Last updated: 1 September 2026. September repeats August's shape — six filing dates, all monthly, no quarterly return anywhere — with one twist: the 13th and the 20th are both Sundays, and a GST due date does not move because the calendar is inconvenient. One deadline also quietly expires for the quarter — 13 September is the last Invoice Furnishing Facility upload before the July–September quarter closes in October. Here is every date, who it binds, and what slipping costs.
Applicability Note: This guide reflects GST provisions and CBIC notifications applicable as of 1 September 2026. Due dates change through CBIC notifications — extensions are issued from time to time and the GST portal is the authoritative source. No September 2026 extension has been notified as of this writing. Always verify on gst.gov.in or with a GST professional before filing.
Who Should Care?
This guide applies to:
- Regular GST taxpayers filing GSTR-1 and GSTR-3B monthly — turnover above ₹5 crore in the previous financial year, or anyone who has opted out of QRMP
- QRMP scheme taxpayers — August is Month 2 of the July–September quarter, so the IFF (13 September) and PMT-06 (25 September) are both live, and the IFF does not come back this quarter
- TDS deductors under Section 51 and e-commerce operators collecting TCS under Section 52
- Non-resident taxable persons, Input Service Distributors, OIDAR providers and UIN holders
- Anyone who has been told a GST deadline rolls forward when it lands on a Sunday — see section 2
1. September 2026 GST Deadline Calendar at a Glance
| Due Date | Return / Form | Period Covered | Who Files |
|---|---|---|---|
| 10 September 2026 (Thu) | GSTR-7, GSTR-8 | August 2026 | TDS deductors, e-commerce TCS operators |
| 11 September 2026 (Fri) | GSTR-1 | August 2026 | Monthly filers (turnover > ₹5 crore or opted out of QRMP) |
| 13 September 2026 (Sun) | IFF (optional), GSTR-5, GSTR-6 | August 2026 | QRMP filers, non-resident taxpayers, ISDs |
| 20 September 2026 (Sun) | GSTR-3B, GSTR-5A | August 2026 | Monthly filers, OIDAR service providers |
| 25 September 2026 (Fri) | PMT-06 | August 2026 | QRMP filers (Month 2 challan) |
| 28 September 2026 (Mon) | GSTR-11 | August 2026 | UIN holders (embassies, UN agencies, notified persons) |
Subject to notification changes — verify on the GST portal before filing.
2. The Two Sundays — 13 and 20 September
This is the only unusual thing about September 2026, and the internet is confident and divided on it.
No CBIC notification shifts a GST due date because it falls on a Sunday or a public holiday. The dates in Rule 59, Rule 61, Rule 63 and the rest are fixed by day of the month, with no weekend carve-out. Late fee under Section 47 runs from the day after the due date, and the portal computes it automatically — nobody reviews the calendar first.
The widely repeated claim that a deadline rolls to the next working day comes from Section 10 of the General Clauses Act, 1897, and the reason it does not help here is in the text of the section. It applies where an act is directed to be done "in any Court or office on a certain day", and then only "if the Court or office is closed on that day or the last day of the prescribed period". Its premise is a shut office. A GST return is furnished on the common portal, which does not observe Sundays, and we could locate no CBIC notification or circular applying Section 10 to GST return due dates. Treat the 13th and the 20th as hard dates.
Where the weekend actually bites: the money, not the return
The filing is electronic; the cash is not always. Under Rule 87(3), a deposit into the electronic cash ledger can be made by internet banking, UPI, IMPS, credit or debit card, NEFT or RTGS — all electronic — or over the counter at an authorised bank, but only up to ₹10,000 per challan per tax period, by cash, cheque or demand draft. UPI and IMPS were added by Notification No. 14/2022 - Central Tax dated 5 July 2022; older payment guides still list only the pre-2022 modes.
A Sunday due date means the counter is shut. And under the first proviso to Rule 87(2), a FORM GST PMT-06 challan "shall be valid for a period of fifteen days" — generate one on the 1st, forget it, and it has lapsed before the 20th. Clear the cash ledger by Friday 11 September for the 13th and Friday 18 September for the 20th, and the Sunday question stops mattering.
3. Monthly Filers — 11 and 20 September
11 September 2026: GSTR-1 for August 2026
GSTR-1 reports all outward supplies for August 2026 — B2B and B2C invoices, debit and credit notes, exports and amendments. The data flows into your buyer's GSTR-2B and decides the ITC they can claim, which is why filing GSTR-1 before GSTR-3B remains the standard sequencing.
