Old vs New Income Tax Regime: 7 Costly Mistakes to Avoid in FY 2026-27

Old vs New Income Tax Regime FY 2026-27: 7 Costly Mistakes Taxpayers Must Avoid

From April 1, 2026, the Income Tax Act 2025 replaced the Income Tax Act 1961. While the tax slabs and rates remain unchanged, the structural changes have renewed the debate on regime selection for every taxpayer.

This article identifies the seven most common and costly mistakes taxpayers make when choosing between the old and new regimes, with fully verified worked examples and practical guidance for FY 2026-27.

Quick Reference: Tax Slabs FY 2026-27

New Regime

Standard deduction: Rs. 75,000 Section 87A rebate: Zero tax if taxable income is up to Rs. 12,00,000

Old Regime

Standard deduction: Rs. 50,000 Section 87A rebate: Zero tax if taxable income is up to Rs. 5,00,000

Mistake 1: Assuming the New Regime is Always Better

The most widespread mistake among salaried taxpayers in FY 2026-27 is assuming that because the new regime has lower slab rates, it is always the better choice. This ignores the deduction architecture of the old regime entirely.

Worked Example: Rs. 15 lakh gross salary

Tax Calculation: Old Regime on Rs. 8,25,000

• 0 to Rs. 2,50,000 = Nil
• Rs. 2,50,001 to Rs. 5,00,000 at 5% = Rs. 12,500
• Rs. 5,00,001 to Rs. 8,25,000 at 20% = Rs. 65,000
• Total tax = Rs. 77,500
• Add 4% cess = Rs. 3,100
• Total tax payable = Rs. 80,600

Tax Calculation: New Regime on Rs. 14,25,000

• 0 to Rs. 4,00,000 = Nil
• Rs. 4,00,001 to Rs. 8,00,000 at 5% = Rs. 20,000
• Rs. 8,00,001 to Rs. 12,00,000 at 10% = Rs. 40,000
• Rs. 12,00,001 to Rs. 14,25,000 at 15% = Rs. 33,750
• Total tax = Rs. 93,750
• Add 4% cess = Rs. 3,750
• Total tax payable = Rs. 97,500

At Rs. 15 lakh gross salary with full deductions, the old regime (Rs. 80,600) saves Rs. 16,900 compared to the new regime (Rs. 97,500). This is exactly the mistake many taxpayers make – assuming the new regime is always better without running the actual numbers.

When the new regime is clearly better: For taxpayers with gross salary up to Rs. 12,75,000, taxable income under new regime is Rs. 12,00,000 after standard deduction. Section 87A rebate applies and tax is zero. This is the clearest win for the new regime regardless of investment habits.

Mistake 2: Not Calculating Both Regimes Before Deciding

Many taxpayers rely on a colleague’s advice or a simplified comparison chart to make their regime decision. The correct approach is to calculate actual tax liability under both regimes using their specific salary structure.

Critical variables that determine the better regime:

• Basic salary as a percentage of CTC (affects HRA and EPF)
• City of residence (from FY 2026-27, eight cities qualify for 50% HRA: Delhi, Mumbai, Chennai, Kolkata, Bangalore, Hyderabad, Pune, and Ahmedabad)
• Actual rent paid relative to salary
• Home loan outstanding and annual interest
• Insurance premium amounts
• NPS contribution structure

Two colleagues earning identical gross salaries in the same city can arrive at different optimal regimes. Regime selection must be individualised.

Mistake 3: Ignoring the Deadline for Regime Choice

Under the Income Tax Act 2025, the regime choice for salaried taxpayers is made at the time of ITR filing. However, for TDS purposes, the taxpayer must communicate their regime preference to their employer at the beginning of the financial year through Form 124 (which replaced Form 12BB from April 2026).

Critical rule that most taxpayers miss: If a salaried taxpayer does not file their ITR by July 31, 2026, they lose the right to choose the old tax regime for FY 2026-27. The new regime becomes mandatory for belated returns filed after July 31, 2026.

Practical implication: Ensure all clients who benefit from the old regime file their ITR by July 31, 2026. This deadline is not negotiable for regime selection purposes.

Mistake 4: Forgetting Employer NPS Deduction Available in New Regime

Under Section 80CCD(2) (now Section 125 of the Income Tax Act 2025), employer NPS contribution up to 14% of basic salary is fully deductible even under the new tax regime.

Worked Example

This deduction requires no additional out-of-pocket investment. Taxpayers should request their employer to restructure CTC to include this component.

Mistake 5: Assuming HRA Cannot Be Claimed After April 2026

HRA exemption under Section 10(13A) continues unchanged under the old regime. The formula remains the same: minimum of actual HRA received, rent paid minus 10% of salary, or 50%/40% of salary depending on city.

What changed from April 2026: The city classification for 50% HRA expanded from 4 cities to 8 cities. Bangalore, Hyderabad, Pune, and Ahmedabad now qualify for 50% of basic salary from FY 2026-27 onwards.

What did not change:

• HRA exemption formula
• Requirement to pay rent and maintain receipts
• PAN of landlord for rent above Rs. 1,00,000 per year
• HRA is available only under old regime

Mistake 6: Locking into the Wrong Regime for Business Income Earners

For taxpayers with business or professional income, the regime choice works differently.

