Tax Due Dates September 2026: Every Deadline, Form and Penalty in One Calendar
September is the month Indian compliance teams quietly dread, and 2026 has made it harder than usual. The tax due dates September 2026 calendar is the first September in living memory that runs on two income tax statutes at the same time: the Income-tax Act, 1961 still governs the FY 2025-26 audit you are closing, while the Income-tax Act, 2025 governs the TDS you deposit and the advance tax you pay this month.
Get that distinction wrong and you will quote the wrong section, tag the wrong year on a challan, or file the wrong form. This guide maps every one of the tax due dates September 2026 brings — the exact date, the form, the governing law, the penalty, and, just as importantly, the three widely circulated deadlines that no longer exist at all.
Tax Due Dates September 2026: The Complete Master Calendar
Before the detail, here is the whole month on one page. Every entry below has been checked against the position published on incometax.gov.in and gst.gov.in. Where a date is sector-specific rather than universal, the applicability column says so plainly.
| Date | Day | Obligation | Form | Who it applies to |
|---|---|---|---|---|
| 7 Sep | Monday | Deposit TDS and TCS deducted or collected in August 2026 | Challan | All non-government deductors and collectors |
| 10 Sep | Thursday | GST TDS return for August 2026 | GSTR-7 | Notified deductors under GST |
| 10 Sep | Thursday | GST TCS return for August 2026 | GSTR-8 | E-commerce operators |
| 11 Sep | Friday | Outward supplies for August 2026 | GSTR-1 | Monthly filers |
| 13 Sep | Sunday | Invoice Furnishing Facility for August 2026 | IFF | QRMP taxpayers (optional) |
| 13 Sep | Sunday | Return for August 2026 | GSTR-5 | Non-resident taxable persons |
| 13 Sep | Sunday | ITC distribution for August 2026 | GSTR-6 | Input Service Distributors |
| 14 Sep | Monday | TDS certificate for tax deducted in July 2026 | Form 132 | Deductors in challan-cum-statement cases |
| 15 Sep | Tuesday | Second instalment of advance tax, 45% cumulative | Challan | All taxpayers liable under Section 404 |
| 15 Sep | Tuesday | Statement where August TDS or TCS paid without a challan | Form 137 | Government offices |
| 15 Sep | Tuesday | Client code modification statement for August 2026 | Form 1 | Stock exchanges |
| 15 Sep | Tuesday | Provident fund and ESI contributions for August 2026 | ECR / ESI challan | All covered employers |
| 20 Sep | Sunday | Summary return and tax payment for August 2026 | GSTR-3B | Monthly filers |
| 20 Sep | Sunday | Return for August 2026 | GSTR-5A | OIDAR service providers |
| 25 Sep | Friday | Tax payment for August 2026, second month of the quarter | PMT-06 | QRMP taxpayers |
| 28 Sep | Monday | Inward supply statement for August 2026 | GSTR-11 | UIN holders claiming refund |
| 30 Sep | Wednesday | Challan-cum-statement for TDS deducted in August 2026 | Form 141 | Property, rent, contractor and VDA deductors |
| 30 Sep | Wednesday | Tax audit report for AY 2026-27 | 3CA or 3CB with 3CD | Taxpayers covered by Section 44AB |
| 30 Sep | Wednesday | Audit report for AY 2026-27 | Form 10B / 10BB | Trusts, funds, hospitals, institutions |
| 30 Sep | Wednesday | Annual general meeting for FY 2025-26 | AGM | Companies with 31 March year end |
Pro Tip — the Sunday trap. In 2026, both 13 September and 20 September fall on a Sunday. GST due dates do not automatically shift to the next working day, and the portal accepts filings all weekend. What does not work on a Sunday is your bank’s high-value payment window. If GSTR-3B carries a cash liability, arrange the payment by Friday 18 September.
Why September 2026 Runs on Two Income Tax Acts at Once
Most compliance calendars published this month list dates without saying which law creates them. That works in an ordinary year. It fails badly in 2026, because the Income-tax Act, 2025 came into force on 1 April 2026 while the Income-tax Act, 1961 continues to govern everything that happened before that date.
