A step-by-step guide for salaried employees, freelancers, business owners, and SME directors — calculate your Q2 advance tax instalment accurately and pay before the deadline to avoid compounding interest.

Most taxpayers in India know about the September 15 advance tax deadline. Far fewer know exactly how to calculate the correct amount — or understand why getting it wrong in September is more expensive than missing any other instalment during the year.

The second advance tax instalment requires a cumulative payment of 45% of your estimated annual tax by 15 September. That means it is not just the tax on Q2 income. It accounts for Q1 income too, less whatever you paid in June. If you underpaid in June, September catches that up — with interest running from June 15, not from September 15.

This guide gives you the calculation framework, three worked examples by taxpayer type, the exact payment steps on the Income Tax portal, and the interest calculation for anyone who has already missed the June instalment.

Who Must Pay Advance Tax?

Advance tax applies broadly — not just to business owners. Here is the complete picture:

You must pay advance tax if:

• Your estimated total income tax for FY 2026-27 exceeds ₹10,000 after TDS. This includes TDS deducted by your employer, banks, tenants, and any other deductors.
• You have income that is not covered by TDS — rental income, business profit, freelance income, FD interest, dividend income, or capital gains.
• You are a salaried employee who switched jobs during the year and the new employer is not accounting for the previous employer’s TDS.
• You have made capital gains in FY 2026-27 that were not anticipated when June’s advance tax was paid.

You are exempt from advance tax if:

• You are a senior citizen (60 years or above) with no income from business or profession — fully exempt regardless of income level.
• You are a small business or professional under presumptive taxation (Section 44AD or 44ADA). You can pay 100% of advance tax as a single instalment by 15 March 2027. No quarterly payments required.
• Your entire tax liability is covered by employer TDS. If TDS deducted by your employer equals or exceeds your full tax, no separate advance tax payment is needed.

The Four-Instalment Schedule for FY 2026-27

Advance tax is paid in four cumulative instalments. The percentages are cumulative — each instalment includes the total paid so far, not just the current quarter’s share.

How to Calculate Your September 15 Advance Tax Payment

Follow these six steps to calculate exactly how much to pay by 15 September 2026.

1. Estimate your total income for FY 2026-27

Add up all income you expect to earn between April 2026 and March 2027:

• Salary: Your expected gross salary for the full year (not just April–September)
• Business/professional income: Estimated net profit for the full year based on Q1 actual and projected Q2–Q4
• Rental income: Annual rental receipts, net of municipal taxes paid
• Capital gains: Any gains already realized (shares, mutual funds, property) plus any anticipated before March 2027
• Interest income: FD interest, savings account interest, bond interest for the full year

2. Deduct eligible deductions and exemptions

Under whichever regime you have chosen for FY 2026-27:

New regime: Deduct ₹75,000 standard deduction (salaried), employer NPS contribution (Section 80CCD(2)), and any other specific exemptions available under the new regime.

Old regime: Deduct all eligible amounts — 80C (up to ₹1.5 lakh), 80D, HRA exemption, home loan interest (Section 24b, up to ₹2 lakh for self-occupied), NPS (80CCD(1B)), and any other applicable deductions.

Compute your taxable income.

3. Calculate the tax on taxable income

Apply the appropriate tax slabs for FY 2026-27 to your estimated taxable income:

New regime slabs: Nil up to ₹4L | 5% on ₹4L–₹8L | 10% on ₹8L–₹12L | 15% on ₹12L–₹16L | 20% on ₹16L–₹20L | 25% on ₹20L–₹24L | 30% above ₹24L

Old regime slabs: Nil up to ₹2.5L | 5% on ₹2.5L–₹5L | 20% on ₹5L–₹10L | 30% above ₹10L

Add 4% health and education cess on the total tax. Add surcharge if income exceeds ₹50 lakh.

4. Subtract TDS already deducted or expected for the full year

TDS is a credit against your advance tax obligation. Deduct:

• Employer TDS: Projected TDS from Form 16 for the full year (ask your employer for the projected TDS figure)
• Bank TDS (Section 194A): TDS on FD interest, typically 10% if PAN is provided
• TDS on rent received (Section 194I): If your tenant deducts TDS on rent paid to you
• TCS received: Any TCS collected by sellers from whom you purchased goods

This gives you your net advance tax liability for the year. If this figure is below ₹10,000, no advance tax is required.

5. Calculate what you must pay by 15 September

Your September payment = 45% of net advance tax liability − what you already paid in June.

Formula: September payment = (Net annual tax liability × 45%) − June payment made

• If you underpaid in June: The shortfall from June also attracts interest from 15 June. You should make up the June shortfall in September to stop the interest from compounding further.
• If you overpaid in June: The excess counts toward the 45% requirement — reduce September payment accordingly. No refund for over payment at instalment stage; excess is adjusted at ITR filing.

6. Pay online via Income Tax e-filing portal

Go to incometax.gov.in → e-File → e-Pay Tax → New Payment → Income Tax. Select:

• Tax Year: 2026-27
• Type of Payment — Minor Head: 100 — Advance Tax
• Assessment Year: 2027-28

Enter the tax amount under the relevant heads (income tax, surcharge if applicable, cess). Choose your payment method (net banking, UPI, debit card, NEFT/RTGS). Download and save the challan immediately after payment — note the CIN (Challan Identification Number). You will need it for ITR filing.