Late fee: ₹50 per day total (₹20 for nil returns), subject to turnover-based caps. GSTR-1 does not attract interest directly, but tax shortfalls caused by missing invoices do. Table 12 runs under the Phase-3 HSN rules — codes selected from a dropdown, B2B and B2C split into separate tables; our guide to HSN reporting in GSTR-1 covers the 4-digit versus 6-digit split. Between filing GSTR-1 and GSTR-3B for the same period you can use GSTR-1A to amend or add invoices, so the corrected liability lands in the same month's GSTR-3B.
20 September 2026: GSTR-3B for August 2026, and GSTR-5A
GSTR-3B is the monthly summary return declaring outward supplies, inward supplies, eligible Input Tax Credit — subject to the four conditions under Section 16 — and net tax payable for August 2026. This is where tax is actually paid. The 20th is uniform across all states for monthly filers; the 22nd/24th split applies only to the QRMP quarterly return, which does not fall in September.
Late fee: ₹50 per day total (₹20 for nil returns), subject to turnover-based caps. Interest under Section 50 runs at 18% per annum, and under the proviso to Section 50(1) it applies only to the net cash component of a late GSTR-3B — the portion paid through the cash ledger, not the part set off by ITC.
GSTR-5A falls on the same date and is filed by OIDAR providers based outside India supplying digital services to unregistered persons in India. Its late fee is not GSTR-5's: it attracts the full Section 47 fee of ₹200 per day total (₹100 per Act), because the reduction once available to it under Notification No. 6/2018 - Central Tax dated 23 January 2018 was rescinded by Notification No. 13/2018 - Central Tax dated 7 March 2018. Plenty of published calendars still carry the withdrawn figure.
4. QRMP Filers — the Last IFF of the Quarter, and the Month 2 Challan
August is Month 2 of the July–September quarter, so both QRMP items run this month — and one of them is running for the last time this quarter.
13 September 2026: IFF for August 2026 (optional, and final for the quarter)
The Invoice Furnishing Facility lets QRMP filers push B2B invoices to their buyers mid-quarter instead of making them wait for the quarterly GSTR-1. It is optional, available for Months 1 and 2 of a quarter only, capped at ₹50 lakh of invoice value per month, and due by the 13th.
What makes this date matter more than August's is what follows it: there is no IFF for September, because September is Month 3 and settles directly in the quarterly return. Any August B2B invoice not uploaded by 13 September — and every September invoice — reaches your buyer's GSTR-2B only when the quarterly GSTR-1 is filed on 13 October 2026. Skipping the IFF costs no late fee. It costs your customer a month of waiting for credit, on the last occasion this quarter when you could have prevented it.
25 September 2026: PMT-06 for August 2026
PMT-06 is the monthly tax deposit for QRMP filers, due the 25th for Months 1 and 2 of a quarter. Two methods: the fixed sum method — 35% of the tax paid in cash in the previous quarter, pre-filled by the portal as a challan — or the self-assessment method, computing August's actual liability net of available ITC.
No return is filed with PMT-06; it is a challan. Interest at 18% per annum applies on shortfalls, though the fixed sum method carries a safe harbour: pay the pre-filled amount by the due date and no interest arises on that instalment even if the actual liability turns out higher, provided the quarter's full liability is discharged by the quarterly GSTR-3B due date (Circular No. 143/13/2020-GST dated 10 November 2020). September's tax settles in that quarterly return, not by a third challan.
5. Other Returns Falling in September 2026
10 September 2026: GSTR-7 (TDS) and GSTR-8 (TCS)
Both fall on the same Thursday and are routinely confused, but their late fees sit under different notifications and are not the same figure.
GSTR-7 captures TDS deducted under Section 51, filed by government departments and other notified deductors for August 2026. Late fee: ₹50 per day total (₹25 under each of CGST and SGST), capped at ₹2,000 total (₹1,000 per Act), with a complete waiver for nil-TDS months. The reduction was notified by Notification No. 22/2021 - Central Tax dated 1 June 2021 and superseded by Notification No. 23/2024 - Central Tax dated 8 October 2024 (effective 1 November 2024), which retained both figures and added the nil-month waiver.
GSTR-8 is filed by e-commerce operators collecting TCS under Section 52 for the same period. TCS runs at 0.5% of net taxable supplies — 0.25% CGST plus 0.25% SGST, or 0.5% IGST — per Notification No. 15/2024 - Central Tax dated 10 July 2024. Late fee: ₹200 per day total (₹100 per Act), capped at ₹10,000 total (₹5,000 per Act); no reduction notification analogous to GSTR-7's exists. Interest at 18% per annum applies to delayed TDS and TCS payment alike.
