Mr Nikhil , you can file belated return u/s 139(4).
After Filing the return you cannot revise the return u/s 139(5).
Suppose your tax liability is below Rs. 10,000 then Interest u/s 234B and 234C will not be applicable.
whereas interest u/s 234A will apply @ 1% on the amount payable from due date of iling of return if 31-07-2011 then from August 2011 till you file your return , if Jan 2012 then Aug to Jan 2012 6 Months.
And if Sept 2011 is due date then 4 Months.
Suppose your tax liability is above Rs. 10,000 then Interest u/s 234B and 234C will also be applicable.
Interest u/s 234A as above.
Interest u/s 234B @ 1% from April 2011 to Jan 2012 (if return filed in Jan 2012)
Interest u/s 234C would be as under:
Rate Due on Interest on Tax
30 15 Sept Tax @ 30% @ 3%
60 15 Dec Tax @ 60% @ 3%
100 15 Mar Tax @ 100% @ 1%
Rate Due on Interest on Tax
15 15 June Tax @ 15% @ 3%
45 15 Sept Tax @ 45% @ 3%
75 15 Dec Tax @ 75% @ 3%
100 15 Mar Tax @ 100% @ 1%
So the more you delay the more you pay interest @ 2% per month from now on as interest u/s 234A and 234B.
Further as per Income Tax Act if amount paid is short then the same will first be adjusted towards interest and then the balance towards tax.
So be careful.