Three Worked Examples: Calculate Your September Payment

Use these examples as templates. Replace the figures with your own estimated income and deductions.

Example 1: Rajan, Salaried Employee with Rental Income — ₹18 lakh salary + ₹4.8 lakh annual rent

Rajan’s total tax is modest because employer TDS covers most of his liability. His September payment is under ₹12,000 — but if he skips it, interest at 1% per month runs on the ₹11,937 shortfall from September 15 onwards.

Example 2: Meera, Freelance Consultant — Estimated ₹28 lakh net professional income

Meera underpaid in June by ₹4,260. That shortfall has been attracting 1% per month interest since 15 June — approximately ₹85 in interest for the June-to-September period. Her September payment of ₹1,02,780 brings her to the 45% cumulative threshold and stops the June shortfall interest from compounding.

Example 3: Ashok, SME Owner — Manufacturing business, estimated ₹50 lakh profit

Ashok’s surcharge (10% on income between ₹50L and ₹1 crore) adds ₹1.08 lakh to his tax. Many business owners miss the surcharge in their advance tax estimate — and then face a ₹10,000+ shortfall interest at year-end. Always check if your income crosses ₹50 lakh, ₹1 crore, or ₹2 crore surcharge thresholds.

Interest Calculation: What It Costs to Underpay

Missing or underpaying the September advance tax instalment triggers interest under Section 234C of the Income Tax Act, 2025 (formerly Section 234C of the old Act). Here is how to calculate it:

Interest Under Section 234C (for Instalment Shortfall)

Formula: Interest = Shortfall from required cumulative amount × 1% × number of months

For the September instalment: If by 15 September you have paid less than 45% of your annual tax, interest runs at 1% per month on the shortfall — for 3 months (from 15 September to 15 December, when the next instalment is due). If the shortfall is still not covered by December, interest continues.

For the June instalment shortfall carried into September: If you underpaid in June, the shortfall attracted interest from 15 June. If you pay the outstanding in September, interest runs for 3 months (June to September). Each month is counted as a full month — even if you pay on 16 September, that is a full additional month.

Already Missed the June Instalment? What to Do Before September 15

If you paid nothing in June — or paid less than 15% — the September instalment is your opportunity to correct the position. Here is the practical approach:

If you paid nothing in June:

You need to catch up to the 45% cumulative threshold by September 15. Pay the full 45% in one payment. Interest under Section 234C for the June shortfall has already accrued for 3 months (June 15 to September 15) — this cannot be avoided. But paying the full 45% now stops further interest from the September instalment.

Interest already owed on June shortfall: 15% of annual tax × 1% × 3 months. For a taxpayer with ₹5 lakh annual tax liability, this is ₹5 lakh × 15% × 1% × 3 = ₹2,250. This interest is not paid separately — it is accounted for when the ITR is filed and assessed.

If you paid some but below the 15% threshold in June:

Interest under 234C runs on the portion of the shortfall only. In September, pay enough to reach the 45% cumulative threshold. The June shortfall interest is calculated and added at assessment time — you do not need to pay it separately now.

5 Common Advance Tax Mistakes — and How to Avoid Them

1. Estimating only April–September income instead of the full year

Advance tax is based on your estimated total income for FY 2026-27 (April 2026 to March 2027). If you estimate only the first half, you understate your liability — and the December and March instalments become very large, or interest under Section 234B accrues at year-end. Always project the full year’s income, even if the second half is uncertain. Use a conservative but realistic estimate.

2. Forgetting to include capital gains in the estimate

Capital gains from selling shares, mutual funds, or property are part of your taxable income and affect advance tax liability. Many taxpayers who sell assets mid-year forget to include the gains in their advance tax estimate. The result: a significant shortfall discovered only at ITR filing time, with Section 234B interest running from April of the assessment year.

3. Not accounting for surcharge at income above ₹50 lakh

The tax calculation seems correct — until income crosses ₹50 lakh and a 10% surcharge applies. For a taxpayer with ₹55 lakh taxable income under the new regime, the surcharge adds approximately ₹30,000–₹35,000 in additional tax. If the advance tax estimate was made without surcharge, the shortfall attracts full Section 234C interest. Always check if your income crosses the ₹50 lakh, ₹1 crore, or ₹2 crore surcharge thresholds.

4. Using old Act section numbers when paying via portal

From FY 2026-27, advance tax payments are governed by the Income Tax Act, 2025. When paying on the portal, select Tax Year 2026-27 (not Assessment Year 2026-27 — that would apply to FY 2025-26 payments). A payment credited to the wrong tax year does not count as advance tax for the current year and creates a mismatch at assessment.

5. Paying on 16 September instead of 15 September

Interest is calculated in full months. If you pay on 16 September 2026 instead of 15 September, the month of September counts as a complete month for Section 234C purposes. For a taxpayer with a ₹2 lakh shortfall, this one-day delay costs ₹2,000 in additional interest. Mark 13 September as your internal deadline — that gives two working days buffer for portal glitches and bank processing.

Pay the Right Amount. Pay on Time. Pay Once.

Related Reading

• September 2026 GST, TDS & Advance Tax Calendar: Filing Made Simple
• New vs Old Tax Regime FY 2026-27: Which One Should You Choose?
• ITR Filing 2026: Step-by-Step Guide + Common Mistakes to Avoid
• 10 Signs Your Growing Business Needs a Virtual CFO Right Now

The post Advance Tax September 15: How to Avoid Common Costly Mistakes 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..