Issue comparing date field in report builder 3.0

List below is my expression:

=IIf((Fields!TaskActualFinishDate.Value Is Nothing), " ", IIf(format(Fields!TaskActualFinishDate.Value, "MM/dd/yy") > format(Fields!TaskDeadline.Value, "MM/dd/yy"), 0, 1))

But it seems like only the Month and Date fields are been compared not the hold date field MM/DD/YY. Can someone please tell me what I'm not doing correctly thank you so much.