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..

As 2025 draws to a close, December becomes a crucial month for compliance. With multiple GST and TDS deadlines approaching, staying updated helps avoid last-minute rush, penalties, and compliance errors.

Whether you’re a business owner, HR professional, or consultant managing client filings — this guide covers every important due date and checklist you need for December 2025.

Learn more about our end-to-end compliance approach at CPC Services Pvt. Ltd.

Why December Compliance Matters

December isn’t just the final month of the calendar year — it marks the start of fourth-quarter planning for most taxpayers. Timely filings now can help you:

• Maintain a clean compliance record before FY 2025–26 closes with support from our Corporate Compliance Services.
  
• Avoid interest, late fees, or penalties from missed returns through expert Tax Advisory Services.
  
• Prepare smoothly for Q4 audits, reconciliations, and advance tax with professional Audit & Assurance Services.

It’s also a month when many SMEs, startups, and consultants are busy with festive season operations — making it easy to overlook key compliance dates.

Let’s ensure that doesn’t happen this year.

Before filing GSTR-3B, always reconcile Input Tax Credit (ITC) with GSTR-2B to prevent mismatches, cash flow issues, or department notices later. Our Indirect Taxes (GST) Services help ensure accurate reconciliation and filing.

Key TDS & TCS Deadlines in December 2025

Additional Key Direct Tax Compliance Deadlines – December 2025

To help businesses stay fully compliant, here are important deadlines falling in December 2025:

• 10th December 2025 – Extended due date for filing Income Tax Returns for whose accounts require audit with professional Accounting Services.
  
• 15th December 2025 – Due date for payment of the 3rd installment of Advance Tax for FY 2025–26 (AY 2026–27).
  
• 31st December 2025 – Due date for filing pending Income Tax Returns for those who missed earlier deadlines.
  
• 31st December 2025 – Due date for filing Revised Income Tax Returns in case of errors or omissions in earlier filed returns.
  
• 31st December 2025 – Extended due date for submission of e-forms under the Companies Act for FY 2024–25 (year ended 31 March 2025).
  
• 31st December 2025 – Due date for filing GST Annual Returns GSTR-9 (& GSTR-9C (along with GSTR-9 applicable for entities with turnover above ₹5 crore).

Monthly Compliance Checklist – December 2025

Your quick to-do list for a smooth and penalty-free month:

• Reconcile all sales and purchase data on the GST portal with help from GST Compliance Experts.
• Verify TDS deducted and deposited for November transactions.
• Cross-check vendor invoices and input tax credits.
• File any pending GSTR-1 or GSTR-3B from previous months.
• Review advance tax payments due on 15th December (3rd installment).
• Prepare payroll and TDS adjustments before year-end using HR & Payroll Services.

For Businesses & Accounting Teams

December is the perfect time for a mini internal compliance audit.

• Review GST input mismatches and resolve pending notices with Advisory Services.
  
• Verify all e-invoices and e-way bills for accuracy.
  
• Reconcile vendor GSTINs and transactions for year-end filing.

Doing this ensures a seamless transition into Q4, reduces audit stress, and helps maintain strong financial control before the annual return cycle begins — especially for businesses across sectors we serve in Industries Served.

For HR & Payroll Managers

December overlaps key payroll and HR compliance activities. Make sure to:

• Deduct and deposit TDS on salaries, bonuses, and reimbursements accurately.
• Reconcile PF and ESIC filings before the January submission window.
• Prepare salary structures and investment proofs aligned with the new tax regime options for 2026 with expert Payroll Compliance Support.

Proactive payroll and tax alignment in December can save time, penalties, and compliance burden during the financial year-end.

Proactive Compliance = Peace of Mind

Staying updated with monthly deadlines isn’t just about avoiding penalties — it’s about building financial discipline and credibility.

For business owners, it reflects professionalism and investor trust.
For consultants and professionals, it means being audit-ready and stress-free.

If compliance feels overwhelming amid year-end workloads, consider outsourcing your filings.

With CPC Services, you get expert-led, timely, and error-free compliance support — so you can focus on what truly matters: growing your business.

Key Takeaway

December compliance sets the tone for a smooth year-end closure.

Staying ahead of GST and TDS deadlines in December 2025 ensures a penalty-free close to the year and a stronger start to FY 2026.

Need Help with December Filings?

CPC Services Pvt. Ltd. offers complete support in GST, TDS, accounting, payroll, and compliance management — backed by 35+ years of expertise.

Schedule a Free Compliance Consultation today and ensure your December filings are completed on time, every time.

The post Foolproof Checklist Makes December 2025 GST and TDS Easy first appeared on CPC Services Pvt. Ltd..