Because of the random nature of user mobility, the channel gain of each user in a cellular network changes over time causing the signal-to-interference ratio (SNR) of the user to fluctuate continuously. Ongoing connections may experience outage events during periods of low SNR. As the outage ratio depends on the SNR statistics and the number of connections admitted in the system, admission capacity planning needs to take into account the SNR fluctuations. In this paper, we propose new methods for admission capacity planning in orthogonal frequency-division multiple-access (OFMDA) cellular networks which consider the randomness of the channel gain in formulating the outage ratio and the excess capacity ratio. Admission capacity planning is solved by three optimization problems that maximize the reduction of the outage ratio, the excess capacity ratio, and the convex combination of them. The simplicity of the problem formulations facilitates their solutions in real time. The proposed planning method provides an attractive means for dimensioning OFDMA cellular networks in which a large fraction of users experience group-mobility.