Salaried taxpayers: Can switch between old and new regime every year at ITR filing.

Business income taxpayers: Can switch from new to old regime only once in a lifetime. Once they switch back to old regime, they cannot return to new regime again.

Practical guidance: For self-employed professionals, freelancers, and business owners, the regime choice must be evaluated not just for the current year but projected over 3 to 5 years.

Mistake 7: Not Informing Employer of Regime Choice on Time

TDS on salary is computed based on the regime communicated to the employer through Form 124. If the taxpayer fails to inform the employer, the employer defaults to the new regime.

If the taxpayer later files under old regime, they may face a large tax payment at filing time along with interest under Section 234B.

Practical steps:

• Submit Form 124 to employer in April 2026 with regime preference clearly marked
• Verify April 2026 salary slip to confirm TDS is computed under correct regime
• If switching regime mid-year, inform employer immediately

Key Differences: Old vs New Regime

Tax Liability Comparison at Key Income Levels

Assumptions for old regime calculations: Full utilisation of Section 80C (Rs. 1,50,000), Section 80D (Rs. 25,000), HRA (Rs. 2,50,000), home loan interest (Rs. 2,00,000). All figures include 4% cess. Actual savings will vary based on individual deduction utilisation.

Important note for Rs. 10,00,000 row: Under new regime, taxable income is Rs. 9,25,000 which is below Rs. 12,00,000. Section 87A rebate applies and tax is zero. Both regimes result in zero tax at this income level when full deductions are claimed under old regime.

Important note for Rs. 20,00,000 row: Even with full deductions under old regime, new regime results in lower tax at this income level. Old regime becomes better here only when additional deductions beyond those assumed are available.

Verified Tax Calculation: Rs. 15,00,000 Gross Salary

Old Regime

Taxable income after deductions = Rs. 8,25,000

• 0 to Rs. 2,50,000 = Nil
• Rs. 2,50,001 to Rs. 5,00,000 at 5% = Rs. 12,500
• Rs. 5,00,001 to Rs. 8,25,000 at 20% = Rs. 65,000
• Total tax = Rs. 77,500
• Add 4% cess = Rs. 3,100
• Total = Rs. 80,600

New Regime

Taxable income = Rs. 14,25,000

• 0 to Rs. 4,00,000 = Nil
• Rs. 4,00,001 to Rs. 8,00,000 at 5% = Rs. 20,000
• Rs. 8,00,001 to Rs. 12,00,000 at 10% = Rs. 40,000
• Rs. 12,00,001 to Rs. 14,25,000 at 15% = Rs. 33,750
• Total tax = Rs. 93,750
• Add 4% cess = Rs. 3,750
• Total = Rs. 97,500

Old regime saves Rs. 16,900 at Rs. 15,00,000 gross salary when full deductions are claimed.

Verified Tax Calculation: Rs. 20,00,000 Gross Salary

Old Regime

Taxable income after deductions = Rs. 13,25,000

• 0 to Rs. 2,50,000 = Nil
• Rs. 2,50,001 to Rs. 5,00,000 at 5% = Rs. 12,500
• Rs. 5,00,001 to Rs. 10,00,000 at 20% = Rs. 1,00,000
• Rs. 10,00,001 to Rs. 13,25,000 at 30% = Rs. 97,500
• Total tax = Rs. 2,10,000
• Add 4% cess = Rs. 8,400
• Total = Rs. 2,18,400

New Regime

Taxable income = Rs. 19,25,000

• 0 to Rs. 4,00,000 = Nil
• Rs. 4,00,001 to Rs. 8,00,000 at 5% = Rs. 20,000
• Rs. 8,00,001 to Rs. 12,00,000 at 10% = Rs. 40,000
• Rs. 12,00,001 to Rs. 16,00,000 at 15% = Rs. 60,000
• Rs. 16,00,001 to Rs. 19,25,000 at 20% = Rs. 65,000
• Total tax = Rs. 1,85,000
• Add 4% cess = Rs. 7,400
• Total = Rs. 1,92,400

New regime saves Rs. 26,000 at Rs. 20,00,000 gross salary even when full deductions are claimed under old regime.

Conclusion

The old vs new regime decision in FY 2026-27 is not a one-size-fits-all calculation. Key takeaways:

• For gross salary up to Rs. 12,75,000: Both regimes result in zero tax. New regime is simpler.
• For gross salary of Rs. 15,00,000 with full deductions: Old regime saves Rs. 16,900.
• For gross salary of Rs. 20,00,000 even with full deductions: New regime saves Rs. 26,000.
• For higher incomes with very large deductions: Old regime may still be better. Individual calculation is essential.

The seven mistakes outlined above cost taxpayers significantly. Not because the wrong regime was chosen, but because the choice was made without adequate calculation, without meeting deadlines, or without structuring salary components optimally.

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Disclaimer: This article is for informational purposes only and does not constitute tax advice. Tax laws are subject to change. Consult a qualified tax professional before making financial decisions.

About the Author: Diksha Chawla is the Founder of FinLecture (finlecture.in), a financial education platform helping salaried professionals, freelancers, and small business owners understand income tax and personal finance in India. She holds an MBA in Finance with 7 years of experience in taxation education.

(Republished with Amendments)