In this paper, two approaches to calculating Capacity Factor of fixed speed wind turbines are reviewed and then compared using a case study. The quasi-exact approach utilizes discrete wind raw data (in the histogram form) and manufacturer provided turbine power curve (also in discrete form) to numerically calculate the capacity factor. On the other hand, the approximate approach employs a continuous probability distribution function, fitted to the wind data as well as continuous turbine power curve, resulting from double-polynomial fitting of manufacturer-provided power curve data. The latter approach, while being an approximation, can be solved analytically thus providing a valuable insight into the factors, affecting the Capacity Factor. Moreover, several other merits of wind turbine performance are based on the analytically derived equations and hence are an approximation as well. The note shows that the results obtained by employing both approaches are very close, thus the analytically derived approximations are valid and may be used for wind turbine performance evaluation.