13 September 2026: GSTR-5 and GSTR-6
GSTR-5 is filed by non-resident taxable persons doing business in India temporarily, covering August 2026 supplies. The due date is the 13th — it moved with effect from 1 October 2022, and the older date still circulates in outdated calendars. Its reduced fee rests on Notification No. 5/2018 - Central Tax dated 23 January 2018. GSTR-6 is filed by Input Service Distributors to report ITC received and distributed to recipient units; late fee ₹50 per day total (₹25 per Act) per Notification No. 7/2018 - Central Tax dated 23 January 2018, capped at ₹10,000 total (₹5,000 per Act), with no separate nil-return concession notified.
28 September 2026: GSTR-11
GSTR-11 is the inward supplies statement filed by UIN holders — embassies, consulates, UN agencies and notified international organisations — claiming refunds of GST paid on inward supplies in August 2026.
6. What Is Not Due in September 2026 — and One Thing to Decide Anyway
- No quarterly return of any kind. The July–September quarter closes in October: quarterly GSTR-1 on 13 October, CMP-08 on 18 October, quarterly GSTR-3B on 22 or 24 October depending on state category.
- Nothing for composition dealers. CMP-08 for April–June was due 18 July; the next one is 18 October.
- No AATO work. The FY 2025-26 AATO (aggregate annual turnover) amendment window closed 31 July 2026 and the officer-review fortnight closed 15 August 2026. The figure that emerged is the one driving your ₹5 crore e-invoicing and QRMP thresholds.
- GSTR-9 and GSTR-9C for FY 2025-26 are due 31 December 2026, not this month. GSTR-9 is mandatory above ₹2 crore aggregate turnover, GSTR-9C additionally above ₹5 crore.
- The decision to make in September: the QRMP switch window for the October–December quarter is open from 1 August to 31 October 2026 under Rule 61A. It is not a September deadline, but it is a September decision — the quarter it governs starts before most people think about it. Our guide to opting in or out for Oct–Dec 2026 covers what changes on each side.
One dated item that is not a deadline. Press reports of an office memorandum of the GST Council Secretariat dated 29 August 2026 place the 57th GST Council meeting on Saturday 12 September 2026 in New Delhi, with an officers' meeting the previous day. That is reported, not notified — the Council's own site had published nothing on it when we checked on 1 September 2026. Nothing said at a Council meeting changes a due date by itself: a recommendation has to be given effect by notification, and none affecting September's dates is in force.
Two festival dates also fall in the month: Ganesh Chaturthi on Monday 14 September and Anant Chaturdashi on Friday 25 September, which is also the PMT-06 date. State bank holidays follow RBI's state-wise list, not a national one, and neither day shifts a GST due date — but if your state observes the 25th, move the challan up.
7. Late Fee and Interest Summary
All late fees below are total amounts under CGST + SGST combined, unless explicitly noted otherwise. Per-Act figures appear in parentheses where the breakdown is useful.
| Return | Late Fee (Regular) | Late Fee (Nil Return) | Maximum Cap | Interest on Tax |
|---|---|---|---|---|
| GSTR-1 | ₹50/day | ₹20/day | Turnover-based†: ₹2K / ₹5K / ₹10K; nil: ₹500 | N/A directly |
| GSTR-3B | ₹50/day | ₹20/day | Turnover-based†: ₹2K / ₹5K / ₹10K; nil: ₹500 | 18% p.a. on net cash tax |
| IFF | No late fee — optional facility | — | N/A | |
| PMT-06 | No late fee — challan, not a return | — | 18% p.a. on shortfall | |
| GSTR-7 (TDS) | ₹50/day (₹25 per Act) | Fully waived for nil-TDS months | ₹2,000 (₹1,000 per Act) — Notif. 22/2021-CT dated 1 Jun 2021, superseded by Notif. 23/2024-CT dated 8 Oct 2024 (eff. 1 Nov 2024) | 18% p.a. on delayed TDS |
| GSTR-8 (TCS) | ₹200/day (₹100 per Act) | — | ₹10,000 (₹5,000 per Act) | 18% p.a. on delayed TCS |
| GSTR-5 | ₹50/day (₹25 per Act) | ₹20/day (₹10 per Act) | ₹10,000 (₹5,000 per Act) | 18% p.a. (where tax due) |
| GSTR-5A | ₹200/day (₹100 per Act)‡ | No reduced nil figure asserted‡ | ₹10,000 (₹5,000 per Act) | 18% p.a. (where tax due) |
| GSTR-6 | ₹50/day (₹25 per Act) | No separate nil concession notified | ₹10,000 (₹5,000 per Act) | N/A |
† GSTR-1 / GSTR-3B late fee caps per Notification No. 19/2021, 20/2021 and 21/2021 - Central Tax, all dated 1 June 2021: turnover up to ₹1.5 crore → ₹2,000; ₹1.5–₹5 crore → ₹5,000; above ₹5 crore → ₹10,000; nil returns → ₹500. Cap figures current as of 1 September 2026 — verify on gst.gov.in.
