Most taxpayers do not lose money on their tax return because of a complicated legal point. They lose it because of an ordinary slip: a wrong form, a forgotten interest credit, an unverified submission or a deduction claimed in the wrong regime. For AY 2026-27, which reports income earned in FY 2025-26, such slips are easier to make than usual, because the return forms changed in several ways and the department now pre-fills far more data from banks, brokers, employers and registrars. The regular July deadline for most individuals has passed, so anyone who has not yet filed is working with a belated return, which can be filed until 31 December 2026 with a late fee and interest.
This guide from The Classic Partners LLP, a chartered accountancy firm in Andheri East, Mumbai, lists the ten ITR filing mistakes for AY 2026-27 that we see most often in our practice, explains why each one matters, and tells you how to avoid it. It also covers the new form changes that trip up even experienced filers, how to check your return before you submit it, and what to do if an error has already gone through.
Why Do Small ITR Errors Create Big Problems in AY 2026–27?
Small ITR errors create big problems because the Income Tax Department now compares your return with data it already holds, so an omission or mismatch is detected automatically and can lead to an adjusted intimation, a defective-return notice or a delayed refund.
Three features of this year raise the stakes:
- Third-party data is pre-filled. The department's Annual Information Statement lists interest, dividends, securities trades, mutual fund redemptions, property deals and other items reported by third parties.
- The new regime is the default. Filing without a deliberate choice can quietly remove deductions you were counting on.
- Most deadlines have passed. Any error found now is fixed through a belated, revised or updated return, each of which carries its own cost and limits.
A short, careful review before submission is far cheaper than any of these remedies. If you are unsure where to start, our ITR filing services and tax health check can help.
What Are the 10 Costliest ITR Filing Errors This Year?
The ten costliest errors are filing the wrong form, ignoring the AIS, omitting income, mishandling the tax regime, claiming deductions without support, misreporting capital gains and F&O trading, missing foreign or rental disclosures, giving wrong bank details, skipping e-verification and filing late without a plan. Each is described below with its fix.
Using the Wrong ITR Form
Each form has strict conditions. A salaried person with foreign assets, a company directorship or large gains cannot use ITR-1, and a trader in futures and options needs ITR-3. Read the eligibility notes on the portal before you start. Our pages on ITR-1, ITR-2, ITR-3 and ITR-4 explain who qualifies.
Filing Without the AIS
Download the Annual Information Statement, the Taxpayer Information Summary and Form 26AS, and compare them with your own records. Where an entry is wrong, give feedback on the portal. Where it is right, make sure your return agrees with it.
Forgetting Small Income Streams
Savings interest, fixed deposit interest, dividends, rent, freelance receipts and gains on mutual funds are taxable even when no tax was deducted. Exempt income should still be reported in the exempt-income schedule.
Letting the Default Regime Decide
The new regime applies unless you opt out, and the cheaper option changes with your income and investments. Salaried taxpayers can choose each year, while those with business income need Form 10-IEA to leave the new regime. Our guide to new regime vs old regime for AY 2026-27 shows the break-even deductions at each salary.
Claiming Deductions Without Proof
Sections 80C, 80D, HRA and home loan interest on a self-occupied property are generally old-regime benefits. Claim them only where allowed and keep receipts, certificates and the landlord's details ready.
Misreporting Capital Gains and F&O
Mix-ups between short-term and long-term gains, wrong dates or missed switches are common. Traders must now show F&O turnover and profit separately in ITR-3. Use broker and registrar statements and see our capital gain overview and guide to filing ITR for cryptocurrency.
Missing Rental and Foreign Disclosures
For AY 2026-27, house property reporting asks for tenant details and unrealised rent, and foreign assets, foreign income and overseas retirement accounts must be reported in the proper schedules. Gaps here can attract penalties under the Black Money Act in serious cases.
Wrong or Unvalidated Bank Details
A refund goes only to a pre-validated account linked to your PAN. A closed account, a typing error or a name mismatch can hold the refund up for weeks, so validate the account before you file.
Not E-Verifying
A return is complete only after verification, and the current window is 30 days from filing. An unverified return is treated as not filed, which can bring the late fee and loss of carry-forward of losses.
Filing Late Without a Plan
A belated return attracts a fee under section 234F of ₹5,000, or ₹1,000 where income is up to ₹5 lakh, plus interest under section 234A on unpaid tax, and business and capital losses generally cannot be carried forward. File as early as possible and pay any tax due first.
What Do the New AY 2026–27 Form Changes Mean for Your Return?
The new forms change who can use the simple returns and what extra details must be shown, so a return prepared on last year's habits can be wrong in small but important ways. The key changes reported for AY 2026-27 are worth knowing before you file.
| Form | What changed | What it means for you |
|---|---|---|
| ITR-1 and ITR-4 | Income from up to two house properties is allowed, and long-term gains under section 112A up to ₹1.25 lakh can be reported when there are no carried-forward losses | More taxpayers with modest gains can stay on the simple forms |
| ITR-1 and ITR-4 | Section 89A reporting for foreign retirement accounts has been removed | People with such income move to ITR-2 or ITR-3 |
| ITR-3 | Separate reporting of futures and options turnover and results | F&O turnover and profit or loss must be shown on their own |
| ITR-2 and ITR-3 | Capital gains schedules reflect the rates that apply to transfers on or after 23 July 2024 | Dates of transfer decide the rate, so check each one |
| All forms | Secondary contact details added | Keep a second phone number or email ready |
Because utilities are updated through the season, read the instructions to the form you are using and see our page on the new income tax forms for 2026 for a fuller summary.