The test is simple once you see it. Ask which period the money belongs to. Income earned up to 31 March 2026 belongs to FY 2025-26 and Assessment Year 2026-27, and therefore to the old Act. Anything paid or credited from 1 April 2026 belongs to Tax Year 2026-27 and the new Act.
What the old Act still governs in September
The tax audit report you are racing to finish is an FY 2025-26 document. It is filed in Form 3CA or Form 3CB together with Form 3CD, under Section 44AB of the 1961 Act. The consolidated Form 26 introduced by the new law applies from Tax Year 2026-27 onward, which means the first Form 26 audit is a 2027 problem, not a 2026 one. Filing this year’s audit on the new form would be rejected.
The same reasoning applies to the audit reports for charitable trusts in Form 10B and Form 10BB, and to the audited return itself, due 31 October 2026.
What the new Act governs in September
Every rupee of TDS you deduct this month, every advance tax instalment you pay, and every challan-cum-statement you file sits under the Income-tax Act, 2025. The practical consequences are specific:
- Section numbers changed. Salary TDS now sits in Section 392 and non-salary TDS in Section 393. Advance tax liability sits in Section 404, with shortfall interest in Sections 424 and 425 rather than the familiar 234B and 234C.
- Form numbers changed. Forms 26QB, 26QC, 26QD and 26QE are consolidated into a single Form 141. The TDS certificate in these cases is now Form 132.
- Year tagging changed. Challans for April 2026 onward must be tagged to Tax Year 2026-27, not Assessment Year 2026-27. This is the single most common error of the transition, and it is expensive to unwind.
Expert Insight. A challan tagged to AY 2026-27 instead of Tax Year 2026-27 does not bounce. The money reaches the exchequer, the receipt generates normally, and everything looks fine until the quarterly statement is processed. Then the credit appears against FY 2025-26 records, the return shows a short-payment default that does not actually exist, and you spend weeks on a correction. Check the year field before you press pay, not after.
If your team is still mapping old forms to new ones, our detailed breakdown of the TDS forms for FY 2026-27 sets out every renumbering alongside the payment codes.
7 September: Depositing August TDS Without Losing a Month of Interest
The first of the tax due dates September 2026 arrives on Monday 7 September. Tax deducted or collected during August 2026 must reach the Central Government by this date. The timeline is prescribed by Rule 218 of the Income-tax Rules, 2026, which carries forward the position of the old Rule 30 without any change of policy.
Who pays by when
- Non-government deductors: 7 September 2026 for August deductions.
- Government deductors paying by challan: the same 7 September date applies.
- Government deductors remitting by book adjustment: the same day as deduction. There is no seven-day cushion, and this catches out government undertakings every single quarter.
The interest arithmetic most people get wrong
Interest on late deposit runs at 1.5% per month or part of a month, calculated from the date of deduction — not from 7 September. That distinction is worth real money.
Client scenario. A Gurugram digital agency deducted ₹2,40,000 of TDS across August 2026, with the earliest deduction dated 3 August. The accounts team deposited on 9 September, two days late. Because interest runs from the date of deduction, the period from 3 August to 9 September spans parts of two months. The charge is 1.5% for each, so 3% on ₹2,40,000 — ₹7,200 for a two-day slip. Had they paid on 6 September, the cost would have been nil.
There is a second, quieter penalty. A quarterly statement cannot be filed until the tax it reports has actually been deposited. A late deposit in September therefore threatens the Q2 statement due on 31 October, where the late filing fee under Section 427 of the Income-tax Act, 2025 runs at ₹200 per day, capped at the amount of tax in that statement.
Preparing your quarterly TDS statement?
Build and validate Q2 in the browser before you upload it to TRACES.
10 to 13 September: The GST Window That Decides Your Buyer’s ITC
The middle of the first fortnight belongs entirely to GST. Four separate returns fall due across four days, and the sequencing matters more than most businesses realise.
