Self-assessment tax

Self-Assessment Tax: Step-by-Step Computation, Challan 280 Guide, and Section 234B/234C Interest for AY 2026-27

Self-assessment tax is the final balance of income tax you must clear before filing your ITR. Under Section 140A of the Income-tax Act, 1961, you subtract TDS, TCS, and advance tax from your total liability, add Section 234B and 234C interest, and pay via Challan ITNS 280 before submitting the return. For AY 2026-27 (FY 2025-26), the due date is 31 July 2026 — and the Section 234B interest clock has been running since 1 April 2026.

What Is Self-Assessment Tax and Why Section 140A Is Non-Negotiable

Section 140A does not offer a grace window — it imposes a mandatory pre-filing obligation. The provision requires every taxpayer to:

1. Compute total income and apply the applicable tax rates for the year.
2. Reduce TDS, TCS, advance tax installments, and any MAT/AMT credit.
3. Calculate interest under Sections 234A, 234B, and 234C as applicable.
4. Pay the aggregate balance before the return is submitted.

The phrase "before" matters because the ITR validation engine on the Income Tax e-Filing portal cross-checks your declared payments against OLTAS (Online Tax Accounting System) records in real time. If your challan is not yet reflecting in OLTAS at the moment you file, the return either rejects or generates an immediate demand on processing under Section 143(1).

Unlike employer TDS — where the deductor takes responsibility — self-assessment tax is entirely the taxpayer's initiative. No one reminds you, no automatic deduction triggers, and no extension of time is granted just because you were unaware of the shortfall.

Who Must Pay Self-Assessment Tax?

Any taxpayer whose net tax liability after all pre-paid taxes remains positive — even by ₹1 — is required to pay. There is no de-minimis exemption. Common profiles where a balance routinely arises:

• Salaried employees with outside income: Freelance, rental, interest, or capital gains not declared to the employer for TDS adjustment produce a gap between Form 16 and the full-year liability.
• Consultants and professionals: Advance tax estimates based on early-year income often fall short when Q3 or Q4 billings surge.
• Equity and MF investors with March gains: Anyone who redeemed listed equity funds or shares between January and March 2026 missed the 15 December advance-tax deadline and now carries the entire capital gains tax as self-assessment.
• NRIs with India-source income: Flat-rate TDS on rental or interest income may not match the slab computation, especially after applying treaty benefits.
• Presumptive taxpayers under Sections 44AD/44ADA: The entire advance tax is due in one shot by 15 March. Underestimating March income leaves a self-assessment tail.

How to Compute Self-Assessment Tax: An Eight-Step Process

Step 1 — Compile Gross Total Income

Aggregate all five heads: salary (apply standard deduction of ₹75,000 under the new regime for salaried employees), house property, profits and gains of business or profession, capital gains, and other sources (bank interest, dividends, casual income). Download your AIS (Annual Information Statement) and TIS (Taxpayer Information Summary) from the e-Filing portal first and reconcile every line item before computing — the system will flag discrepancies during processing.

Step 2 — Apply Deductions (Old Regime Only)

If you filed Form 10-IEA to opt into the old tax regime, subtract Chapter VI-A deductions: Sections 80C, 80D, 80G, 80TTA, and so on. Under the new tax regime (the default), these deductions are unavailable — with the narrow exception of employer contributions to NPS under Section 80CCD(2), which remains deductible even in the new regime.

Step 3 — Arrive at Total Income

Total income = Gross total income minus allowable deductions. For special-rate income (equity LTCG under Section 112A, STCG under Section 111A, debt MF gains taxed at slab), segregate these before applying general slab rates.

Step 4 — Apply Slab Rates

New tax regime — default for AY 2026-27 (FY 2025-26), per Finance Act 2025:

Section 87A rebate (new regime, AY 2026-27): Up to ₹60,000 for total income not exceeding ₹12,00,000. This makes the effective tax nil for most taxpayers in this bracket — but the rebate does not apply to special-rate incomes such as STCG under Section 111A or LTCG under Section 112A. If your total income is ₹11 lakh but includes ₹2 lakh of STCG on listed shares, the STCG tax of ₹40,000 (at 20%) is still payable even though general slab tax is covered by the rebate.

