I spotted a mistake after filing, how long to revise?

Short answer: if you have already filed your return and then find that you left something out or stated something wrongly, you can file a revised return. For a return for assessment year (AY) 2026-27 (income of FY 2025-26), the Income-tax Act, 1961 allows a revised return "at any time before the end of the relevant assessment year or before the completion of the assessment, whichever is earlier" (s.139(5), Income-tax Act, 1961, as substituted by Act 4 of 2026). AY 2026-27 ends on 31 March 2027. The earlier cut-off, three months before the end of the year, has gone. A new fee provision, s.234-I, now sits beside this rule, so read that part before you file.

The situation

You filed. Then the Form 26AS or AIS refreshes, a bank certificate arrives late, or you realise a deduction was left out, an interest income was missed, or the wrong bank account was entered. The return is on the portal, verified, and the question is simple: is it too late to fix?

Usually it is not. The law gives a specific route for exactly this, and it is not the same thing as a belated return or an updated return. Knowing which one fits saves you from using the wrong form.

What the law says now

The text of s.139(5), Income-tax Act, 1961, as it stands after Act 4 of 2026, reads: "If any person, having furnished a return under sub-section (1) or sub-section (4), discovers any omission or any wrong statement therein, he may, subject to the provisions of section 234-I, furnish a revised return at any time before the end of the relevant assessment year or before the completion of the assessment, whichever is earlier."

Three things to take from it.

1. It works only if you filed a return first. The revised return is available to a person who furnished a return under s.139(1) (on time) or s.139(4) (belated). If you never filed at all, this is not your section.

2. The reason must be an omission or a wrong statement. You "discover" something left out or wrongly stated. It is for genuine corrections, not for starting afresh with a different story.

3. The clock is the end of the assessment year, or completion of the assessment, whichever comes first. If the department finishes the assessment before 31 March 2027, the window closes at that point.

The Finance Act, 2026 (Act 4 of 2026) made this change in the 1961 Act with effect from 1 March 2026 (s.5(b), Finance Act, 2026). Before it, the same sub-section read "at any time before three months prior to the end of the relevant assessment year or before the completion of the assessment, whichever is earlier". So the window is now three months longer than in older guidance. Articles and checklists written before 2026 that say "31 December" for a revised return are out of date for this purpose.

The section 234-I fee

The same Act inserted a new s.234-I in the 1961 Act, with effect from 1 March 2026 (s.16, Finance Act, 2026). It reads: "Without prejudice to the provisions of this Act, where any person furnishes a return of income under sub-section (5) of section 139, beyond nine months but before twelve months from the end of the relevant assessment year, he shall pay by way of a fee,— (a) a sum of one thousand rupees, if the total income of such person does not exceed five lakh rupees; (b) a sum of five thousand rupees, in any other case."

Two honest points here.

First, the fee is tied to a window counted from the end of the assessment year: "beyond nine months but before twelve months from the end of the relevant assessment year". Section 139(5) of the 1961 Act, in the same Act's words, lets a revised return be furnished only "before the end of the relevant assessment year". The two sets of words do not fit together neatly for an AY 2026-27 return, and we have not found any text that explains how they are meant to be read. So we do not say that the fee applies, or that it does not apply, to a revised return filed before 31 March 2027. Ask a CA to confirm the position before you file.

Second, the practical answer is the same either way: do not wait. File the revised return as soon as you know the figures. Early filing keeps you well inside the s.139(5) window. If the portal shows a fee for your case, check it with your CA and keep the receipt.

The fee amounts, where they apply, depend on total income: one thousand rupees if total income does not exceed five lakh rupees, five thousand rupees in any other case (s.234-I, Income-tax Act, 1961).

The Income-tax Act, 2025 timing for later years

The Income-tax Act, 2025 applies from tax year 2026-27 (income of FY 2026-27, filed in 2027). Its revised-return rule is different. As amended by the Finance Act, 2026, s.263(5), Income-tax Act, 2025 says a person who has filed under s.263(1) or (4) and discovers an omission or wrong statement "may, subject to the provisions of section 428(b), furnish a revised return at any time within twelve months from the end of the relevant tax year, or before the completion of the assessment, whichever is earlier" (s.66(b), Finance Act, 2026).

