GSTR-3B is locked, and returns now expire. Two GST changes that are not reversible

GST compliance has absorbed a steady stream of procedural change since 2017, most of it adjustable after the event. Two recent changes are different in kind: they remove the ability to correct things later. Neither is dramatic on the day it lands. Both are expensive the first time somebody discovers them at the wrong moment.

The outward liability in GSTR-3B is hard-locked

Since the July 2025 tax period, the outward tax liability auto-populated into GSTR-3B from GSTR-1 has been non-editable. Until then, a difference between the two — a wrong invoice value, a missed credit note, a supply reported in the wrong place — could simply be corrected in GSTR-3B before filing, and the two returns would disagree quietly.

That route is closed. A correction now has to be made in GSTR-1A, which sits between GSTR-1 and GSTR-3B for exactly this purpose, and it has to be made before GSTR-3B is filed. Once GSTR-3B goes in, the period is settled on the figures that came across.

A return more than three years old cannot be filed

The second change is blunter. Once three years have run from the original due date of a return, that return can no longer be filed. Not with a late fee, not with interest, not after an order. The period closes.

The bar became fully operative in January 2026 and applies across the returns — GSTR-1, 3B, 4, 5, 6, 7, 8 and 9 alike. What is caught inside a closed period stays there: unreported outward tax, and equally, input tax credit that was never claimed.

• A registration that stopped filing during a dispute, intending to regularise once the dispute ended, may find the early periods have closed while the dispute ran.
• A dormant registration that was never surrendered accumulates unfiled returns quietly, and they begin expiring on schedule.
• A business that took over a registration on acquisition inherits the unfiled history and the clock that is already running on it.

There is no appellate remedy for this, because it is not a penalty. The facility to file simply ceases to exist.

The annual deadline that costs the most money

Neither of the above is the deadline that most often causes an avoidable loss. That remains the outer limit for amending an invoice, claiming input tax credit, or issuing a credit note for the previous financial year: 30 November of the following year, or the date the annual return is filed, whichever comes earlier.

Credit not claimed by then is not recoverable, and the reason it was missed makes no difference — the supplier filed late, the invoice was in a drawer, the accounts were with someone else. It is worth putting a review in the calendar for October each year rather than November, so that anything found still has somewhere to go.

A reasonable response

• Move the outward-supply reconciliation to before GSTR-1 is filed, and treat GSTR-1A as the correction route rather than the exception.
• Take an inventory of every GST registration the business holds, including ones nobody has looked at in years, and check what is unfiled and how old it is.
• Put an annual credit review in October, ahead of the November limit.
• Where a period has already closed, the question is no longer how to file it but how to present the position if it is examined. That is a different exercise, and it is better started early.