Income Tax Return Filing 2026: 6 Important Deadlines Every Taxpayer Must Know

As the new tax filing season gets underway, taxpayers have more than just one deadline to remember. From advance tax payments and Income Tax Return (ITR) filing to tax audits, belated returns and revised returns, the compliance calendar for Assessment Year (AY) 2026-27 spans several months.

Tax experts say keeping track of these milestones can help taxpayers avoid interest, penalties and unnecessary compliance issues later.

Advance Tax Installments Come First

For taxpayers liable to pay advance tax, compliance begins well before the ITR filing season.

The four advance tax instalment dates during the financial year are:

June 15
September 15
December 15
March 15

Missing these installments may attract interest under Sections 424 and 425 of the Income Tax Act, 2025, which correspond to Sections 234B and 234C of the Income Tax Act, 1961.

Interest under Section 424 may apply if the advance tax paid is less than 90 per cent of the assessed tax. In such cases, interest is levied at 1 per cent per month, or part thereof, on the shortfall.

Taxpayers who delay or underpay individual advance tax installments may also be liable to pay interest under Section 425 at the same rate for the period of default.

July 31: The Biggest Deadline for Individual Taxpayers

For salaried employees, pensioners and most taxpayers not covered under audit provisions, July 31, 2026 remains the principal ITR filing deadline.

Submitting the return within the due date helps taxpayers avoid late filing fees, interest on unpaid tax and, in certain cases, protects their ability to carry forward eligible losses.

Experts advise taxpayers not to wait until the final day to begin the filing process. Instead, they recommend verifying documents and tax details well in advance to minimise last-minute errors or technical issues.

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Some Business Taxpayers Have Until August 31

Not every taxpayer follows the same filing calendar.

Certain individuals with business or professional income who file ITR-3 or ITR-4 may have a filing deadline of August 31, depending on their income profile and audit requirements.

Taxpayers should carefully determine the due date applicable to their category instead of assuming that the July 31 deadline applies universally.

September and October Are Crucial for Audit Cases

For taxpayers whose accounts are subject to tax audit, two important compliance milestones fall later in the year.

Generally, the tax audit report must be submitted by September 30, while the corresponding income tax return should be filed by October 31.

It is recommended to complete reconciliations of books of accounts along with Form 26AS, the Annual Information Statement (AIS), the Taxpayer Information Summary (TIS) and audit report details before filing the return.

Thorough reconciliation reduces the likelihood of discrepancies that could trigger tax notices later.

December 31: Final Opportunity to File a Belated Return

Taxpayers who miss their original filing deadline are not immediately out of options.

December 31, 2026 is the last date to submit a belated return for AY 2026-27.

However, experts caution that filing after the original due date could still result in late fees, interest and other restrictions under the Income Tax Act.

Taxpayers are advised to file within the prescribed deadline wherever possible.

March 31, 2027: Extended Window for Revised Returns

One of the notable changes under the Income Tax Act, 2025 relates to revised returns.

From AY 2026-27 onwards, taxpayers who discover omissions or errors after filing their returns can submit a revised return until March 31, 2027, which marks the end of the relevant assessment year.

The extended timeline provides taxpayers with greater flexibility to correct mistakes. Ensuring accuracy while filing the original return remains the best approach.

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Why Planning Ahead Matters

Tax compliance now extends far beyond filing an annual return.

With advance tax payments, audit requirements, belated returns and revised return provisions spread across the financial year, taxpayers need to monitor multiple deadlines to remain compliant.