Dear Mahesh,
Delay calculation depends on basic start and finish date
please check your basic date for activity, network and wbs,
Delay:-
For network/order:
Today's date minus basic finish date
For network activity:
Today's date/time of shift begin minus latest finish date/time of activity.
For WBS element:
Today's date minus latest finish date/basic finish date
Later :-
For the network plan/order:
Actual finish date minus the basic finish date
For a network activity:
Actual finish date minus the last finish date
For a WBS element:
Actual finish date minus the last finish date or basic finish date
Regards
Deepak