If one misses last date for advance tax payment

For a non corporate assesse, if he/she misses the last date for depositing the advance tax [15 March 2013];  I think, it still makes sense to deposit the same by 31 March 2013, because one saves interest of atleast one month.

My query is whether to deposit such amount [ between 16 march 2013 to 31 march 2013]  under the advance tax code or under the self assesment code because as per definition, tax paid before 31 march is an advance tax and not the self assesment tax. ?