While wind assessment periods commonly range from 1 to several years, this is typically based on experience and industry norms. In this investigation, we perform an analysis of the error that can be expected in a wind resource assessment of various lengths of time. In contrast to earlier work measuring the uncertainty of predicted wind speeds, the uncertainty in this evaluation is measured directly in terms of energy and revenue production. As the wind assessment period increased from 30 days to 1 year, the average error increased slightly. However, when the wind assessment period was increased to 2 years, the average error decreased significantly. Simultaneously, the standard deviation of the error distributions decreased and the magnitude of the maximum experimentally obtained error decreased. By understanding how the energy production uncertainty decreases with increasing assessment time, the length of the assessment period can be tailored to match a developer’s risk tolerance.