Old regime slabs: Nil up to ₹2,50,000; 5% from ₹2.5L–₹5L; 20% from ₹5L–₹10L; 30% above ₹10L. Section 87A rebate capped at ₹12,500 for income up to ₹5 lakh.

Step 5 — Add Surcharge if Applicable

Surcharge applies when total income exceeds ₹50 lakh. Under the new regime, surcharge is capped at 25% regardless of income. Under the old regime, it ranges from 10% (₹50L–₹1Cr) to 37% (above ₹5Cr). Apply marginal relief where the surcharge pushes total tax above the incremental income above the threshold.

Step 6 — Add Health and Education Cess

Add 4% cess on the sum of income tax and surcharge. This applies universally — there is no exception, no exemption based on income level.

Step 7 — Subtract All Pre-Paid Taxes

Reduce: TDS from salary (as per Form 16), TDS on professional income (Form 16A), bank TDS on interest, TCS on purchases, and advance tax installments paid on 15 June, 15 September, 15 December, and 15 March. Cross-reference every figure against Form 26AS and AIS — if a deductor failed to file their TDS return, the credit will not appear, and claiming it in the ITR will trigger a mismatch demand.

Step 8 — Add Interest and Arrive at Net Payable

Add Section 234B and 234C interest as applicable. The formula:

> Self-Assessment Tax = Income Tax + Surcharge + Cess + Interest (234A+234B+234C) − TDS − TCS − Advance Tax

Worked Example: AY 2026-27 Computation with Real Rs. Numbers

Profile: Aditya Seth, independent technology consultant, FY 2025-26

Income:

• Consultancy fees from three companies: ₹28,00,000 (clients deducted TDS @ 10% = ₹2,80,000)
• Bank FD interest: ₹40,000 (bank deducted TDS @ 10% = ₹4,000)
• Total income: ₹28,40,000
• Advance tax paid during the year: ₹0 (Aditya assumed employer/client TDS would be sufficient)

Tax under new regime (default):

No surcharge (income below ₹50 lakh). No 87A rebate (income above ₹12 lakh).

Credits: Total TDS = ₹2,80,000 + ₹4,000 = ₹2,84,000. Advance tax = ₹0.

Assessed tax for Section 234B = ₹4,49,280 − ₹2,84,000 = ₹1,65,280

90% threshold = ₹1,48,752. Advance tax installments = ₹0. Since ₹0 < ₹1,48,752, Section 234B is triggered.

Scenario A — Pays self-assessment tax on 25 May 2026:

• 234B period: 1 April to 25 May = 2 full months (any part of a month counts as a whole month)
• 234B interest: ₹1,65,280 × 1% × 2 = ₹3,306
• Total to pay on challan: ₹1,68,586

Scenario B — Defers payment to 30 July 2026 (files ITR at the last moment):

• 234B period: 1 April to 30 July = 4 full months
• 234B interest: ₹1,65,280 × 1% × 4 = ₹6,611
• Total to pay on challan: ₹1,71,891

By paying two months earlier, Aditya saves ₹3,305. Scale this up: a taxpayer with ₹5 lakh in self-assessment tax pays ₹10,000 extra per month they delay. There is no benefit to waiting until the filing deadline.

Interest Under Sections 234A, 234B, and 234C: What Triggers Each

Section 234B — Advance Tax Shortfall

Section 234B applies when the total advance tax paid (including TDS and TCS) is less than 90% of the assessed tax. For this section, "assessed tax" means total tax minus TDS and TCS — effectively the net amount you owe before advance installments.

• Rate: 1% simple interest per month, or part thereof.
• Period: From 1 April of the assessment year until the date of payment of self-assessment tax.
• Base: Assessed tax minus advance tax installments actually paid.

