SAP CRM :How to change the Date management Duration value at run time in BADI

Hi Frds,

How to update the date management duration value(number of month) in CRM_APPOINTMENT_BADI.

Example:

Duration = END date - Start Date.

When END Date manually change in Web UI--> BADI Trigger --> In Badi need to update Duration

Plese suggeste,

Thanks,

Rajan