxpayers and UIN holders): non-editable from the November 2025 tax period. GSTR-3B must be filed with the system values in this table.
• What it means in practice: if GSTR-3B shows the wrong liability, the mistake is in your GSTR-1 data. Fix it there (through GSTR-1A) before you file GSTR-3B, or report the correction in a later GSTR-1 or IFF.

Is ITC locked in GSTR-3B? Not yet

Many posts say the input tax credit in GSTR-3B will be locked “from July 2026”. We could not find any GSTN advisory announcing this. The official position is still GSTN's 17 October 2024 advisory: locking of auto-populated ITC “will be implemented from a later date” and “a separate advisory would be issued” after the trade's IMS issues are addressed. No such advisory appears in the GST portal's news up to 1 October 2026.

Two related changes are official, though:

• ITC still flows from GSTR-2B. GSTN's 8 October 2025 advisory confirms ITC continues to auto-populate from GSTR-2B into GSTR-3B, that GSTR-2B is still generated on the 14th, and that you can act on records in the Invoice Management System (IMS) until you file GSTR-3B and regenerate GSTR-2B.
• Hard checks on two parts of Table 4 were announced. GSTN's 29 December 2025 advisory said that “shortly” GSTR-3B can't be filed if the ITC you reclaim (Table 4D(1)) or the reverse-charge credit you claim (Tables 4A(2) and 4A(3)) is more than the matching ledger allows. That is a validation, not a lock on the GSTR-2B figures. The advisory gives no go-live date, so check the portal when you file.

If you read a claim that ITC is now locked, look for the GSTN advisory behind it. If there isn't one, treat it as unconfirmed.

How to fix a mistake: GSTR-1A

GSTR-1A was introduced by Notification 12/2024-Central Tax and has been available since the July 2024 tax period. According to GSTN's GSTR-1A advisory and its Table 3.2 FAQs:

• It is optional and can be filed only once for a tax period.
• It opens after you file GSTR-1, or after GSTR-1's due date if that is later, and stays open until you file GSTR-3B for the same period. There is no other cut-off date.
• You can add a missed sale or correct one reported in that period's GSTR-1 or IFF. The change shows up in GSTR-3B (including Table 3.2) straight away.
• Your buyer gets the credit for supplies added or amended through GSTR-1A in their GSTR-2B for the next tax period.
• QRMP taxpayers get a quarterly GSTR-1A covering the quarter's GSTR-1 and any IFF filed in months 1 and 2.
• If you have already filed GSTR-3B, GSTR-1A for that period is closed. Report the correction in the amendment tables of a later GSTR-1 or IFF.

1. Before the GSTR-1 due date, check the draft GSTR-1 against your sales register: buyer GSTINs, place of supply, rates, B2B vs B2C, credit notes.
2. File GSTR-1, then open the system-generated GSTR-3B PDF and compare the liability with your books.
3. If anything is wrong, file GSTR-1A for the same period. Remember you get one chance.
4. Check that GSTR-3B (including Table 3.2) now shows the right figures, take IMS actions on purchases, confirm the tax liability breakup and file.

The three-year time bar

The Finance Act, 2023 bars a return from being filed more than three years after its due date. The rule has been in force since 1 October 2023 (Notification 28/2023-Central Tax) and covers returns under Sections 37, 39, 44 and 52. GSTN's 29 October 2025 advisory lists GSTR-1, GSTR-1A, GSTR-3B, GSTR-4, GSTR-5, GSTR-5A, GSTR-6, GSTR-7, GSTR-8 and GSTR-9/9C.

Enforcing it on the portal took longer. GSTN first said early 2025, then the July 2025 tax period, and finally the November 2025 tax period. Its example periods barred from 1 December 2025:

The time bar keeps moving: each month, another month's returns pass the three-year mark. If you have unfiled returns from late 2023, file them first, then the rest in date order. GSTR-3B can't be filed while earlier returns are pending. Late fees and interest still apply; see the GST late fee calculator.

