miscalculation

mis·cal·cu·la·tion

miscalculation

n.
  1. a mistake in calculating.
  2. An error in judgment, especially about the effects of action or the likely course of events; as, IBM's miscalculation about the impact of microcomputers cost them many billions in lost opportunities; Sadam's invasion of Kuwait was only his worst, but not his last, miscalculation.