The last two years brought the most significant changes to GST since its introduction. Some were headline news — the rate rationalisation approved by the GST Council in September 2025 — while others were quiet portal changes with a bigger effect on day-to-day compliance. Here is what a business in Mumbai or Thane should have built into its monthly process by now, and where we still see gaps.
1. The simplified rate structure
From 22 September 2025 the four main slabs of 5%, 12%, 18% and 28% were rationalised into two principal rates — 5% and 18% — with a 40% rate for a short list of demerit and luxury goods. Most items that were at 12% moved to 5% and most at 28% moved to 18%. For businesses the practical work was updating HSN-wise rate masters in billing software, re-pricing contracts, dealing with transitional issues on stock and advances, and passing on the benefit. If your rate master has not been reviewed against the current notifications, a rate audit is overdue: charging the old rate exposes you to demands with interest, while under-charging is a cost you cannot recover from customers.
2. The Invoice Management System (IMS)
Introduced in October 2024, IMS lets a recipient accept, reject or keep pending each invoice, debit note and credit note uploaded by suppliers before GSTR-2B is generated on the 14th. What began as optional has become central: rejected documents drop out of your 2B, pending documents are carried forward, and credit notes now have direct consequences for the supplier's liability. Businesses that ignore IMS are effectively accepting every document by default — including duplicates and invoices belonging to someone else. We recommend actioning IMS between the 12th and 14th of every month and keeping the rejection reasons on file.
3. Hard-locked GSTR-3B liability
From the July 2025 tax period, the outward tax liability auto-populated in GSTR-3B from GSTR-1 / IFF can no longer be edited in the return. Corrections must be made through GSTR-1A before filing 3B. This closes the door on the old habit of adjusting 3B figures at the last minute and puts the burden on getting GSTR-1 right. In practice it means the sales register must be final by the 11th, and any credit notes or amendments must be reported in the same cycle.
4. The three-year time limit on returns
The portal now bars filing of GSTR-1, GSTR-3B, GSTR-4, GSTR-5, GSTR-6, GSTR-7, GSTR-8 and GSTR-9 more than three years after their due date. Any business with old unfiled returns — commonly from a period when the business was dormant or a registration was pending cancellation — should regularise immediately, because once the window closes the return cannot be filed at all, with consequences for input credit, cancellation applications and departmental proceedings.
5. E-invoice reporting within 30 days
Businesses with aggregate annual turnover of ₹10 crore or more must report e-invoices to the Invoice Registration Portal within 30 days of the invoice date; the portal rejects older invoices. Combined with the IMS mechanism, a delayed IRN means your customer cannot see or accept the invoice in time — and may withhold payment. Integrate IRN generation with invoicing rather than batching it at month-end.
6. Registration and refund process changes
New registrations are subject to risk-based processing with biometric Aadhaar authentication at facilitation centres in Maharashtra and most other states, and a streamlined approval track for low-risk applicants. Refunds for exports and inverted duty continue to be processed on a risk-scored basis with provisional sanction, so the quality of the RFD-01 statements determines the timeline.
7. The GST Appellate Tribunal
With the GST Appellate Tribunal now constituted and accepting appeals, businesses with orders from the first appellate authority that were previously stuck have a forum. Limitation periods for filing before the Tribunal were set by notification — if you have a pending first-appeal order, check the date by which the second appeal must be filed.
What this means for your monthly process
Sales data final by the 11th; IMS actioned by the 14th; GSTR-2B reconciled to the purchase register before the 20th; vendors with missing invoices chased in the same month; and an annual HSN and rate review. If any of these steps is missing from your calendar, talk to us about a GST health check.
Tax, GST and business setup advisors — Mumbai and Thane. Contact us to discuss your situation.
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