Hi Julie
Many thanks for your prompt response (yes I did spell the Function name wrong :-)).
I ended up using this formula in the end but will also try your solution:

IIf([Finish]>Date(),IIf([Finish]-Date()<=3,"TRUE","FALSE"),"NA")

Edit:
I modified your solution in an attempt to ignore those tasks that were complete but the edit does not work, any ideas?

IIf([Status]="Complete","",IIf(DateDiff("d",[Finish],[Current Date])>0 And DateDiff("d",[Finish],[Current Date])<=3,True,False))

Thanks

Tony