GST return filing in 2026 is not the forgiving, fix-it-later system it used to be. Over the last year the portal quietly turned strict: your GSTR-3B is now hard-locked to your GSTR-1 data, the Invoice Management System decides what input credit you can claim, and returns older than three years are permanently blocked. For a regular business, getting returns right the first time has gone from good practice to the only option. This guide explains the main returns, their deadlines, and the new controls that now make accuracy non-negotiable.
Quick answer: Most regular taxpayers file GSTR-1 (outward sales — by the 11th monthly) and GSTR-3B (summary and tax payment — by the 20th monthly; staggered to the 22nd/24th under the quarterly QRMP scheme). Since July 2025, GSTR-3B's outward-liability figures are auto-locked from GSTR-1 (corrections only via GSTR-1A before filing 3B). The Invoice Management System (IMS) is effectively mandatory from April 2026 and now gates your input tax credit. From January 2026, any return more than three years past its due date is permanently blocked.
The main GST returns
For a regular registered business, the workhorses are:
- GSTR-1 — details of outward supplies (your sales), invoice by invoice. This data flows to your buyers.
- GSTR-3B — a summary return where you declare total sales, claim input tax credit (ITC), and pay the tax.
- GSTR-2B — an auto-generated statement of your eligible ITC, produced on the 14th of each month (not filed by you).
- GSTR-9 / 9C — the annual return and reconciliation statement for applicable taxpayers.
- CMP-08 / GSTR-4 — for composition scheme taxpayers.
Small taxpayers (turnover up to ₹5 crore) can opt for the QRMP scheme — quarterly returns with monthly tax payment, using the Invoice Furnishing Facility (IFF) to upload invoices monthly.
Filing deadlines
| Return | Who / frequency | Typical due date |
|---|---|---|
| GSTR-1 | Monthly filers | 11th of the next month |
| GSTR-1 (IFF) | QRMP, optional monthly upload | 13th of the next month |
| GSTR-3B | Monthly filers | 20th of the next month |
| GSTR-3B | QRMP (quarterly) | 22nd or 24th, by state group |
| GSTR-9 | Annual (if applicable) | 31 December of next FY |
Dates can be extended by notification (for instance, the March 2026 GSTR-3B was extended to 21 April 2026), so always confirm on the GST portal.
GSTR-3B hard-locking: the big change
Since the July 2025 tax period, the outward-liability tables in GSTR-3B (Tables 3.1 and 3.2) are auto-populated from your GSTR-1/IFF and locked — you can no longer manually edit those figures on the portal. There's no "proceed anyway." If your GSTR-1 is wrong, your GSTR-3B is wrong, and the only fix is to correct the GSTR-1 data first. This single change is why GSTR-1 accuracy now matters more than ever.
⚠️ ITC (Table 4) hard-locking is expected to follow (Phase 2, around mid-2026), which will restrict your credit to exactly what flows from GSTR-2B. Reconcile now.
GSTR-1A: the correction route
To fix an error in a filed GSTR-1 for the same tax period, use GSTR-1A — an amendment form you can file after GSTR-1 but before GSTR-3B for that period. It's useful for correcting a wrong GSTIN, taxable value, or tax amount, or responding to a buyer's rejection. Note: GSTR-1A can be filed only once per period and cannot be revised, so compile all corrections before opening it.
The Invoice Management System (IMS)
IMS is the new gatekeeper for input tax credit. Every invoice your supplier uploads lands in your IMS dashboard, where you Accept, Reject, or keep Pending each one. Only accepted invoices flow into your GSTR-2B and become claimable ITC. The rule that catches everyone: inaction equals acceptance — if you do nothing before GSTR-2B generates, the invoice is deemed accepted and enters your credit, errors and all. IMS became fully operational on 1 October 2025 and is effectively mandatory from April 2026, with the portal blocking ITC on invoices not reflected in GSTR-2B. Build a weekly IMS review (ideally before the 14th) into your routine.
The 3-year filing lock
From 1 January 2026, GST returns — including GSTR-1, GSTR-3B, GSTR-4 and GSTR-5 — cannot be filed once three years have passed from their original due date. After that line, the period is permanently blocked, and any unreported tax or unclaimed ITC for it is effectively lost (while your exposure to demand and penalty continues). If you have old pending returns, file them before they cross the three-year mark.
Late fees and interest
- Late fee: broadly ₹50 per day (₹25 CGST + ₹25 SGST) for returns with tax, and ₹20 per day for nil returns, subject to caps.
- Interest: 18% per annum on any tax paid late, under Section 50.
- Late GSTR-1 also delays your buyers' ITC, which strains business relationships.
Also note GST 2.0: from 22 September 2025, the rate structure was rationalised toward mainly 5% and 18% slabs (the 12% and 28% slabs were largely removed). Make sure your invoices carry the correct current rate, or you risk non-compliant invoices.
Worked example
A trader files GSTR-1 by the 11th. A supplier mistakenly uploads an invoice to the trader's GSTIN for ₹1,80,000 instead of ₹18,000. Because inaction = acceptance in IMS, if the trader doesn't reject it before GSTR-2B generates on the 14th, the inflated ITC flows into the locked GSTR-3B — a credit the trader isn't entitled to, inviting reversal and 18% interest later. The fix is simple but time-sensitive: review IMS weekly, reject the wrong invoice, and only accepted, correct invoices feed the return.
Common mistakes
- Ignoring IMS. Unreviewed invoices are deemed accepted into your ITC.
- Errors in GSTR-1. They now flow straight into a locked GSTR-3B.
- Trying to "adjust" GSTR-3B manually. Outward-liability fields are locked; fix GSTR-1 via GSTR-1A.
- Sitting on old returns. The 3-year lock makes them unfilable.
- Billing at outdated rates. Check GST 2.0 rates on every invoice.
Checklist
- File GSTR-1 accurately by the 11th (or IFF by the 13th under QRMP).
- Review your IMS dashboard weekly and action every invoice before the 14th.
- Use GSTR-1A to fix same-period errors before filing GSTR-3B.
- File and pay GSTR-3B by the 20th (or 22nd/24th under QRMP).
- Clear any pending returns before they cross the 3-year lock.
- Confirm invoices carry correct GST 2.0 rates.
Frequently asked questions
What are the due dates for GSTR-1 and GSTR-3B? GSTR-1 is due by the 11th and GSTR-3B by the 20th of the following month for monthly filers; QRMP filers have staggered quarterly dates.
Can I edit GSTR-3B if my GSTR-1 had an error? No. Outward-liability fields are hard-locked from GSTR-1. Correct the data through GSTR-1A before filing GSTR-3B.
What is IMS in GST? The Invoice Management System, where you accept, reject, or pend supplier invoices. Only accepted invoices give you ITC, and no action means deemed acceptance.
What happens to GST returns older than three years? From January 2026, they're permanently blocked and can no longer be filed.
What is the interest on late GST payment? 18% per annum on the tax paid late, plus applicable late fees.
This article is for legal awareness and education only and is not tax or legal advice. GST rules and dates change frequently by notification; confirm current requirements on the GST portal or consult a qualified professional.