Interest under sections 234A, 234B and 234C, worked out month by month
When you file your income-tax return, the utility adds three kinds of interest: 234A for filing after the due date, 234B when advance tax paid by 31 March was less than 90% of the tax, and 234C when instalments were paid late or short. This 234A 234B 234C interest calculator works out all three from your actual dates and payments, shows each month and each instalment, and tells you how much tax and interest is still to pay.
It covers FY 2025-26 (AY 2026-27), the last year under the Income-tax Act, 1961, and tax year 2026-27, where the Income-tax Act, 2025 carries the same rules as sections 423, 424 and 425. Planning ahead for this year instead? The advance tax calculator uses the same engine. It is an informational estimate, not tax advice.
How to use the 234A, 234B & 234C Interest Calculator
- Choose the year and return type; the due date fills in (edit it if your case differs).
- Enter the tax on total income (with surcharge and cess) and your TDS, TCS and reliefs from Form 26AS or the AIS.
- Type the advance tax paid in each window, and tick presumptive income or the senior-citizen exemption if they apply.
- Add self-assessment tax payments with dates and the date you file. Pay what is left on the filing date fills the exact amount.
- Read the three interest figures and the tables; Copy summary keeps them for your records.
234A, 234B & 234C Interest Calculator features
All three sections together
Late return, advance tax under 90% and instalment shortfalls, each with its own table.
Month or part of a month
Every part month counts as a whole month and amounts are rounded down to ₹100, as Rule 119A requires.
Payments applied the legal way
Self-assessment tax goes to interest first, then tax, and 234B runs on the reduced amount from the next month.
Exclusions in 234C
Tax on capital gains, dividends, lottery winnings or first-year business income is left out of instalments due before it arose.
Old and new section numbers
234A, 234B and 234C are shown next to sections 423, 424 and 425 of the 2025 Act, looked up from the CBDT’s official table.
Due dates used for the return
The 31 August date for non-audit business and professional returns was added by the Finance Act, 2026. Interest under 234A is charged only when the return is filed after the due date; the separate late-filing fee is not part of this calculation.
| Return type | FY 2025-26 (AY 2026-27) | Tax year 2026-27 |
|---|---|---|
| No business income (ITR-1, ITR-2) | 31 July 2026 | 31 July 2027 |
| Business or profession, no audit (ITR-3, ITR-4) | 31 August 2026 | 31 August 2027 |
| Audit cases and companies | 21 November 2026 (extended from 31 October) | 31 October 2027 |
| Transfer-pricing report cases | 30 November 2026 | 30 November 2027 |
Worked example: a freelancer who paid only part of the advance tax
Tax of ₹2,21,000 less TDS of ₹1,00,000 leaves ₹1,21,000. She paid ₹30,000 in August and ₹40,000 in March. 234C: June ₹18,100 × 3% = ₹543, September ₹24,400 × 3% = ₹732, December ₹60,700 × 3% = ₹1,821 and March ₹51,000 × 1% = ₹510 — ₹3,606. 234B: ₹70,000 is under 90% of ₹1,21,000, so 1% a month on ₹51,000 for April to September (6 months) = ₹3,060. 234A: due 31 August, filed 20 September — one month on ₹51,000 = ₹510.
Interest totals ₹7,176, so she pays ₹58,176 as self-assessment tax. Had she paid only ₹51,000, the law would treat ₹7,176 of it as interest, leaving tax unpaid and interest still running.
Limits of this estimate
- 234B is counted to the filing date; the department counts to the date it processes the return, so a balance left unpaid keeps adding 1% a month.
- Interest after a reassessment or an order that changes the income, updated returns, non-residents and companies’ special rules are not modelled.
- Plan the next year’s instalments with the tax and GST compliance calendar and check TDS with the TDS calculator.
234A, 234B & 234C Interest Calculator FAQ
How is interest under 234A calculated?
1% for every month or part of a month from the day after the due date to the date you file, on the tax still unpaid on the due date — after advance tax, TDS, TCS, reliefs and self-assessment tax paid on or before the due date.
How do I use a 234B calculator for income tax?
Enter the tax, TDS and advance tax paid by 31 March. If advance tax is under 90% of the tax after TDS, 234B charges 1% a month from 1 April on the shortfall until it is paid; this calculator shows each period.
How does the 234C calculator count instalments?
Shortfalls against 15%, 45%, 75% and 100% of the tax by 15 June, 15 September, 15 December and 15 March, at 1% a month for three months (one month in March). Paying 12% by June and 36% by September avoids interest for those two dates.
Is interest charged if I pay the tax before the due date but file late?
Not under 234A on that tax, following the Supreme Court in CIT v. Pranoy Roy. 234B and 234C still apply if advance tax was short.
What are the new section numbers for 234A, 234B and 234C?
Under the Income-tax Act, 2025 they are sections 423, 424 and 425, from tax year 2026-27. FY 2025-26 returns still use the 1961 Act numbers.
Is this tax advice?
No. It is an informational estimate; the department’s processing decides the final interest. Check large amounts with a tax professional.