10 September — GSTR-7 and GSTR-8
Notified deductors file GSTR-7 for GST TDS, and e-commerce operators file GSTR-8 for GST TCS, both for August 2026. These are narrow-population returns, but they feed the electronic cash ledger of the supplier. A late GSTR-8 leaves a seller unable to see the credit that has already been collected from them.
11 September — GSTR-1, the return that moves other people’s money
Monthly filers report August outward supplies in GSTR-1 by 11 September. This is the most commercially consequential of all the tax due dates September 2026 carries, because GSTR-1 populates your customer’s GSTR-2B.
File it late, and your buyer’s input tax credit slides into the next month’s statement. They still pay you in full, and they still fund the GST — they simply cannot claim it yet. In a working-capital-tight market, that conversation damages relationships far more than a late fee does.
Client scenario. A Jaipur textile trading firm filed August GSTR-1 four days late in a previous cycle. Their largest customer, a garment exporter, found ₹4.1 lakh of ITC missing from the GSTR-2B they had already budgeted against. The exporter had to fund the tax from working capital for a full month. The supplier’s own late fee was under ₹250. The renegotiated payment terms that followed cost considerably more.
13 September — IFF, GSTR-5 and GSTR-6
Three filings share this date, and 13 September 2026 is a Sunday:
- IFF — optional for QRMP taxpayers who want their August B2B invoices to reach buyers early rather than waiting for the quarterly GSTR-1.
- GSTR-5 — non-resident taxable persons.
- GSTR-6 — Input Service Distributors distributing credit to branches.
Pro Tip — GSTR-1A is now the correction route. Auto-populated inter-state supply figures in Table 3.2 of GSTR-3B are locked and pull directly from GSTR-1. If August outward supplies were reported incorrectly, you must correct them through GSTR-1A before filing GSTR-3B on 20 September. Editing inside GSTR-3B is no longer available. That makes an accurate 11 September filing considerably more valuable than it used to be.
For the mechanics of preparing and validating the return itself, the step-by-step material in our complete GST guide walks through each table, and the free GSTR-1 preparation tool checks your invoice data before upload.
14 and 15 September: Certificates, Advance Tax and Payroll
14 September — Form 132
Deductors who filed a challan-cum-statement for July 2026 must issue the corresponding TDS certificate in Form 132 by 14 September. This is the new Act’s replacement for the old Forms 16B, 16C and 16D. If you bought property, paid rent above the threshold as an individual, or made a covered payment in July, this is the certificate your deductee needs.
15 September — the second advance tax instalment
For most taxpayers, 15 September is the single most important of the tax due dates September 2026 presents. The second instalment of advance tax for Tax Year 2026-27 falls due, and the requirement is 45% of estimated full-year tax liability, cumulatively.
Advance tax applies under Section 404 of the Income-tax Act, 2025 where estimated liability for the year, after TDS and TCS credits, is ₹10,000 or more. Resident senior citizens aged 60 and above without business or professional income remain exempt.
The cumulative calculation, worked through
The word cumulative does the heavy lifting here, and misreading it is the most common advance tax error in India.
| Instalment | Due date | Cumulative % required | Payable this instalment |
|---|---|---|---|
| First | 15 June 2026 | 15% | 15% |
| Second | 15 September 2026 | 45% | 30% |
| Third | 15 December 2026 | 75% | 30% |
| Fourth | 15 March 2027 | 100% | 25% |
Client scenario. Anitha, a Bengaluru independent software consultant, estimates her Tax Year 2026-27 liability at ₹4,80,000. Her clients have already deducted ₹1,20,000 of TDS, leaving a net advance tax requirement of ₹3,60,000. She paid ₹54,000 in June, being 15%.
By 15 September she must have paid 45% of ₹3,60,000, which is ₹1,62,000. Subtracting the June payment, her September cheque is ₹1,08,000 — not ₹1,62,000, and not 45% all over again. Both mistakes are made routinely, one costing interest and the other costing cash flow.