The matching fee is s.428(b), Income-tax Act, 2025: where a person "furnishes a return of income under section 263(5) beyond nine months from the end of relevant tax year", the fee is ₹1,000 if total income does not exceed ₹5 lakh and ₹5,000 in any other case. Here the window and the fee line up: revised return within nine months of the end of the tax year carries no such fee, and from nine to twelve months it does.

The official mapping table links s.139 of the 1961 Act to s.263 of the 2025 Act. For your AY 2026-27 return, though, the 1961 Act rule above is the one that governs.

Which route fits your mistake

A belated return under s.139(4) can be furnished "at any time before three months prior to the end of the relevant assessment year or before the completion of the assessment, whichever is earlier" (s.139(4), Income-tax Act, 1961). That is why 31 December of the assessment year is the usual cut-off for a belated return, while a revised return can now run to the end of the year.

An updated return under s.139(8A) can be furnished "at any time within forty-eight months from the end of the relevant assessment year", but it does not apply if it is a return of loss, if it reduces the total tax liability, or if it increases the refund due (s.139(8A) and its first proviso, Income-tax Act, 1961). So it is a route to add income and pay more, not a way to claim more refund.

Step by step

• Write down exactly what was wrong. Which schedule, which figure, which direction. A one-line description helps the reviewer and you.
• Collect the paper. Interest certificates, Form 16, capital gains statements, rent receipts, challans. Take figures from the documents, not memory.
• Recompute the tax. If more tax is due, pay it before you submit the revised return, and enter the challan details. Interest may be payable on the shortfall, so ask your CA to compute it.
• Use the revised return option on the e-filing portal for the same AY. Check the portal for the exact screen and the details it asks for, such as the original acknowledgement number.
• Prepare the whole return. Treat the revised return as a complete return, not a note of the corrected item, and complete every schedule.
• Check the form. If the ITR form you used no longer fits your facts after correction, check the portal and your CA on which form applies.
• Submit and verify. Check the portal for how and by when the return must be verified.
• Keep both acknowledgements. The first and the revised.

What not to do

• Do not wait for a notice. Once the assessment is complete, the revised-return window shuts, even before the year ends.
• Do not try to file a second original return. Use the revised return route (check the portal for how).
• Do not claim a refund you cannot support. Keep the documents for every figure.
• Do not use a revised return to add a new business or change the nature of the case without checking the form and rules first.
• Do not rely on pre-2026 articles for the cut-off date.

What to do now

• Next step: list the exact error, recompute the tax and, if tax is short, pay it and then file the revised return for the same AY (s.139(5), Income-tax Act, 1961).
• Deadline: the end of the relevant assessment year, 31 March 2027 for AY 2026-27, or completion of the assessment if that comes earlier (s.139(5), Income-tax Act, 1961, as substituted by Act 4 of 2026).
• Consequence of missing it: a revised return is no longer available; if income was under-reported the route left is an updated return, which cannot reduce tax or increase a refund (s.139(8A), Income-tax Act, 1961). Section 234-I, Income-tax Act, 1961, also carries a fee for a return under s.139(5) filed in the window it names; ask a CA how it applies to you.

Have a CA review your facts before you act or file.

FAQs

Is there a limit on how many times I can revise?
The text of s.139(5) does not set a number. Each revision must meet the same condition: you have discovered an omission or wrong statement, and you are inside the time limit.

Does the revised return replace the original?
Section 139(5) does not say so in words. Treat the revised return as a complete return in its own right, and ask a CA how it sits with the original.

My original return was a belated one. Can I revise it?
Yes. Section 139(5) covers returns furnished under s.139(1) or s.139(4).

I missed the revised return window. Is anything left?
If you under-reported income, an updated return under s.139(8A) is possible within forty-eight months from the end of the assessment year, subject to its other conditions. It cannot be used to reduce tax or increase a refund.

Is the 31 December date for revised returns still right?
Not for AY 2026-27 under the 1961 Act. That date came from the older text, which stopped three months before the end of the assessment year. The sub-section now runs to the end of the year.

What if I am revising a return for tax year 2026-27 onward?
The Income-tax Act, 2025 applies, and s.263(5) gives twelve months from the end of the tax year, with the s.428(b) fee for filings beyond nine months.

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