Under these section interest is levied on the amount being unpaid as advanced tax in the previous financial year As there are 4 dates on which advance tax shall be paid which are as follows 15 june=15%of advance tax must be paid 15 September =45%of advanced tax must be paid 15 dec=75% of advance tax must be paid 15 March =100% of advance tax must be paid If the assesse fails to pay the amt. as specified above on or before the due dates interest is levied on them under section 234C @ 1%per month And time period for calculating interest is 3 months for June, September, December late paying and 1 month for March it's fixed, i.e. it doesn't depends upon on which date u paid the tax