If your TDS alone exceeds 90% of your total liability — common for salaried employees with no outside income — Section 234B does not apply. Freelancers, business owners, and investors with significant capital gains almost always trigger it.

Section 234C — Quarterly Advance Tax Deferment

Section 234C charges interest for under-payment at each quarterly advance-tax milestone during the financial year itself. The benchmark percentages for non-corporate taxpayers:

Interest at 1% per month applies on any shortfall at Q1, Q2, and Q3 for 3 months each; at Q4 for 1 month. Section 234C and Section 234B both apply simultaneously — 234C covers deferment during the year, and 234B picks up from 1 April of the assessment year.

Critical exception: If you received an unexpected capital gain or a one-time receipt after the 15 December deadline, the Section 234C shortfall attributable to that income is waived. This relief is built into the proviso to Section 234C — document the unexpected nature of the receipt clearly.

Section 234A — Late Filing of Return

Section 234A levies 1% per month on tax remaining unpaid on the original due date if the ITR is filed late. The base is: tax payable minus all credits, including self-assessment tax paid before (but after) the due date.

Practical implication: If you pay the full self-assessment tax by 31 July 2026 but file the ITR in October 2026, your Section 234A base is ₹0 — no interest accrues. Pay on time, file late: bad. Pay late, file late: worse. Pay on time, file on time: ideal.

How to Pay Self-Assessment Tax via Challan ITNS 280: Step by Step

All self-assessment tax payments in India use Challan ITNS 280 (commonly called Challan 280). Payments are made through the e-Pay Tax facility on the Income Tax e-Filing portal at unknown node.

Step 1: Log in with your PAN credentials. Go to e-File → e-Pay Tax, or click "e-Pay Tax" on the portal's quick-links dashboard.

Step 2: Click "+ New Payment" and select "Income Tax" as the tax applicable.

Step 3: Select the Assessment Year. For FY 2025-26 income, select AY 2026-27. Confirm this twice — an AY error cannot be fixed online and requires a written challan correction request to your Assessing Officer (AO), which typically takes 4–8 weeks to resolve.

Step 4: Under "Type of Payment," select "(300) Self Assessment Tax." The code 300 is distinct from:

• (100) Advance Tax — for installments paid during the financial year
• (400) Tax on Regular Assessment — for demand payments after scrutiny

Selecting the wrong minor head creates a mismatch that, again, requires a correction request to the TIN Facilitation Centre.

Step 5: Enter the tax amount and interest amount in their respective fields. Do not club both into a single "tax" amount — fill the interest field separately.

Step 6: Choose your payment mode. Net banking and UPI (up to ₹1 lakh per transaction on most banks) are the fastest — payment is credited to OLTAS typically within one working day. RTGS/NEFT is suitable for large amounts. Debit card acceptance varies by bank. Physical payment at an authorised bank branch using a paper Challan 280 is still permitted but is slower.

Step 7: After successful payment, download the Challan ITNS 280 receipt immediately. Save and note:

• BSR Code — 7-digit code identifying the bank branch
• Challan Serial Number — 5-digit transaction sequence number
• Date of deposit
• Amount

Step 8: Wait for the payment to appear in Form 26AS (check via the e-Filing portal under Annual Tax Statement or on the TRACES portal). Payments typically reflect within 3–5 working days.

Step 9: When filling the ITR, go to Schedule IT — Details of Advance Tax and Self-Assessment Tax Payments. Enter the BSR code, serial number, date, and amount exactly as shown on the challan. A single incorrect digit causes the credit to go unmatched in processing.

AIS and Form 26AS Reconciliation Before You Compute

The Annual Information Statement (AIS) on the e-Filing portal now aggregates data from employers, banks, brokerages, mutual fund registrars, GST filings, property registrations, and foreign remittances. Before you compute self-assessment tax:

• Download your AIS from the portal's Services → Annual Information Statement section.
• Verify every TDS entry: if a client deducted TDS but has not filed their TDS return, the amount will not appear in your AIS or 26AS. You cannot claim a credit that is not visible — follow up with the deductor to file their correction return before you file your ITR.
• Watch for income entries you may have overlooked: dividend income auto-reported by companies, savings-account interest reported by banks, FD interest, MF redemptions. The 143(1) intimation will flag anything in AIS that you did not disclose.
• If you believe an AIS entry is wrong, submit feedback directly in the AIS (mark it "Incorrect" or "Amount is partially correct"). This updates the TIS, which feeds into your pre-filled ITR.

