A method and an arrangement (400) for determining an admission control threshold for use in an admission control procedure are provided. The admission control procedure manages a first spectrum resource (R1). The first spectrum resource (R1) has a first spectrum resource capacity and a first available spectrum resource capacity, wherein the first available spectrum resource capacity has a time dependence. In a step (220), the admission control threshold is determined based on the first spectrum resource capacity and a measure of the time dependence of the first available spectrum resource capacity.