Every deadline your business needs to hit in October 2026 — with the one date that closes the door on FY 2025-26 ITC permanently.

October 2026 is a month with consequences. The 20 October deadline for GSTR-3B is the final date to claim any unclaimed input tax credit from FY 2025-26. Miss it and that credit is gone permanently — no extension, no reversal, no recovery. The 31 October deadline brings the ITR for audit cases, Q2 TDS return, and ITR for domestic companies all due on the same day.

For QRMP taxpayers, October is also the quarter-end return month — the Q2 GSTR-3B (covering July, August, September) is due 22 or 24 October. And for monthly filers, the routine September GST cycle continues: GSTR-1 by 11 October, GSTR-3B by 20 October.

This blog covers every October 2026 compliance deadline, what each involves, what it costs to miss, and the specific actions to take before the month ends.

All October 2026 Compliance Deadlines at a Glance

The ITC Lapse Deadline: What Happens on 20 October 2026

This is the deadline that no other compliance calendar article typically explains with the clarity it deserves. So we will.

The rule: Under Section 16(4) of the CGST Act, input tax credit for FY 2025-26 can only be claimed until the earlier of the due date for the September 2026 GSTR-3B return, or the date of filing the annual GSTR-9 return for FY 2025-26.

The practical deadline: For monthly filers, the due date for September 2026 GSTR-3B is 20 October 2026. For QRMP filers, it is 22 or 24 October 2026.

What this means: Any purchase invoice from FY 2025-26 (April 2025 to March 2026) that has not been claimed as ITC in any GSTR-3B up to and including the September 2026 return is permanently gone after 20 October. The credit cannot be reclaimed, carried forward, or refunded.

TDS Compliance in October 2026

TDS Deposit — 7 October 2026

TDS deducted from all payments made in September 2026 must be deposited by 7 October. This includes salary TDS, contractor TDS, professional fee TDS, rent TDS, and any other payment where TDS applies under the Income Tax Act, 2025 (Section 393).

Section reference reminder: All TDS on payments made after 1 April 2026 is governed by Section 393 of the Income Tax Act, 2025. Challans and TDS returns must quote the new section references — not the old 194C, 194J, 194H etc. If your accounting software has not been updated, portal validation may fail.

Q2 TDS Return — 31 October 2026

The quarterly TDS return for July–September 2026 (Q2 of Tax Year 2026-27) must be filed by 31 October 2026. This is separate from the monthly TDS deposit obligation — the return is an independent filing that reports all deductions made during the quarter.

Key forms:

• Form 138: Salary TDS — employer deducting from employee salaries across all designations and salary structures
• Form 140: Non-salary TDS to residents — contractors, professionals, rent, interest, commission
• Form 143: TDS on payments to non-residents and foreign companies

What the Q2 return must reflect: All TDS deducted in July, August, and September 2026. All challans deposited for those months (typically by 7 August, 7 September, and 7 October). Any corrections to Q1 (April–June) TDS returns should be filed as revised returns separately — not mixed into Q2.

ITR Filing Deadlines in October 2026

ITR for Audit Cases — 31 October 2026

Businesses and professionals whose accounts are required to be audited under Section 44AB of the Income Tax Act, 1961 (applicable to FY 2025-26) must file their ITR by 31 October 2026. The tax audit report (Form 3CA/3CB/3CD) must have been uploaded by 30 September 2026.

Who this covers: 

• Business taxpayers with turnover above ₹1 crore (₹10 crore if cash transactions are below 5% of total)
• Professional taxpayers with gross receipts above ₹50 lakh (₹75 lakh under presumptive scheme if opted out)
• Any taxpayer who has triggered audit under other provisions (Section 44AD opted out in a previous year but income is below 8%/6%)

For directors and partners: If the company or firm requires an audit, the director or partner's personal ITR — if linked to the company's financials — may also have an October 31 deadline rather than the August 31 deadline. Verify with your CA which deadline applies to your personal return.

