SQL Date Duration between two Dates

Declare @Fromdate datetime
Declare @Todate datetime
Declare @TopID int
Declare @Duration int


Select top 1 @TopID= LeaveId from dbo.LeaveDetails order by LeaveId desc


select @Fromdate= convert(varchar,FromDate,103) from dbo.LeaveDetails  where LeaveId=@TopID


select @Todate = convert(varchar,ToDate,103) from dbo.LeaveDetails  where LeaveId=@TopID


SELECT @Duration=DATEDIFF(dd, @Fromdate,@Todate)