Think of Section 234B as the government's late fee for under-paying advance tax during the year. If you reach March 31st having paid less than 90% of your final tax liability, the Income Tax Department charges you interest starting April 1st — right from the first day of the assessment year — until they finish processing your return.
Who does this hit? Any assessee liable to pay advance tax under Section 208 (tax liability above ₹10,000 after TDS). The trigger is simple: if advance tax paid < 90% of assessed tax, Section 234B applies. Note the word assessed tax — this is not your gross tax. Assessed tax = Tax on total income − TDS/TCS deducted − relief for foreign taxes (Sections 90/90A/91) − MAT/AMT credit (Sections 115JAA/115JD). You always work with the net figure after these deductions.
The interest rate is 1% per month, computed as simple interest. Crucially, even a single day in a month counts as a full month — so 1 month 1 day = 2 months of interest. The interest runs from 1st April of the assessment year (the day after the financial year closes) to the date your return is processed under Section 143(1), or the date of regular assessment if a scrutiny assessment is made. There's a built-in relief: if you pay self-assessment tax under Section 140A before your return is processed, interest stops accumulating on the amount paid from that date. Any remaining shortfall keeps attracting interest until fully assessed. One more thing worth knowing for exams — if a reassessment under Section 147 increases your income, the interest under 234B gets recalculated on the enhanced amount from 1st April of the relevant AY to the date of reassessment order.
This section is exam gold — expect a 4–5 mark numerical that combines 234A, 234B, and 234C in one question. Master the assessed tax definition and the period calculation, and you'll rarely drop marks here.
Example 1: Basic Section 234B Calculation
Mr. Arjun Sharma's total income for FY 2024-25 results in a gross tax liability of ₹3,40,000. TDS deducted during the year = ₹80,000. Advance tax paid = ₹1,90,000. Return processed under Section 143(1) on 20th December 2025.
Step 1 — Compute Assessed Tax
Assessed Tax = Gross Tax − TDS
= ₹3,40,000 − ₹80,000
= ₹2,60,000
Step 2 — Check 90% Threshold
90% of ₹2,60,000 = ₹2,34,000
Advance tax paid = ₹1,90,000 < ₹2,34,000 → Section 234B applies
Step 3 — Shortfall Amount
₹2,60,000 − ₹1,90,000 = ₹70,000
Step 4 — Count Months
1st April 2025 → 20th December 2025
= 8 complete months + 20 days → 9 months (part month = full month)
Step 5 — Interest
₹70,000 × 1% × 9 = ₹6,300
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Example 2: Self-Assessment Tax Paid Mid-Way
Ms. Kavitha Iyer (FY 2024-25): Assessed tax = ₹1,60,000. Advance tax paid = ₹80,000. She pays ₹60,000 self-assessment tax on 31st August 2025. Return processed on 31st October 2025.
90% check: 90% × ₹1,60,000 = ₹1,44,000 > ₹80,000 → 234B triggered
Initial shortfall = ₹1,60,000 − ₹80,000 = ₹80,000
Period 1: 1 April 2025 → 31 August 2025 = 5 months
Interest = ₹80,000 × 1% × 5 = ₹4,000
Period 2: After ₹60,000 SAT paid:
Remaining shortfall = ₹1,60,000 − (₹80,000 + ₹60,000) = ₹20,000
1 September 2025 → 31 October 2025 = 2 months
Interest = ₹20,000 × 1% × 2 = ₹400
Total 234B Interest = ₹4,000 + ₹400 = ₹4,400
📖 Bare Act text — Section 234B, Income Tax Act 1961
(click to expand)
(1) Subject to the other provisions of this section, where, in any financial year, an assessee who is liable to pay advance tax under section 208 has failed to pay such tax or, where the advance tax paid by such assessee under the provisions of section 210 is less than ninety per cent. of the assessed tax, the assessee shall be liable to pay simple interest at the rate of one per cent. for every month or part of a month comprised in the period from the 1st day of April next following such financial year to the date of determination of total income under sub-section (1) of section 143 and where a regular assessment is made, to the date of such regular assessment, on an amount equal to the assessed tax or, as the case may be, on the amount by which the advance tax paid as aforesaid falls short of the assessed tax. Explanation 1.