Controlling medium access priorities in wireless networks is difficult when multiple radio stations operate according to the popular IEEE 802.11 contention-based protocol. Although the new standard 802.lie defines enhancements for controlling priorities in this distributed medium access control protocol, it does not provide algorithms for the calculation of the achievable throughput per station, when different stations operate with the different priorities. Such an algorithm is discussed in this paper. The evaluation by means of simulation indicates that the algorithm approximates the achievable throughput in many different scenarios.