Interest u/s 234A is to be calculated if the payment of the tax is after the due date of filing the returns [as mentioned for the particular assessee u/s139(1)] @ 1% per month on net tax payable(after TDS Deduction).
Interest u/s 234B is to calculated if the payment of tax is after the last day of the previous year @ 1% per month on the net tax payable.
Interest u/s 234C is to be calculated if the advance tax hasn't been sufficiently paid within the due dates.
Due dates and the amount required to be paid for
Companies
June 15th - 15% of Net tax
Sep 15th - 45% of net tax
Dec 15th - 75% of Net tax
March 15th - 100% of Net tax
Other assessees
Sep 15th - 30%
Dec 15th - 60%
Mar 15th - 100%
If the advance Taxes are not paid within the due dates,
then for the deffecient amount interest will be charged at 1% per month
i e , 3% for all the defeciencies upto march
and for the defeciency in march advance tax has to charged @ 1% only