I got to know about this in august as well, While filling my ITR..
But this is weird.. they are calculating percent based on tax liable on 31st March even expecting to pay 100% taxes till 15th March...
Also, What if someone is getting large amount bonus of 10L on 31st March, which will have tax around around 3L... He can pay 3L straight forward on 31st March.. But still he has to pay quarterly interest on 15%, 45% and 75% of 3Lakhs...
I think they should compute based on amount earned and tax paid each quarter.. instead of computing based on full tax liability and dividing using some random percentage figures of 15, 45 so on...