Interest on ₹10,000 of unpaid tax for a late return

If the return is filed after the due date and ₹10,000 of tax is still unpaid, section 423 of the Income-tax Act, 2025 charges simple interest of 1% a month on that amount: ₹100 a month.

By months of delay

Months	Interest	Tax plus interest
1	₹100	₹10,100
2	₹200	₹10,200
3	₹300	₹10,300
4	₹400	₹10,400
5	₹500	₹10,500
6	₹600	₹10,600
8	₹800	₹10,800
10	₹1,000	₹11,000
12	₹1,200	₹11,200
18	₹1,800	₹11,800
24	₹2,400	₹12,400

What this tells you

The interest grows in a straight line, because it is simple, not compound: twice as long means twice as much.
Paying the tax before filing stops the interest on the amount paid, because the tax on which interest is charged is reduced by tax paid.
This is only the interest. A fee under section 428 (up to ₹1,000 if the total income is not more than ₹5,00,000, otherwise ₹5,000) is charged separately for filing late.
Counting months: this table counts whole months. See the calculator for dates and how a part of a month is shown.

Common questions

How much interest on ₹10,000 of tax filed late?

₹100 a month, so ₹300 for 3 months and ₹600 for 6 months (1% a month, section 423).

Calculate with your dates

Sources

The Income-tax Act, 2025 (Act No. 30 of 2025), as published in the Gazette of India, Extraordinary (egazette.gov.in), read from the PDF on 13 November 2026. Sections used: 263(1)(c) (due dates), 398(3)(a) (late TDS and TCS interest), 423 (late return interest), 424 (advance tax default), 425 (advance tax deferment), 426 (excess refund), 427 (late statement fee), 428 (late return fee).
Commencement and the repeal of the 1961 Act: section 1(3) (in force on 1 April 2026) and section 536 of the same Act, and the CBDT's "FAQs on Interplay and Transition to the Income-tax Act, 2025" (incometaxindia.gov.in), questions 1.12, 3.5 and 6.1, read on 13 November 2026.
Counting months: sections 398(3)(a) and 424 say "every month or part of a month", and the CBDT's FAQs (Q on interest for defaults in deducting or depositing TDS and for advance tax, read 13 November 2026) say "per month or part thereof". The Act itself leaves "the rounding off of periods when a fraction of a month is involved" to the rules it empowers the Government to make (the list of rule-making powers, clause (u)); those Income-tax Rules were not read. This site therefore counts every started month, measured from the starting date (28 June to 2 July is one month; 10 January to 12 February is two), which matches "month or part thereof" but the rules may fix the starting-date convention differently. Section 423 itself says only "number of months comprised in the period", so its calculator also shows the whole-month count.

Rates and fees read on 13 November 2026 from the Income-tax Act, 2025 as published in the Gazette. Rules can be amended, and the portal or your assessing officer computes the final amount. This site does the arithmetic and is not tax advice; it is not connected with the Income Tax Department.