Other GSTR-3B changes in 2026

• Interest in Table 5.1 (from the January 2026 period): the portal now works out interest on late tax payment, allowing for the lowest cash-ledger balance between the due date and the payment date (proviso to Rule 88B(1)). The amount is filled in your next GSTR-3B. You can't lower it, but you can raise it if your own calculation is higher.
• Tax liability breakup (pre-filled from the January 2026 period; confirmation needed from February 2026): the portal pre-fills which earlier periods your tax relates to, based on document dates in GSTR-1/1A/IFF. From the February 2026 period, open the tab on the payment page and click SAVE (or edit it) before filing. GSTN's March 2026 advisory said the step was then required even when all tax was for the current period, and that a fix was in progress.
• Interest re-computation: where February 2026 interest was calculated wrongly, use the “RE-COMPUTE INTEREST” button under Table 5.1. An edited figure can't go below the recomputed one.

Timeline of GSTN advisories

A monthly routine that works with the lock

1. Bill every sale as a proper GST invoice with the buyer's GSTIN, HSN, rate and place of supply. With the liability lock in place, mistakes in your GSTR-1 data end up in GSTR-3B.
2. By the 10th, review the month's sales and credit notes. For the GSTR-1 steps, see how to file GSTR-1.
3. File GSTR-1 (or IFF), then check the auto-filled GSTR-3B and its PDF.
4. Use GSTR-1A once, if needed, to correct the period before filing GSTR-3B.
5. From the 14th, act on purchase records in IMS and check GSTR-2B against your purchase register before claiming ITC.
6. Confirm the tax liability breakup, check interest in Table 5.1, pay and file GSTR-3B by the due date.
7. Keep a list of any unfiled returns and clear the oldest first, before they pass three years.

Can you file GSTR-3B before the 14th?

Yes. GSTN's advisories set no “not before the 14th” rule: once the month (or quarter) is over, you can file GSTR-3B on any day up to the due date. The catch is input tax credit. GSTN generates GSTR-2B on the 14th of the following month (advisory of 8 October 2025), and ITC auto-fills into GSTR-3B from it. File before the 14th and that period's GSTR-2B doesn't exist yet, so you lose the auto-filled ITC figures and the IMS step of accepting, rejecting or keeping supplier invoices pending. Credit you claim must still match invoices your suppliers have reported, because under Section 16(2)(aa) of the CGST Act ITC is allowed only on invoices that appear in your GSTR-2B. That's why most businesses file GSTR-1 by the 11th and GSTR-3B between the 14th and the due date. Two more points: QRMP filers get GSTR-2B only for the last month of the quarter, and GSTR-2B isn't generated at all while the previous period's GSTR-3B is pending (advisory of 16 November 2024).

For how the two returns relate in general, read GSTR-1 vs GSTR-3B.

How VelBooks helps

The lock leaves one practical rule: get GSTR-1 right the first time. In VelBooks, every bill carries the buyer's GSTIN, HSN code, rate, place of supply and CGST/SGST or IGST split, and purchases are recorded in the same place. GSTR filing and return management works from those same records, so you can check your sales data before it is locked into GSTR-3B. VelBooks runs in the browser and comes with a free 30-day trial at app.velbooks.com.

Sources

• GSTN: hard-locking of auto-populated liability in GSTR-3B (17 Oct 2024)
• GSTN: liability lock not implemented from January 2025 (27 Jan 2025)
• GSTN: auto-populated liability non-editable from July 2025 (7 Jun 2025)
• GSTN: reporting values in Table 3.2 of GSTR-3B, with FAQs (5 Dec 2025)
• GSTN: advisory for Form GSTR-1A (26 Jul 2024)
• GSTN: barring of GST returns after three years (29 Oct 2024)
• GSTN: barring of GST returns after three years (7 Jun 2025)
• GSTN: file pending returns before expiry of three years (29 Oct 2025)
• GSTN: important advisory on IMS (8 Oct 2025)
• GSTN: important advisory on GSTR-2B and IMS (16 Nov 2024)
• GSTN: credit reversal/reclaim and RCM ITC statements (29 Dec 2025)
• GSTN: interest collection and related enhancements in GSTR-3B (30 Jan 2026, PDF)
• GSTN: tax liability breakup confirmation in GSTR-3B (16 Mar 2026)
• GSTN: re-computation of interest in Table 5.1 (16 Apr 2026, PDF)

This article is general information, not legal or tax advice. Rules change; check the official sources above or consult your tax adviser.