The due date for filing your return for FY 2025-26 (assessment year 2026-27) was 31 July 2026. If you missed it, you can still file a belated return under Section 139(4) up to 31 December 2026. You should do it now rather than in December, and the reason is not just the fee.
There are three costs. Two are obvious and small. The third is the one nobody warns you about, and it can be far larger than the other two combined.
Cost 1: the late filing fee (Section 234F)
| Your total income | Fee |
|---|---|
| Up to ₹5 lakh | ₹1,000 |
| Above ₹5 lakh | ₹5,000 |
Flat, one-time, and payable whether or not you owe any tax. Filing on 1 August and filing on 30 December cost the same fee.
Cost 2: interest on unpaid tax (Section 234A)
1% per month, or part of a month, on any tax still outstanding, running from the day after the due date until you file. Note the phrase part of a month — there is no pro-rating. Filing on 1 September rather than 31 August costs a full extra month of interest.
If your tax was fully covered by TDS and you owe nothing, this is zero. If you owe, it compounds your delay directly. Work out what you actually owe with the Income Tax Calculator, and if you have non-salary income, check whether advance tax was due with the Advance Tax Calculator — Sections 234B and 234C add separate interest for shortfalls there.
Cost 3: you lose the old regime — permanently, for that year
This is the expensive one, and it surprises people.
The new regime has been the default since AY 2024-25. Choosing the old regime is an opt-out, and the opt-out is only valid if it is exercised on or before the Section 139(1) due date:
- Salary and other non-business income (ITR-1, ITR-2): you choose in the return itself — but the return has to be on time.
- Business or professional income (ITR-3, ITR-4): you must file Form 10-IEA on or before the due date.
Either way, a belated return can only be filed under the new regime. Filing Form 10-IEA late does not help. Filing a revised return afterwards does not restore the choice. Switching to ITR-3 does not create a loophole — the timeliness condition sits in Section 115BAC itself, not in the form you pick.
But here is the honest part: for most people this costs nothing
The new regime got considerably more generous. A ₹75,000 standard deduction, and a Section 87A rebate that takes tax to zero on taxable income up to ₹12 lakh. For a large majority of salaried filers it now wins outright, so being locked into it is not a loss at all.
Take someone on ₹18 lakh with a fairly typical deduction set — ₹2.4 lakh HRA, ₹1.5 lakh under 80C, ₹25,000 under 80D, ₹2 lakh of home loan interest:
| Regime | Approximate tax |
|---|---|
| Old regime, with all those deductions | ₹1,59,000 |
| New regime, standard deduction only | ₹1,51,000 |
The new regime is cheaper. This person lost nothing by filing late except the fee.
Who does get hurt
The lock-out bites when your deductions are genuinely large. Same ₹18 lakh salary, but a metro renter with ₹4 lakh of HRA exemption, ₹1.5 lakh 80C, ₹50,000 80D and ₹2 lakh home loan interest — roughly ₹8 lakh of deductions in total:
| Regime | Approximate tax |
|---|---|
| Old regime | ₹1,07,000 |
| New regime (forced) | ₹1,51,000 |
That is roughly ₹44,000 — about nine times the ₹5,000 fee. As a rough rule of thumb, at this income level you need somewhere north of ₹7-8 lakh of total deductions before the old regime pulls ahead, and that generally means high metro rent plus a home loan plus a full 80C.
Run your own numbers both ways with the Old vs New Tax Regime Comparator before assuming either way. The crossover shifts with your income and your specific deductions.
One more consequence: carried-forward losses
File late and you lose the right to carry forward business losses and capital losses to future years. If you had a bad year in equities or your business made a loss, that is a real cost that shows up years later when you cannot set it off against a gain. Loss from house property is the exception — that carry-forward survives a belated return.
What to actually do
- File this week, not in December. The 234F fee is fixed, but 234A interest is per month or part of a month. Every calendar month you wait adds 1% of your outstanding tax for no benefit whatsoever.
- Recompute under the new regime before you file. If you had been planning around old-regime deductions, your actual liability is different from what you expected.
- Pay the self-assessment tax first, then file. Interest runs until the tax is paid, not until the return is submitted.
- For next year, file Form 10-IEA on time if you have business income and want the old regime. It takes a few minutes and it is the whole ball game.
And if you are past 31 December, the belated window closes too. After that the only route is an updated return under Section 139(8A), which carries additional tax on top — a considerably worse position than a ₹5,000 fee.
Related calculators
- Old vs New Tax Regime Comparator — see which regime actually costs you less
- Income Tax Calculator — work out what you owe
- Advance Tax Calculator — check for 234B/234C interest on non-salary income
Applies to FY 2025-26 (AY 2026-27): due date 31 July 2026 for non-audit cases, belated return window to 31 December 2026. Tax figures are illustrative and rounded; your own numbers will differ. General information, not personalised tax advice — for a large loss carry-forward or a complex case, speak to a chartered accountant.
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