i am having difficulties with my formulas . 
I am trying to acheive the following:  
IF status row is not "complete" AND  due date is Today or in the past, if true Flag,  if not unflag. 
My formula is:
=IF(AND(Status28 <> "Completed", [Planned Finish]28 >= TODAY(-15)), 1)
However this is the results - it is not calulation what i want it to show.  What am i doing wrong or what have i missed?