Reconciling AIS before computing tax prevents you from underestimating income — which means undercomputing liability — which means a demand notice with interest after filing.

Common Mistakes That Derail Your ITR Processing

1. Wrong assessment year on Challan 280. The most frequent and most damaging error. For FY 2025-26 income, you need AY 2026-27 — not AY 2025-26. Once paid, there is no digital correction; you must approach your AO with a letter, Form 26B (application for refund, if applicable), and supporting documents. This takes months and does not stop the interest clock.

2. Selecting "(100) Advance Tax" instead of "(300) Self Assessment Tax." The payment hits your account but under the wrong minor head. The ITR engine treats it as an advance tax credit, not a self-assessment credit, and may still raise a demand if the timing is after 31 March of the financial year. Correction requires a challan correction request to the TIN FC with a copy of the challan.

3. Omitting cess or surcharge from the computation. Tax at slab rates is not the final number. Cess at 4% adds to every rupee of tax — a ₹4,00,000 tax bill carries ₹16,000 in cess that many people forget. On top of that, surcharge can add 10–25% on the base tax for higher-income taxpayers.

4. Filing the ITR before the challan appears in Form 26AS. If you pay on a Friday evening and file Saturday morning, the bank may not have processed the transaction yet. The system will not credit your payment and will generate a demand. Always confirm the 26AS entry before filing.

5. Including only the tax amount on the challan, not the interest. Self-assessment tax should include interest under 234B, 234C, and (if filing late) 234A. If you pay only the principal and enter zero interest in the ITR, the processing system computes the interest itself and raises a separate demand for the shortfall. Pay tax and interest together on one challan, filling both fields correctly.

6. Ignoring TDS entries that are not in AIS. Claiming TDS that a deductor has not deposited or reported will trigger a 143(1) mismatch demand. Always verify that your claim matches what is visible in 26AS before filing.

7. Transposing digits in the BSR code or challan serial number. These fields are manually entered in most ITR forms. One wrong digit renders the credit untraceble. Cross-check digit-by-digit against the downloaded challan receipt before clicking submit.

Key Takeaways

• Section 140A mandates self-assessment tax for any taxpayer with a positive balance after TDS, TCS, and advance tax — there is no minimum threshold below which you are exempt.
• Compute using AIS-reconciled figures, not just Form 16 or client invoices. Missed income entries in the return trigger 143(1) demands with additional interest.
• The new tax regime is the default for AY 2026-27 (FY 2025-26). Apply the revised slabs per Finance Act 2025 — nil up to ₹4 lakh, stepping up to 30% above ₹24 lakh — and remember the 87A rebate does not shelter special-rate incomes like STCG and LTCG even if total income is within ₹12 lakh.
• Pay via Challan ITNS 280 on the e-Filing portal, selecting minor head (300) Self Assessment Tax and the correct assessment year. Save the BSR code, challan serial number, date, and amount — these go into Schedule IT of the ITR exactly as printed on the receipt.
• Section 234B interest at 1% per month has been accruing since 1 April 2026 for AY 2026-27 taxpayers who did not fully cover their liability through advance tax. Every month you delay payment adds to the cost — for a ₹2 lakh self-assessment balance, that is ₹2,000 per month of pure interest.
• Section 234C and 234B can both apply — 234C for quarterly shortfalls during the financial year, 234B for the post-March balance. They are not mutually exclusive and are computed on different bases and periods.
• Wait for the challan to reflect in Form 26AS (typically 3–5 working days) before filing the ITR. A premature filing creates a credit mismatch demand that then requires a manual rectification request under Section 154.