ITR for Domestic Companies — 31 October 2026

All domestic companies (private limited, public limited, OPC) must file ITR-6 for FY 2025-26 by 31 October 2026. This includes companies whose turnover is below the audit threshold — the company ITR deadline is October 31 regardless of whether a tax audit applies.

October Cash Flow Planning: Sequencing Your Compliance Obligations

October’s obligations are spread across the month but require planning from the first week. Here is the sequenced action plan:

What Each Missed Deadline Costs in October

October Has Deadlines That Cannot Be Extended. Let’s Make Sure You Hit Every One.

Related Reading

→ September 2026 GST, TDS & Advance Tax Calendar: Filing Made Simple

→ July 2026 GST & TDS Due Dates: Don’t Miss These Compliance Deadlines

→ Quarterly Review: How to Reconcile GST & Books Before Q2 Ends

→ Year-End Audit Preparation Checklist for Businesses (FY 2026-27)

The post What You Need to Know: October 2026 GST & TDS Filing Deadlines first appeared on CPC Services Pvt. Ltd..

Every deadline your business needs to hit in September 2026 — explained simply, with what each filing involves and exactly what it costs to miss it.

September is the most compliance-intensive month of the financial year for Indian businesses. Three major obligations converge in a single 30-day window: GST return filings for August, the second installment of advance tax for FY 2026-27, and the monthly TDS deposit cycle. Most crucial is furnishing of Audit Report under section 44AB (of Income-tax Act, 1961 as applicable for FY 2025-2026) on or before due date i.e. 30th September 2026. A single day delay may cost a heavy penalty which may extend to 1.50 Lakh.

For businesses with turnover above ₹5 crore, GSTR-3B is due on 20 September. The advance tax second instalment — 45% of estimated annual liability, cumulative — is due on 15 September. The TDS deposit for August deductions is due on 7 September. If your business falls under all three, you have a significant cash flow obligation in a single fortnight.

This blog gives you every deadline for September 2026, explains what each involves, and gives you the penalty calculation for any you miss — so you can prioritize correctly and avoid paying a rupee more than you owe.

All September 2026 Compliance Deadlines at a Glance

This is your complete compliance calendar for September 2026. Dates shaded in blue are GST deadlines; those in green are income tax and TDS deadlines.

TDS Compliance in September 2026

TDS Deposit — 7 September 2026

Any TDS deducted from payments made in August 2026 must be deposited with the government by 7 September 2026. This applies to salary TDS (deducted monthly from employee salaries), TDS on contractor payments, professional fees, rent, interest, commission, and any other payment where TDS is applicable under the Income Tax Act, 2025.

Governing law: Since all August 2026 payments occur after 1 April 2026, TDS is now governed by Section 393 of the Income Tax Act, 2025 (not Sections 194C, 194J, 194H etc. of the old Act). When depositing TDS, ensure your challan quotes the correct new section reference. Portal validation may fail if old Act section numbers are used for post-March 2026 transactions.

Advance Tax: The 15 September Deadline Explained

The 15 September deadline is the second of four advance tax installments for FY 2026-27. It is also the most misunderstood — because the percentage required is cumulative, not just for the quarter.

What ‘cumulative 45%’ means in practice: If your estimated annual tax liability is ₹3 lakh, you must have paid a total of ₹1,35,000 by 15 September — including whatever you paid on 15 June. If you paid ₹30,000 in June (10% — below the required 15%), you need to pay at least ₹1,05,000 in September to reach the 45% cumulative threshold. The shortfall from June also attracts interest.

Who is exempt from advance tax:

• Senior citizens (above 60 years) with no business or professional income — fully exempt from advance tax
• Presumptive taxation taxpayers under Section 44AD and 44ADA (small businesses and professionals with turnover/receipts below the prescribed limits) — can pay 100% of advance tax as a single instalment by 15 March 2027
• Salaried individuals whose entire tax liability is covered by employer TDS — no advance tax required

GST Filing Deadlines in September 2026

GSTR-1: Outward Supply Return — 11 September 2026

Monthly GST filers must report all B2B and B2C invoices issued in August 2026 by 11 September. With GSTR-3B hard-locked since July 2025, GSTR-1 accuracy is more important than ever — errors cannot be corrected directly in GSTR-3B and must go through GSTR-1A before GSTR-3B is filed.