Pro Tip — re-estimate, do not repeat. The commonest failure is copying June’s number into September. Half the year is now visible. Fold in the actual April to August position, any capital gains booked, rent received, interest credited on fixed deposits, and any client who has stopped deducting TDS. Interest under Section 425 of the Income-tax Act, 2025 applies at 1% per month on the shortfall in each instalment, and it is computed automatically.
Not sure what your 45% actually works out to?
Enter your estimated income and TDS credits to get the exact September instalment.
For a fuller treatment of the instalment mechanics, thresholds and interest computation, see our dedicated guide to advance tax for FY 2026-27.
15 September — payroll statutory dues
Employers must deposit provident fund contributions through the ECR and ESI contributions for August 2026 by the same date. PF delays attract interest at 12% per annum plus damages, and unpaid employee contributions can be treated far more seriously than an ordinary tax default. Professional tax deadlines vary by state; Maharashtra employers also work to 15 September for August.
20 to 28 September: GSTR-3B, PMT-06 and the Sunday Problem
The back half of the month is where the tax due dates September 2026 brings turn into cash outflows rather than paperwork.
20 September — GSTR-3B and the tax itself
Monthly filers submit GSTR-3B for August 2026 and, critically, discharge the tax on the same date. Businesses often treat GSTR-3B as a filing deadline. It is a payment deadline first. Interest at 18% per annum runs on any unpaid liability from the day after the due date, and it is calculated on the net cash liability.
OIDAR service providers file GSTR-5A on the same date. And 20 September 2026 is a Sunday, so the earlier warning applies with full force.
25 September — PMT-06 for QRMP taxpayers
Taxpayers in the Quarterly Return Monthly Payment scheme do not file a monthly GSTR-3B. They pay instead. PMT-06 for August 2026, being the second month of the July to September quarter, is due on 25 September. The quarterly GSTR-3B follows in October, on 22 or 24 October depending on whether your state falls in Category X or Category Y.
28 September — GSTR-11
Holders of a Unique Identity Number, typically embassies, UN bodies and notified agencies claiming a refund of GST paid on inward supplies, file GSTR-11 for August 2026 by 28 September.
Expert Insight — reconcile before you file, not after. The single highest-value hour in the GST month is spent matching GSTR-2B against your purchase register before GSTR-3B goes in. Credit claimed that is not in GSTR-2B becomes a departmental query. Credit sitting in GSTR-2B that you failed to claim is money left on the table. Our free GST ITC reconciliation tool does this comparison in the browser.
The 30 September Cliff: Tax Audit, Form 141, Form 10B and the AGM
Four unrelated obligations converge on Wednesday 30 September 2026. For any business of reasonable size, all four apply.
The tax audit report under Section 44AB
The audit report for FY 2025-26 must be furnished by 30 September 2026 where the corresponding income tax return is due on 31 October 2026. Transfer pricing cases work to 31 October for the report and 30 November for the return.
Thresholds for AY 2026-27 are unchanged:
- Business: turnover above ₹1 crore, rising to ₹10 crore where cash receipts and cash payments each stay within 5% of the total.
- Profession: gross receipts above ₹50 lakh.
- Presumptive opt-outs: those declaring income below the presumptive rate while exceeding the basic exemption limit, regardless of turnover.
Why 30 September is really an October deadline
The audit is not a single filing. It is a chain: books closed, audit completed, report uploaded by the chartered accountant, report accepted by the taxpayer on the portal, and only then the return filed by 31 October. Each link takes calendar time, and the last link depends on a valid digital signature that nobody checks until the day it fails.
Client scenario. A Coimbatore engineering firm with ₹14 crore turnover handed its books to the auditor on 18 September. The Form 3CD reconciliation between turnover in the financial statements and turnover reported in GSTR-1 threw up a ₹38 lakh gap, caused by credit notes recorded in the books but never reported on the GST portal. Resolving it took eleven days. The report went up on 29 September with a single day to spare, and only because the promoter’s DSC happened to be current. Firms that start in the first week of September do not have this experience.
