GSTR-3B and IMS in 2026: What Is Locked, What Is Not, and What Each IMS Action Does

Two changes to GSTR-3B are real and in force: the tax liability that comes from GSTR-1 is locked, and IMS decides what reaches GSTR-2B. A third, a lock on the input tax credit in Table 4, has been widely reported and does not appear in anything GSTN has issued.

What is locked

• Auto-populated liability, from the July 2025 tax period. GSTN's advisory of 7 June 2025 says the liability auto-populated from GSTR-1, GSTR-1A and IFF becomes non-editable from the July 2025 period, the return filed in August 2025. The way to change it is an amendment through GSTR-1A for the same tax period, filed before GSTR-3B.
• Table 3.2, from the November 2025 tax period. The advisory of 5 December 2025 makes the auto-populated values of inter-state supplies to unregistered persons, composition taxpayers and UIN holders non-editable. GSTR-1A can be filed at any time until GSTR-3B is filed, and amendments can also go in a later GSTR-1 or IFF.
• Returns older than three years. Under the Finance Act, 2023, a return cannot be filed after three years from its due date. GSTN's advisory of 29 October 2025 applied the bar on the portal from the November 2025 tax period; among the first barred from 1 December 2025 were GSTR-3B for October 2022 and GSTR-9 and 9C for FY 2020-21.
• A confirmation step, from the February 2026 tax period. The advisory of 16 March 2026 requires the "Tax Liability Breakup, As Applicable" tab on the payment page to be confirmed and saved before GSTR-3B can be filed.

What is not locked: the ITC in Table 4

GSTN's GSTR-3B FAQ, as published on 12 September 2026, still says the auto-populated values are kept editable. If Table 4A is edited upwards, the tile turns red and a warning is shown, but the return can be filed.

On 8 October 2025 GSTN issued an advisory headed "Attention: Important Advisory on IMS" to answer posts circulating about changes from 1 October 2025. Its first point: "No Change in Auto-Population of ITC", with ITC continuing to auto-populate from GSTR-2B to GSTR-3B.

We read GSTN's news and updates from January to September 2026. None of them locks Table 4. Should that change, it will arrive as a GSTN advisory, not as a forwarded post.

What each IMS action does

The IMS rules that decide a month

• The window closes with GSTR-3B. Actions can be taken from the time the supplier saves a record until the recipient files GSTR-3B for that period, and not after.
• After the 14th, recompute. A draft GSTR-2B is generated on the 14th. Any action taken after that, or any change to an earlier action, requires GSTR-2B to be recomputed from the IMS dashboard.
• GSTR-2B is sequential. GSTR-2B for a period is generated only if GSTR-3B for the previous period has been filed.
• Pending has two clocks. An ordinary invoice kept pending can be availed later, but not beyond the limit in section 16(4). Credit notes and the other specified records can be kept pending for one tax period only, from the October 2025 period.
• Some records never reach IMS. Reverse-charge supplies reported by the supplier in Table 4B, and records whose ITC is not available under section 16(4) or the place-of-supply rule, go straight to GSTR-3B.
• Imports are now in IMS. From the October 2025 period, Bills of Entry for imports of goods, including from SEZs, appear in IMS and are deemed accepted if no action is taken.
• Bulk actions have a tool. GSTN's IMS Offline Tool, an Excel-based utility introduced on 21 April 2026, takes actions on individual and bulk invoices.

Many GSTINs, many clocks

Each registration files its own GSTR-3B, so each has its own IMS window, its own draft GSTR-2B on the 14th and its own sequence. An unfiled GSTR-3B for one GSTIN holds back only that GSTIN's next GSTR-2B, and a credit note kept pending under one registration runs on that registration's tax period.