• Critical for September specifically: Any FY 2025-26 invoice that has not yet been reported or was reported with errors must be amended in September’s GSTR-1 (Table 9A). The November 2025 amendment cut-off has passed — September is the last practical window to capture FY 2025-26 output corrections before year-end.
• QRMP filers: September is the last month of Q2 (July–September). Your quarterly GSTR-1 for Q2 is not due until 13 October 2026. However, if you have B2B buyers whose ITC depends on seeing your August invoices in their September GSTR-2B, use the Invoice Furnishing Facility (IFF) before 13 September to upload those invoices for the month.

GSTR-3B: Summary Return + Tax Payment — 20 September 2026

GSTR-3B for August 2026 is due 20 September for monthly filers. This is simultaneously the most important deadline this month and the one with the most cash flow impact — particularly for businesses that also owe advance tax by 15 September.

• September-specific cash flow alert: If you owe both advance tax (15 Sep) and GSTR-3B tax payment (20 Sep), plan your liquidity carefully. Both are cash outflows within 5 days of each other. For a business with ₹50 lakh monthly GST turnover, the GSTR-3B net tax payment alone can be ₹3–8 lakh. Add the advance tax instalment and the combined cash requirement in one fortnight is material.

PMT-06: Monthly GST Payment for QRMP Taxpayers — 25 September 2026

QRMP taxpayers file GST returns quarterly but pay tax monthly. The August 2026 tax payment via Form PMT-06 is due by 25 September. The amount can be calculated using either the Fixed Sum Method (35% of previous quarter’s GSTR-3B tax) or the Self-Assessment Method (based on actual August ITC and liability). If August was a high-revenue month compared to last quarter, the Fixed Sum Method may underpay — use the Self-Assessment Method for accuracy.

Tax Audit Report Deadline — 30 September 2026

Businesses and professionals whose books are required to be audited under Section 44AB must have their Chartered Accountant sign and upload the tax audit report (Form 3CD/3CA/3CB) by 30 September 2026. The ITR filing deadline for audit cases is 31 October 2026 — which is directly dependent on the audit report being completed first.

Who this applies to:

Businesses with turnover above ₹1 crore (₹10 crore if cash transactions are below 5%), and professionals with gross receipts above ₹50 lakh (₹75 lakh under presumptive scheme). Directors of private limited companies and partners of auditable firms also need to ensure the entity-level audit is complete before their personal ITR deadline.

What Each Missed Deadline Costs You: September Edition

September’s deadlines are more expensive to miss than most months — because three of them carry compounding consequences.

Planning Your September Cash Flow: The Fortnight That Matters

For any SME owner juggling GST, TDS, and advance tax simultaneously, September requires deliberate cash flow planning. Here is the sequence of outflows and what to prepare:

September Has Three Deadlines in One Fortnight. Let’s Make Sure You Hit All of Them.

Related Reading

→ July 2026 GST & TDS Due Dates: Don’t Miss These Compliance Deadlines

→ Advance Tax September 15 Deadline: How to Calculate & Pay Correctly

→ Quarterly Review: How to Reconcile GST & Books Before Q2 Ends

→ 10 Signs Your Growing Business Needs a Virtual CFO Right Now

The post September 2026 GST, TDS & Advance Tax Calendar: What You Need to Know for Simple Filing first appeared on CPC Services Pvt. Ltd..

Key Due Dates Businesses Must Remember

For every Indian business, GST compliance is non-negotiable. Missing a deadline doesn’t just mean a late fee — it can block Input Tax Credit (ITC) for your customers, disrupt cash flow, and even invite compliance notices.

According to GSTN data, over 1.4 crore taxpayers are registered under GST, and nearly 12–15% of returns are delayed every month — mostly due to last-minute filing or reconciliation errors.