‡ GSTR-5A does not share GSTR-5's reduced late fee. The reduction for GSTR-5A in Notification No. 6/2018 - Central Tax dated 23 January 2018 was rescinded by Notification No. 13/2018 - Central Tax dated 7 March 2018, so the full Section 47 late fee of ₹100 per day per Act (₹200 per day total) applies to returns filed on or after 7 March 2018. Sources disagree on whether any reduced nil-return figure survives, so none is stated here — verify on gst.gov.in before computing.
Key Takeaways
- Six filing dates in September 2026, all monthly. No quarterly return falls this month — the Jul–Sep quarter closes in October.
- 13 and 20 September are both Sundays and neither date moves. Section 10 of the General Clauses Act applies only where the office is closed; the portal is not. File on the date.
- The weekend risk is the payment, not the return: over-the-counter deposits are capped at ₹10,000 per challan per tax period under Rule 87(3) and need an open bank counter, and a PMT-06 challan lapses after fifteen days. Clear the cash ledger by Friday 11 September for the 13th and Friday 18 September for the 20th.
- 13 September is the last IFF of the quarter. August is Month 2; there is no IFF for September. Invoices left out wait until the quarterly GSTR-1 on 13 October to reach a buyer's GSTR-2B.
- GSTR-7 and GSTR-8 share 10 September but not their late fees: ₹2,000 total cap with a nil-month waiver versus ₹10,000 total cap. GSTR-5 is due the 13th, not the 20th.
- Not due but worth deciding: the QRMP switch window for Oct–Dec 2026 closes 31 October 2026.
Frequently Asked Questions
What is the GSTR-3B due date for August 2026?
For monthly filers, GSTR-3B for the August 2026 tax period is due 20 September 2026, uniformly across all states. That is a Sunday, and the date does not shift. QRMP filers file no GSTR-3B in September — their quarterly return for July–September is due 22 or 24 October 2026 by state category, and August's tax goes in by PMT-06 challan on 25 September.
Does a GST due date move if it falls on a Sunday?
No CBIC notification shifts it, and we could locate no CBIC circular applying Section 10 of the General Clauses Act, 1897 to GST return due dates. That section operates only where the Court or office is closed, and the common portal accepts filings on Sundays. Late fee under Section 47 runs from the day after the due date. File by the stated date.
Is the IFF compulsory for QRMP filers in September 2026?
No. The Invoice Furnishing Facility is optional, available for Months 1 and 2 of a quarter, capped at ₹50 lakh per month, and due by 13 September 2026 for August invoices. No late fee attaches to skipping it. But August is Month 2, so this is the quarter's last IFF — anything left out reaches your buyer's GSTR-2B only on the quarterly GSTR-1 of 13 October 2026.
Can I pay GST over the counter if the due date is a Sunday?
Not on the day itself — the counter is shut. Rule 87(3) allows over-the-counter deposits through authorised banks only up to ₹10,000 per challan per tax period, by cash, cheque or demand draft. The electronic modes in the same sub-rule — internet banking, UPI, IMPS, credit or debit card, NEFT and RTGS — need no counter. A PMT-06 challan is valid for fifteen days under the first proviso to Rule 87(2), so generating one far ahead does not help either.
Is CMP-08 due in September 2026?
No. CMP-08 for the April–June quarter was due 18 July 2026; the next one, for July–September, is due 18 October 2026. Composition dealers have no GST filing obligation in September 2026.
Disclaimer: This article is for informational purposes only and does not constitute professional tax advice. GST rules are subject to frequent changes through notifications and circulars. Please consult a qualified tax professional or verify the current provisions on the official GST portal (gst.gov.in) before making any compliance decisions.
Have a specific question about the September filings or your QRMP obligations? Ask our GST experts → gstconsultancy.com