Since self assessment tax is not mentioned in above, interest was being calculated on self assessment tax paid by assessee before due date of filing of ITR.
Now, vide circular 2/2015 dt. 10th Feb-15, IT dept. has asked its officer not to charge interest on self assessment tax paid before due date of filing of ITR. This decision of IT Dept. is based on the judgement of Supreme Court in the case of CIT vs Prannoy Roy, 309 ITR 231 (2009) where court has held that interest is chargeable after deducting self assessment tax paid before due date of filing.
Complete text of circular can be downloaded from here.