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. For a salaried professional earning Rs. 20 lakh annually, choosing the wrong regime can cost up to Rs. 1,25,000 in additional tax outgo every year.

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

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 assumption ignores the deduction architecture of the old regime entirely.

Worked Example: Rs. 20 lakh salary

For this taxpayer, the old regime saves Rs. 1,25,000 annually. The new regime’s lower slab rates do not compensate for the loss of deductions at this income level.

When the new regime is genuinely better: For taxpayers with income up to Rs. 12,75,000 (gross salary including standard deduction), the new regime results in zero tax due to the Section 87A rebate of Rs. 60,000. At this income level, the new regime is clearly superior 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, deductions, and exemptions.

Critical variables that determine the better regime:

• Basic salary as a percentage of CTC (affects HRA and EPF calculations)
• City of residence (metro vs non-metro for HRA — 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 outgo
• Insurance premium amounts
• NPS contribution structure

Two colleagues earning identical gross salaries in the same city can arrive at different optimal regimes based on these variables. 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 throughout the year, 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 salaried taxpayers miss:

If a salaried taxpayer does not file their ITR by the original deadline of 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.

This means a taxpayer who was better off under the old regime by Rs. 1,25,000, and who misses the July 31 deadline, permanently loses that benefit for the year. No revised return or belated return can restore the regime choice.

Practical implication for tax professionals: 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

The most commonly overlooked advantage available in the new regime is the employer contribution to the National Pension System (NPS).

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. This deduction is not available to employees who do not have this structured into their CTC.

Worked Example:

This deduction requires no additional out-of-pocket investment by the employee. It is a restructuring of the existing CTC. Taxpayers who have not yet requested their employer to include this component should do so at the start of FY 2026-27.

Mistake 5: Assuming HRA Cannot Be Claimed After April 2026

A significant misconception has emerged following the introduction of the Income Tax Act 2025 – that HRA exemption has been removed or modified substantially.

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

What did change from April 2026:

The city classification for the 50% HRA exemption expanded from 4 cities to 8 cities. Bangalore, Hyderabad, Pune, and Ahmedabad now qualify for 50% of basic salary (Condition 3) from FY 2026-27 onwards.

What did not change:

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

Taxpayers in the four newly added cities who were previously capped at 40% should verify whether the 50% classification changes their regime decision for FY 2026-27.

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

For taxpayers with business or professional income, the regime choice works differently and the stakes are significantly higher.

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

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

This asymmetry means that a business income taxpayer who hastily chooses the new regime in FY 2026-27 and later realises the old regime would have been better, has permanently lost future flexibility.

Practical guidance for tax professionals: 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 based on expected income trajectory and deduction utilisation.

Mistake 7: Not Informing Employer of Regime Choice on Time

Many salaried taxpayers are unaware that TDS on salary throughout the year is computed based on the regime they communicate to their employer at the beginning of the financial year through Form 124.

If a taxpayer fails to inform the employer, the employer defaults to the new regime (which is the default regime from FY 2023-24 onwards) and computes TDS accordingly. If the taxpayer later decides to file under the old regime, they will have had insufficient TDS deducted and may face a large tax payment at the time of filing along with interest under Section 234B.

Practical steps:

• Submit Form 124 to employer at the start of April 2026 with regime preference clearly marked
• If switching from new to old regime, ensure employer adjusts TDS from the next payroll cycle
• Verify April 2026 salary slip to confirm TDS is being computed under the correct regime

Key Differences: Old vs New Regime at a Glance

Tax Liability Comparison at Key Income Levels

Note: Old regime calculations assume full utilisation of Section 80C (Rs. 1,50,000), Section 80D (Rs. 25,000), HRA (Rs. 2,50,000), and home loan interest (Rs. 2,00,000). Actual savings will vary based on individual deduction utilisation.

Conclusion

The old vs new regime decision in FY 2026-27 is not a one-size-fits-all calculation. It depends on income level, actual deduction utilisation, city of residence, and financial behaviour.

For taxpayers earning below Rs. 12,75,000 without significant deductions, the new regime is clearly superior. For taxpayers earning above Rs. 15,00,000 who actively utilise home loan, HRA, Section 80C, and health insurance deductions, the old regime typically delivers better outcomes.

The seven mistakes outlined above cost taxpayers thousands to lakhs of rupees annually — 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.

Tax professionals advising clients should ensure that regime selection is reviewed at the start of every financial year with updated numbers, and that employer communication is completed before the first payroll of April.

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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.