Form 141 for August deductions
The challan-cum-statement for tax deducted under Section 393 during August 2026 is due on 30 September. Form 141 now covers what used to be four separate forms — property purchases, rent paid by individuals and HUFs above the threshold, certain contractor and professional payments, and virtual digital asset transfers.
Form 10B and Form 10BB
Charitable trusts, funds, hospitals, universities and other institutions furnish their audit report for AY 2026-27 by 30 September. Choosing incorrectly between Form 10B and Form 10BB renders the filing defective, and the threshold conditions determining which applies should be checked before the auditor begins, not after.
The annual general meeting
Companies with a 31 March 2026 financial year end must hold their AGM by 30 September 2026. The AGM date then starts two clocks: AOC-4 within 30 days and MGT-7 or MGT-7A within 60 days. Our ROC compliance checklist sets out the full sequence.
Three Tax Due Dates September 2026 Does Not Actually Have
This is the section that separates a current calendar from a recycled one. Three deadlines widely listed for September 2026 are simply wrong, and two of them will cost you either wasted professional fees or a missed deadline elsewhere.
1. DIR-3 KYC is no longer due on 30 September
Director KYC was an annual 30 September filing for years. It is not any more. The Ministry of Corporate Affairs notified the Companies (Appointment and Qualification of Directors) Amendment Rules, 2025 vide G.S.R. 943(E) dated 31 December 2025, in force from 31 March 2026. The substituted Rule 12A moves director KYC to a once-in-three-years intimation, filed on or before 30 June of the year following every third consecutive financial year.
Two further changes came with it. The separate DIR-3 KYC e-form and DIR-3 KYC Web have been merged into a single Form DIR-3 KYC Web. And a change in mobile number, email or residential address triggers an event-based update within 30 days, independent of the three-year cycle.
Pro Tip. A director who completed KYC for FY 2025-26 has nothing to file in September 2026, and nothing in FY 2027-28 either, absent a change in particulars. If a compliance vendor has invoiced you for a 30 September 2026 DIR-3 KYC filing, check the rule before you pay. The current position is available on mca.gov.in.
2. The income tax return is not due on 15 September 2026
The 15 September ITR date circulating widely belonged to AY 2025-26, when the deadline was extended. It has been copied forward into 2026 calendars without checking. The actual position for AY 2026-27:
| Taxpayer category | Return | Due date |
|---|---|---|
| Salaried, pensioners, capital gains, other sources | ITR-1, ITR-2 | 31 July 2026 |
| Business or profession, no audit required | ITR-3, ITR-4 | 31 August 2026 |
| Audit cases | ITR-3, ITR-5, ITR-6 | 31 October 2026 |
| Transfer pricing cases | With Form 3CEB | 30 November 2026 |
| Belated return | Any | 31 December 2026 |
If you missed 31 July or 31 August, September is a belated filing month, not a due-date month. A late fee under Section 234F of ₹5,000 applies, reduced to ₹1,000 where total income does not exceed ₹5 lakh, alongside interest under Section 234A on unpaid tax.
3. GSTR-9 and GSTR-9C are not September filings
The GST annual return and reconciliation statement for FY 2025-26 are due on 31 December 2026. September is the right month to begin the reconciliation work, and entirely the wrong month to expect a deadline.
The Silent Deadline: GST Returns That Close Forever This Month
There is one September deadline that appears on no official calendar because it is different for every taxpayer, and it is permanent.
The Finance Act, 2023 inserted a three-year outer limit for filing returns under Sections 37, 39, 44 and 52 of the CGST Act, operationalised through Notification No. 28/2023 – Central Tax dated 31 July 2023. The GST portal began enforcing it from 1 October 2025. Once three years pass from a return’s due date, the portal will not accept it. Ever.
