Every person, if his total income . . during the previous year exceeded the maximum amount which is not chargeable to Income tax, shall furnish a return of his income . . . . (a) in the case of every person . before the expiry of six months from the end of the previous 692 year . , or before the 30th day of June of the assessment year, whichever is later; (b) in the case of every other person, before the 30th day of June of the assessment year: Provided that, on an application made in the pre scribed manner, the Income tax officer may, in his discretion, extend the date for furnishing the return (i) in the case of any person whose total income includes any income from business or profession the previous year in respect of which expired on or before the 31st day of December of the year immediately preceding the assessment year, and in the case of any person referred to in clause (b), up to a period not extending beyond the 30th day of September of the assessment year without charging any interest; (ii) in the case of any person whose total income includes any income from business or profession the previous year in respect of which expired after the 31st day of December of the year immediately preceding the assessment year, up to the 31st day of December of the assessment year without charging any interest; and (iii)up to any period falling beyond the dates mentioned in clauses (i) and (ii), in which case, interest at nine per cent per annum shall be pay able from the 1st day of October or the 1st day of January, as the case may be, of the assessment year to the date of the furnishing of the return (a) in the case of a registered firm or an unregistered firm which has been assessed under clause (b) of section 183, on the amount of tax which would have been payable if the firm had been assessed as an unregistered firm and (b) in any other case, on the amount of tax payable on the total income.