(1) Where an assessee commits default in making the payment of any amount of tax leviable or payable or of any amount of tax. interest r penalty assessed or determined or of any amount or demand otherwise payable, within the specified time under the provisions of this Act or the rules made or notifications issued thereunder, such assessee shall be liable to pay interest on such amount at the rate of 15 per annum or part thereof, for the period starting from the day immediately succeeding the date specified for such payment and ending with the day on which such payment is made. (2) Interest under sub-section (1) shall be calculated- (a) at the time of assessment under any section or in continuation of such assessment; and (b) on payment including adjustment of a demand in full.