Applied to September 2026, that means the August 2023 tax period closes this month:
| Return | Tax period | Original due date | Bars permanently on |
|---|---|---|---|
| GSTR-1 | August 2023 | 11 September 2023 | 11 September 2026 |
| GSTR-6 | August 2023 | 13 September 2023 | 13 September 2026 |
| GSTR-3B | August 2023 | 20 September 2023 | 20 September 2026 |
Expert Insight — what the bar does not do. Being unable to file does not extinguish the liability. The tax, interest and late fee remain recoverable, and departmental assessment powers continue to operate over the barred period. Worse, where a supplier’s GSTR-1 was never filed, those outward supplies never reached the buyer’s GSTR-2B, and the buyer’s own claim is separately governed by the time limit in Section 16(4). A supplier can be brought back into compliance while the customer’s credit stays permanently lost.
The action is straightforward: pull your return filing status from the portal this week and file anything approaching its three-year mark before the date passes. Advisories on this are published at cbic.gov.in and step-by-step filing help at tutorial.gst.gov.in.
What Missing Each September 2026 Deadline Actually Costs
Deadlines feel abstract until the numbers are on the table. Every one of the tax due dates September 2026 sets carries a specific, quantified cost when missed. Here is what each default costs, with the governing provision.
| Default | Charge | Provision |
|---|---|---|
| Late deposit of TDS | 1.5% per month from the date of deduction | Income-tax Act, 2025 |
| Failure to deduct TDS | 1% per month from the date it was deductible | Income-tax Act, 2025 |
| Late quarterly TDS statement | ₹200 per day, capped at the tax in that statement | Section 427 |
| Advance tax instalment shortfall | 1% per month on the shortfall | Section 425 |
| Advance tax below 90% of assessed tax | 1% per month from 1 April 2027 | Section 424 |
| Late GSTR-1 or GSTR-3B with tax payable | ₹50 per day, being ₹25 CGST and ₹25 SGST | CGST Act |
| Late nil GSTR-1 or GSTR-3B | ₹20 per day, being ₹10 CGST and ₹10 SGST | CGST Act |
| Unpaid GST | 18% per annum on net cash liability | Section 50, CGST Act |
| Tax audit report not furnished | 0.5% of turnover, capped at ₹1,50,000 | Section 271B |
| Belated income tax return | ₹5,000, or ₹1,000 where income is up to ₹5 lakh | Section 234F |
| AGM not held by 30 September | Up to ₹1,00,000 plus ₹5,000 for each further day | Companies Act, 2013 |
| Late PF or ESI deposit | 12% per annum interest plus damages | EPF and ESI Acts |
Read that table alongside the calendar and a pattern emerges. The cheapest defaults are the GST late fees. The expensive ones are interest-based, because interest compounds across months and does not respect part-month arithmetic. A one-day TDS delay and a thirty-day TDS delay can cost exactly the same.
Key Takeaways
- Five dates carry most of the risk: 7 September for TDS deposit, 11 September for GSTR-1, 15 September for advance tax, 20 September for GSTR-3B, and 30 September for the tax audit report and AGM.
- Two Acts run side by side. The audit is a 1961 Act filing; the TDS, advance tax and Form 141 are 2025 Act obligations. Tag every challan to Tax Year 2026-27, never AY 2026-27.
- Advance tax on 15 September is cumulative. The requirement is 45% of the year’s liability in total, which usually means paying a further 30%.
- 13 and 20 September are Sundays. GST due dates do not shift, so treat the preceding Friday as your working deadline.
- DIR-3 KYC is not due this month. It moved to a once-in-three-years filing due 30 June, effective 31 March 2026.
- The ITR is not due on 15 September 2026. That was AY 2025-26. September is a belated filing month for AY 2026-27.
- The August 2023 GST period bars permanently this month — 11 September for GSTR-1 and 20 September for GSTR-3B, with no condonation available.
- Interest is the expensive part, not the late fee. TDS interest runs from the date of deduction and a part-month counts as a full month.
Frequently Asked Questions
What are the most important tax due dates September 2026 for a small business?
Five dates carry the most risk. Deposit August TDS by 7 September, file GSTR-1 for August by 11 September, pay the second advance tax instalment by 15 September, file GSTR-3B and pay the GST by 20 September, and complete the tax audit report along with the annual general meeting by 30 September 2026. Everything else in the month is either sector specific or applies to a narrower category of taxpayer.
Is the income tax return due on 15 September 2026?