—In this section, "assessed tax" means the tax on the total income determined under sub-section (1) of section 143 and where a regular assessment is made, the tax on the total income determined under such regular assessment as reduced by the amount of,— (i) any tax deducted or collected at source in accordance with the provisions of Chapter XVII on any income which is subject to such deduction or collection and which is taken into account in computing such total income; (ii) any relief of tax allowed under section 90 on account of tax paid in a country outside India; (iii) any relief of tax allowed under section 90A on account of tax paid in a specified territory outside India referred to in that section; (iv) any deduction, from the Indian income-tax payable, allowed under section 91, on account of tax paid in a country outside India; and (v) any tax credit allowed to be set off in accordance with the provisions of section 115JAA or section 115JD. Explanation 2.—Where, in relation to an assessment year, an assessment is made for the first time under section 147 or section 153A, the assessment so made shall be regarded as a regular assessment for the purposes of this section. Explanation 3.—In Explanation 1 and in sub-section (3) "tax on the total income determined under sub-section (1) of section 143" shall not include the additional income-tax, if any, payable under section 143. (2) Where, before the date of determination of total income under sub-section (1) of section 143 or completion of a regular assessment, tax is paid by the assessee under section 140A or otherwise,— (i) interest shall be calculated in accordance with the foregoing provisions of this section up to the date on which the tax is so paid, and reduced by the interest, if any, paid under section 140A towards the interest chargeable under this section; (ii) thereafter, interest shall be calculated at the rate aforesaid on the amount by which the tax so paid together with the advance tax paid falls short of the assessed tax. (2A) (a) where an application under sub-section (1) of section 245C for any assessment year has been made, the assessee shall be liable to pay simple interest at the rate of one per cent. for every month or part of a month comprised in the period commencing on the 1st day of April of such assessment year and ending on the date of making such application, on the additional amount of income-tax referred to in that sub-section; (b) where as a result of an order of the Settlement Commission under sub-section (4) of section 245D for any assessment year, the amount of total income disclosed in the application under sub-section (1) of section 245C is increased, the assessee shall be liable to pay simple interest at the rate of one per cent. for every month or part of a month comprised in the period commencing on the 1st day of April of such assessment year and ending on the date of such order, on the amount by which the tax on the total income determined on the basis of such order exceeds the tax on the total income disclosed in the application filed under sub-section (1) of section 245C; (c) where, as a result of an order under sub-section (6B) of section 245D, the amount on which interest was payable under clause (b) has been increased or reduced, as the case may be, the interest shall be increased or reduced accordingly; (3) where, as a result of an order of reassessment or recomputation under section 147 or section 153A, the amount on which interest was payable in respect of shortfall in payment of advance tax for any financial year under sub-section (1) is increased, the assessee shall be liable to pay simple interest at the rate of one per cent. for every month or part of a month comprised in the period commencing on the 1st day of April next following such financial year and ending on the date of the reassessment or recomputation under section 147 or section 153A, on the amount by which the tax on the total income determined on the basis of the reassessment or recomputation exceeds the tax on the total income determined under sub-section (1) of section 143 or on the basis of the regular assessment as referred to in sub-section (1), as the case may be; (4) where, as a result of an order under section 154 or section 155 or section 250 or section 254 or section 260 or section 262 or section 263 or section 264, the amount on which interest was payable under sub-section (1) or sub-section (3) has been increased or reduced, as the case may be, the interest shall be increased or reduced accordingly, and— (i) in a case where the interest is increased, the Assessing Officer shall serve on the assessee a notice of demand in the prescribed form specifying the sum payable and such notice of demand shall be deemed to be a notice under section 156 and the provisions of this Act shall apply accordingly; (ii) in a case where the interest is reduced, the excess interest paid, if any, shall be refunded; (5) the provisions of this section shall apply in respect of assessments for the assessment year commencing on the 1st day of April, 1989 and subsequent assessment years.