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Knowledge Bank / Income-tax Act, 2025 / Chapter XV - Return of Income

Section 266

Section 266: self-assessment

Section 266 requires taxpayers to settle up before they file: if tax is still payable after accounting for TDS, advance tax and other credits, the assessee must pay that tax - along with any interest and fee for delay - before furnishing the return under Section 263, 268, 280 or 294, and attach proof of payment.

Obligation to pay tax before filing

Where tax is payable on the basis of a return required under Section 263, 268, 280 or 294 (after accounting for the credits listed below), the assessee must pay that tax together with any interest and fee payable for delay in filing the return or for default/delay in advance tax payment, before furnishing the return. The return must be accompanied by proof of payment of the tax, interest and fee.

Credits accounted for before computing what's payable

Before working out the self-assessment tax due, the following amounts already available to the assessee are taken into account:

  • Tax already paid under any provision of the Act
  • Tax deducted or collected at source
  • Relief of tax claimed under Section 157
  • Relief of tax or deduction of tax claimed under Section 159(1) or 160 for tax paid in a country outside India
  • Relief of tax claimed under Section 159(2) for tax paid in a specified territory outside India
  • Tax credit claimed to be set off as per Section 206(2)(e) to (h) and 206(3) and (4)
  • Any tax or interest payable according to Section 391(2)

Order of adjustment for a shortfall

If the amount paid by the assessee falls short of the aggregate tax, interest and fee payable, the amount paid is first adjusted toward the fee payable, then toward the interest payable, and the balance (if any) toward the tax payable.

How interest is computed

Interest payable under Section 423 (for delay in furnishing the return) is computed on the tax on total income declared in the return, reduced by advance tax paid, TDS/TCS, and the various reliefs/tax credits listed above.

Interest payable under Section 424 is computed on the "assessed tax" - or on the shortfall between advance tax paid and the assessed tax. "Assessed tax" here means tax on the total income declared in the return, reduced by TDS/TCS under Chapter XIX-B, the Section 157/159/160 reliefs, and the Section 206 tax credit.

Effect on regular assessment and default

After a regular assessment under Section 270 or 271, or an assessment under Section 294, any amount paid under this section is deemed to have been paid toward that assessment.

If an assessee fails to pay the whole or part of the tax, interest or fee due under this section, they are deemed to be an assessee in default for the unpaid amount, and all provisions of the Act apply accordingly - without prejudice to any other consequences the assessee may face.

Frequently asked questions

Do I need to pay tax before I file my return?

Yes - Section 266 requires that if tax is still payable after accounting for TDS/TCS, advance tax and other reliefs already claimed, you must pay it (with applicable interest and fee) before furnishing the return, and attach proof of payment.

What happens if I underpay my self-assessment tax?

If you fail to pay the whole or part of the tax, interest or fee due under Section 266, you are deemed to be an "assessee in default" for the unpaid amount, and the Act's default-recovery provisions apply.

If I pay only part of what's due, what gets paid off first?

The shortfall is adjusted first toward the fee payable, then toward interest, and only the balance is treated as tax paid.

Related sections

  • Section 263 - filing of return of income
  • Section 267 - tax on updated return

Want this applied to your actual filing, not just explained?

Get help computing and paying your self-assessment tax

Last updated 9 September 2026

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