How to Validate Input is greater than already Exists date in

Question

Hai Friends,
      I m creating one application in that i wanna validate the input date.
i.e
 i m my application input fields are
date:(jquerydatepicker)
from:(text)
to:(text)
numberofdays:(text)
add(button)
after given the enitre details ll show on gridview and i put one condition date ll be display on depends given numberofdays and put disable mode.
when i close the application and again start the application its accepts less than dates.
ex:
5th may-13 numberof days=2 add
ll show 10th may-13 on inputdate now i close the app and again start the app now i m enter 4th may -13 numberofdays=3 add it ll accpeted....
i need validate input is alws greater than gridview already appeared date.