Together with the developing technology, the demand for electrical energy is increasing day by day. Due to the increase in energy demand and the difficulties in creating new transmission lines, power systems are forced to work in areas close to stability limits. If the power value expressed as the voltage stability limit is exceeded, the voltage stability of the system will be impaired. In this case, the maximum power value that the load can demand from the system, the maximum power value that can be transported from the transmission lines and the minimum limit values that the voltage amplitudes of the load busbars can descend must be known. These values, also called critical values, are the voltage stability limit values. In this study, 5 bus system was chosen as an exemplary power system. PowerWorld program was used in this simulation study. The maximum power values that can be drawn from the load busbars are calculated by two states, the constant and variable power coefficient of the 254 demand power, and the voltage collapse estimation index (VCPI). Theoretically, the maximum power value that can be drawn from the system is calculated by the power transfer stability index (PTSI). According to the data obtained, the maximum power values that can be drawn from the load busbars in the power system are compared with the results of two different index values. When calculating the critical power values that can be drawn from the load busbars, the combination of these two indices increases the accuracy and reliability of the calculated critical power values. An analysis was made that the loads could draw power from the system as much as the critical power value, and after this critical power value, the system would collapse.