No. The 15 September income tax return deadline belonged to AY 2025-26, when the date was extended. For AY 2026-27 the due dates are 31 July 2026 for ITR-1 and ITR-2, 31 August 2026 for ITR-3 and ITR-4 in non-audit cases, 31 October 2026 for audit cases and 30 November 2026 for transfer pricing cases. What falls on 15 September 2026 is the second instalment of advance tax, not the return.
Is DIR-3 KYC still due on 30 September 2026?
No. The Ministry of Corporate Affairs replaced annual director KYC with a once-in-three-years filing through the Companies (Appointment and Qualification of Directors) Amendment Rules, 2025, notified vide G.S.R. 943(E) dated 31 December 2025 and effective from 31 March 2026. The filing is now made in Form DIR-3 KYC Web on or before 30 June of the year following every third consecutive financial year. Only an event-based update, within 30 days of a change in mobile number, email or address, is required in between.
How much advance tax must be paid by 15 September 2026?
At least 45 percent of your estimated total tax liability for Tax Year 2026-27, measured cumulatively. Because 15 percent was already due by 15 June 2026, the September payment is usually the remaining 30 percent. Advance tax applies under Section 404 of the Income-tax Act, 2025 when the estimated liability after TDS and TCS credits reaches Rs 10,000 or more.
Do GST due dates shift when they fall on a Sunday?
No automatic shift applies. In September 2026 both 13 September and 20 September fall on a Sunday, and the GST portal accepts filings on weekends and public holidays. Unless the CBIC issues a specific notification extending the date, the deadline stands. Treat the working day before as your real cut-off, because bank cut-off timings for tax payment can lag portal availability.
What happens if the tax audit report is not filed by 30 September 2026?
Section 271B of the Income-tax Act, 1961 allows a penalty of 0.5 percent of total sales, turnover or gross receipts, capped at Rs 1,50,000. The bigger practical consequence is sequencing: the audited return for AY 2026-27, due 31 October 2026, cannot be filed until the auditor has uploaded the report and the taxpayer has accepted it on the portal. A delayed audit therefore pushes the return into belated territory as well.
Which GST returns become permanently time-barred in September 2026?
Returns under Sections 37, 39, 44 and 52 of the CGST Act cannot be filed after three years from their due date. In September 2026 that closes the August 2023 period: GSTR-1 for August 2023 was due 11 September 2023 and bars on 11 September 2026, while GSTR-3B for August 2023 was due 20 September 2023 and bars on 20 September 2026. Once barred there is no condonation route, and the underlying tax, interest and late fee still remain recoverable.
Which income tax Act applies to the September 2026 deadlines?
Both. The Income-tax Act, 2025 governs money paid or credited from 1 April 2026, so it covers the 7 September TDS deposit, the 15 September advance tax instalment and the 30 September Form 141 statement. The Income-tax Act, 1961 continues to govern income earned in FY 2025-26, so the 30 September tax audit report is still filed in Form 3CA or 3CB with Form 3CD, not the new Form 26.
Conclusion
The tax due dates September 2026 calendar is not difficult because there are many dates. It is difficult because the dates belong to two different statutes, two different tax periods and four different regulators, and because at least three widely circulated September deadlines are no longer real.
Work it in the order the month gives you. Clear the TDS deposit on 7 September while your August register is fresh. Treat 11 September as a commitment to your customers rather than a filing chore. Re-estimate rather than repeat on 15 September. File and pay by Friday 18 September so the Sunday deadline never matters. And start the audit conversation now, because 30 September is only a real deadline for firms that began in August.
One habit removes most of the risk: put every one of these tax due dates September 2026 into a shared calendar with alerts at seven days and one day, and review the position against the official portals rather than a recycled blog table. Rules changed twice this year already.
Disclaimer: This content is for information and education only and does not constitute professional, tax, legal, or investment advice. Consult a qualified professional before acting. Due dates, forms and rates are subject to change by notification; verify the current position on incometax.gov.in, gst.gov.in and cbic.gov.in before filing.