October 2025 is a critical month. With the festive season driving sales and operations, many businesses tend to overlook filing schedules. This blog provides a complete GST calendar for October 2025, explains why these filings matter, and shares a compliance checklist to help you stay penalty-free.

GST Filing Deadlines in October 2025

Here’s your GST compliance calendar:

Pro Tip :
Mark these dates in your compliance calendar or use accounting software with GST reminders. Even a 1-day delay may cost ₹50/day (₹20 for nil returns) plus 18% annual interest.

Why These Deadlines Matter

• GSTR-1 & IFF → Critical for ITC claims of your customers. If you delay, your buyers cannot claim credit — which strains relationships.
  
• GSTR-3B → The backbone of GST compliance, summarizing sales, purchases, ITC, and liabilities. Any mismatch triggers notices under GST Section 61.
  
• GSTR-7 & GSTR-8 → Directly impact vendors and e-commerce sellers. Late filing blocks their ITC and causes reconciliation delays.

Did you know?
Over 25% of GST mismatches in India arise because vendors file GSTR-1 late. That’s why proactive reconciliation is crucial.

Compliance Checklist for October 2025

Stay penalty-free with this 5-step routine:

• Reconcile Books → Match GSTR-2B with purchase register before filing.
• Verify ITC → Claim only eligible credits (avoid blocked credits under Rule 36).
• Cross-Check Vendor Data → Ensure suppliers file GSTR-1/IFF timely.
• Plan Cash Flow → Keep GST liability funds ready by the 15th of the month.
• File Early → Avoid last-day portal glitches; traffic spikes on¹ 19th–20th.

Common Mistakes Businesses Make

• Filing GSTR-3B without ITC reconciliation → leads to mismatches.
• Ignoring IFF in QRMP → delays buyer’s ITC.
• Forgetting GSTR-7/8 → vendors lose temporary ITC access.
• Waiting till deadline → GST portal crashes cause failed filings.

Pro Tip:
Even filing a nil return on time builds a clean compliance record.

Impact of Missing October GST Deadlines

If you miss your filing schedule:

• Late Fee: ₹50/day (₹20 for nil returns).
• Interest: 18% per annum on unpaid taxes.
• Blocked ITC: Your customers cannot claim credit — impacting your credibility.
• Scrutiny Notices: Repeated delays may lead to GST audit or DRC-01 notices.

GST Compliance Made Simple

Managing multiple returns across states, vendors, and invoices can overwhelm SMEs and startups. That’s why many rely on professional GST consultants.

At CPC Services Pvt. Ltd., we help businesses with:

• Timely GST return filing (monthly & quarterly)
• ITC reconciliation and vendor compliance tracking
• Automated compliance calendars
• Advisory on tax planning, audits, and notices

Need expert GST support this October?

Contact us today for a free consultation.

October 2025 brings a packed GST calendar — GSTR-1, 3B, 7, 8, and IFF all due within weeks. For businesses, timely filing isn’t just a legal mandate — it’s an investment in credibility, cash flow, and growth.

About CPC Services Pvt. Ltd.

CPC Services Pvt. Ltd. is a trusted financial and tax consultancy firm based in Faridabad, Haryana, serving businesses, e-commerce sellers, startups, and professionals across India. With decades of experience, our team of Chartered Accountants, GST experts, and financial advisors provides end-to-end solutions in GST compliance, return filing, ITC reconciliation, tax planning, and business advisory.

We help organizations stay compliant, avoid penalties, and streamline tax operations, ensuring smooth cash flow and credible business practices.

You can reach us via email at 📧 info@cpcservices.co.in or by phone at 📞 +91-9910278975. 

Optimize Your GST Compliance Today:

Whether it’s GSTR-1, GSTR-3B, GSTR-7, GSTR-8, or IFF filings for October 2025, our experts ensure timely and accurate submission, so your business stays penalty-free and ITC claims remain intact.

The post All You Need to Know: GST Filing & Important Deadlines – Oct 2025 first appeared on CPC Services Pvt. Ltd..