The relevant sub sections of section 215 are: "215(1) Where in any financial year an assessee has paid advance tax under section 212 on the basis of his own estimate, and the advance tax so paid is less than seventy five per cent of the tax determined on the basis of the regular assessment (reduced by the amount of tax deductible in accordance with the provisions of sections 192 to 194, section 194A and section 195) so far as such tax relates to income subject to advance tax and so far as it is not due to variations in the rates of tax made by the Finance Act enacted for the year for which the regular assessment is made, simple interest at the rate of nine per cent per annum from the 1st day of April next following the said financial year up to the date of the said regular assessment shall be payable by the assessee upon the amount by which the advance tax so paid falls short of the said seventy five per cent.