Under the Income-tax Act, 1961, the income of a "previous year" was charged to tax in the following…

The 2025 Act replaces the pair of previous year and assessment year with one concept, the "tax year", defined in section 3. Section 4(2) charges income-tax "on the total income of the tax year of every person", so the year of earning and the year of charge are the same. Section 536(3) reads references to a tax year beginning on or before 1 April 2025 as references to the corresponding previous year under the repealed Act. Nothing in the Act moves to a calendar year.