The ordinary due date of the GST annual return (GSTR-9) for financial year 2025-26 is 31 December 2026. GSTR-9C, where applicable, follows the same clock unless a separate notification is issued. Turnover thresholds for who must file 9 and 9C have been moved before; the notification in force for that year is the authority. A 9 that is written without a 3B–1–books bridge will only record the mismatch. See GST and refunds, which should not be claimed against a year whose annual return is still fiction.
Update
GSTR-9 / 9C for FY 2025-26 — ordinary due date 31 December 2026
The annual GST return and, where applicable, the reconciliation statement, follow the books and the monthly returns — not the other way round.