The ever increasing demand for high quality multimedia content in mobile networks requires the implementation of techniques for efficient spectrum management. Broadcast transmission is the preferred solution for scenarios in which the same content is transmitted to many users at the same time. The objective of this study is to propose an analytical method to calculate the user threshold to switch from unicast to broadcast in order to reduce radio resource utilization. We compute the probability of coverage of a given location in a Multicast Broadcast Single Frequency Network (MBSFN) area using tools from stochastic geometry. This expression is general and valid for a point not necessarily in the center of the MBSFN area. We use it to develop a method to calculate the user threshold analytically.