Section 3 of Income Tax Act "Previous year defined"
For the purposes of this Act, "previous year" means the
financial year immediately preceding the assessment year :
Provided that, in the case of a business or profession newly set up, or a source of income newly coming into existence, in the said financial year, the previous year shall be the period beginning with the date of setting up of the business or profession or, as the case may be, the date on which the source of income newly comes into existence and ending with the said financial year.
Section 4 of Income Tax Act "Charge of income-tax"
Where any Central Act enacts that income-tax shall be
charged for any assessment year at any rate or rates,
income-tax at that rate or those rates shall be charged for
that year in accordance with, and subject to the provisions
(including provisions for the levy of additional income-tax)
of, this Act in respect of the total income of the previous
year of every person :
Provided that where by virtue of any provision of this Act income-tax is to be charged in respect of the income of a period other than the previous year, income-tax shall be charged accordingly.
(2) In respect of income chargeable under sub-section (1), income-tax shall be deducted at the source or paid in advance, where it is so deductible or payable under any provision of this Act.