how to add two date format in web i report.

Hi Every One,

                 I have Fields like Start Date,New Date, Close Date, End date balance.

that Fields all are in date format like start date(05/05/14), New date(06/05/14),Close date(09/05/14)

But i need result (start date+new date)-close date=enddate balance .

How will achieve this requirement in web i please replay me.