Interest & Penalty Calculator — Section 234A/B/C
Calculate interest for late filing (234A at 1%/month), advance tax default (234B at 1%/month), and instalment deferment (234C at 1%/month per quarter). Includes Section 234F late fee (&rupee;5,000 or &rupee;1,000). Updated for FY 2025-26 (AY 2026-27) with Finance Act 2025 rates.
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How to Use This Calculator
234A Late Filing tab
Enter your total tax liability, TDS paid, advance tax paid, the due date of filing (31 July for non-audit, 31 October for audit), and the actual filing date. Select whether your income is above or below &rupee;5 lakh (determines the 234F late fee). The calculator computes months of delay, 234A interest at 1% per month on unpaid tax, and the 234F late fee.
234B Advance Tax Default tab
Enter your total tax liability, TDS/TCS paid, advance tax paid, and the date of payment or assessment. The calculator checks if your advance tax is below 90% of assessed tax (after TDS). If yes, it computes 234B interest at 1% per month from 1 April of the assessment year to the payment date.
234C Instalment Default tab
Enter your total tax liability, TDS paid, and the advance tax paid in each quarter (Q1 through Q4). Choose whether you are under the presumptive scheme (44AD/44ADA). The calculator computes the shortfall at each due date (15 Jun, 15 Sep, 15 Dec, 15 Mar) and interest at 1% per month × 3 months for Q1-Q3, and 1 month for Q4.
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The Formula
Interest under Sections 234A, 234B, and 234C of the Income Tax Act, 1961:
Interest = Unpaid Tax × 1% × Number of Months
Unpaid Tax = Total Tax Liability − TDS − Advance Tax
Period: Due date of filing → Actual filing date
Part of a month = full month
Section 234F — Late Filing Fee:
Fee = &rupee;5,000 (or &rupee;1,000 if total income ≤ &rupee;5 lakh)
Section 234B — Advance Tax Default:
Trigger: Advance tax paid < 90% of assessed tax (after TDS)
Interest = Shortfall × 1% × Number of Months
Shortfall = Assessed Tax − Advance Tax Paid
Period: 1 April of AY → Date of assessment / payment
Section 234C — Instalment Default:
Q1 (15 Jun): Shortfall = 15% of tax − paid by Q1 → 1% × 3 months
Q2 (15 Sep): Shortfall = 45% of tax − cumulative paid → 1% × 3 months
Q3 (15 Dec): Shortfall = 75% of tax − cumulative paid → 1% × 3 months
Q4 (15 Mar): Shortfall = 100% of tax − cumulative paid → 1% × 1 month
Presumptive (44AD): 100% by 15 Mar → 1% × 1 month on shortfall
All interest rates are 1% per month (simple), not per annum. The “part of month = full month” rule means even a 1-day delay into the next month counts as a full additional month of interest.
Example
Rahul — Salaried professional who filed ITR late and underpaid advance tax
Rahul has a total tax liability of &rupee;5,00,000 for FY 2025-26. His employer deducted &rupee;3,80,000 as TDS. He paid no advance tax. He filed his ITR on 15 December 2026 instead of the 31 July due date.
Step 1: Section 234A Interest
Step 2: Section 234F Late Fee
Total penalty
Rahul’s total penalty of &rupee;11,000 on an unpaid tax of &rupee;1,20,000 shows why timely filing matters. Had he filed by 31 July and paid the remaining &rupee;1,20,000, his penalty would have been &rupee;0.