How Can You Catch Errors Before You Submit the Return?
You can catch most errors by checking your documents against the portal's statements, testing both tax regimes, reviewing the pre-filled data line by line and reading the computation sheet before submitting. This takes less time than responding to a notice. Follow the six steps below in order.
- Compare Your StatementsCompare salary in Form 16 with the AIS, check each TDS credit in Form 26AS and look for interest or dividend entries you did not expect.
- Work Out Tax Under Both RegimesCompute tax under the new and the old regime and note the difference before you choose.
- Review the Pre-Filled DataReview the pre-filled personal, bank and income details instead of accepting them blindly.
- Back Every Deduction With a DocumentCheck that every deduction you claim has a document behind it.
- Pay Any Balance TaxPay any balance tax before you submit the return.
- File and E-Verify ImmediatelySubmit the return and e-verify it straight away, because an unverified return is treated as not filed.
A second pair of eyes helps, particularly for traders, investors and anyone with income from abroad, and our team can review your computation before you submit. For notices that arrive after filing, see our support for defective return notices under section 139(9) and notice reply and assessment support.
📋 Note: Download the AIS again on the day you file. New entries can be added late in the season, and a short final check can catch an interest credit or a redemption that appeared after your first download.
What Can You Do If You Have Already Filed With a Mistake?
If you have already filed with a mistake, the usual remedy is a revised return, and if that window has closed, an updated return with additional tax. A reply to a defective-return notice is a separate route and has its own time limit.
| Situation | Route | Key point |
|---|---|---|
| You missed the regular due date | Belated return | Can be filed until 31 December 2026, with a section 234F fee and section 234A interest |
| You filed with an omission or wrong entry | Revised return | Replaces the original; reported to be available until 31 March 2027, with a fee for returns filed after 31 December 2026. Check the portal for the date that applies to you |
| You received a defective-return notice | Reply to the notice | Respond within the time given, which is a separate limit from the revised-return window |
| The other windows have closed | Updated return (ITR-U) under section 139(8A) | Allows voluntary correction for a longer period with additional tax, which rises the later you file. It cannot be used for every purpose, such as claiming a refund or reducing tax |
Do not delay once you notice an error, because the additional tax on an updated return rises the later you file.
⚠️ Important: Do not file a second fresh return in a different form to fix a mistake. Duplicate returns for the same year create confusion. Use the revised return, defective-return response or updated return route that the law provides for your situation.
How Has Return Filing Evolved, and Why Are Errors Easier to Spot Now?
Return filing has evolved from paper forms before 1991 to a data-matched online system, which is why errors that once passed unnoticed are now flagged quickly.
- Before 1991. Taxpayers filed paper returns under the Income-tax Act, 1961 and the department had limited independent data.
- After liberalisation. PAN-based systems and TDS reporting expanded, and Form 26AS gathered tax credits in one place.
- Early 2000s. Electronic filing began.
- Recent years. The portal added pre-filled returns, the Annual Information Statement and faceless processes.
- 1 April 2026. The Income-tax Act, 2025 applies from this date, but returns for AY 2026-27 continue under the 1961 Act. Forms, utilities and due dates are published on the official Income Tax Department e-filing portal.
Want a Second Opinion Before You File?
A short review of your computation can catch wrong forms, mismatches and regime errors before they become notices. The Classic Partners LLP helps individuals, traders, NRIs and businesses with accurate return preparation and filing through our income tax e-filing practice.
Phone: +91 98190 00445 or +91 98190 00511 · Email: info@theclassicpartners.com · Contact page
Frequently Asked Questions About ITR Filing Mistakes in AY 2026–27
What is the most common mistake in ITR filing?
The most common mistakes are choosing the wrong ITR form and filing without checking the AIS. Both lead to defective-return notices or mismatch adjustments. Check form eligibility on the portal and reconcile your return with the AIS, TIS and Form 26AS before you submit.
Can I still file my ITR for AY 2026–27?
Yes. If you missed the regular due date, you can file a belated return until 31 December 2026, with a late fee under section 234F and interest under section 234A. Filing late can also stop you from carrying forward certain losses, so file as early as possible.
What happens if I do not e-verify my return?
An unverified return is treated as not filed. The portal currently allows 30 days from filing to verify it. If you miss the window, you may have to request condonation or file again as a belated return, with the late fee and interest that follow.
Which ITR form should a trader in futures and options use?
A trader with F&O income files ITR-3, which now has separate fields for F&O turnover and profit or loss. Presumptive taxation forms are generally not suitable for such trading, so check eligibility before filing.
Can I claim 80C and HRA under the new tax regime?
Generally no. Section 80C, 80D, HRA and home loan interest on a self-occupied property are old-regime benefits. Compare both regimes before you file, because the cheaper option varies with your income and deductions.
How do I correct a mistake after filing my ITR?
File a revised return if the window is still open for AY 2026-27, or respond to a defective-return notice within the time given. If neither is possible, an updated return under section 139(8A) may be available with additional tax. Confirm the current conditions on the portal.
