Abstract: A Femtocell (FMC) is a low power cellular home base station, which is low in cost and operating in licensed spectrum. Nowadays, because of the requirement for high data rate and large area coverage indoors, FMC provides the solution to these requirements. FMC is deployed mainly indoors and sometimes outdoors at the cell edge to increase the area of coverage, capacity and in order to enhance the received signal in the user’s premises. In this paper, a novel technique and a Monte Carlo simulation is implemented to calculate the interference, the SINR and the probability of connection at the downlink for a varied number of FMCs based on LTE and WiMAX OFDMA range. Moreover, a novel Monte Carlo simulation is used to carry out the comparison of interference, SINR and probability of connection for three different numbers of FMCs. Furthermore, a novel comparison of FMCs at various SINR threshold values is presented. The downlink interference occurs from neighbouring FMCs to the target user equipment (UE) when the signal transmits from the serving FMC to the target UE and the signals which are transmitted from the neighbouring FMCs would have the same subchannels during the downlink transmission. This paper will explore the appropriate number of FMCs that could serve a specific indoor area and the proper number of UEs in the specified area. Keywords: Femtocell, Home Base Station, Interference, SINR, User Equipment, Indoors, Downlink.