The beam-column connection is an important structural element in frame structures. For the past six decades, it has held the interest of scientists with its vulnerability during the seismic impacts. Shear forces, which are not fully understood, have been cited as responsible for a number of building failures in earthquakes. In the current codes, these forces are determined capacitively based on the amount of inserted in the beam-column connection reinforcement. However, this does not answer the question of how large the shear forces actually are. In the present paper, a cantilever beam loaded with a linearly distributed load with intensity at the free end of the beam is considered. The full dimensions and mass properties of the beam materials are taken into account. Expressions are derived for the magnitudes of the resulting support reactions, corresponding to the reinforcing bars and the concrete support. A limit stage was considered, which makes it possible to track the changes in the values of the support reactions both before the appearance of a crack between the beam and the column, and during its growth. Expressions are derived for symmetric beam cross-sections. The shear force value at the beam-column joint was calculated based on the exact values of the beam forces. The results are compared with those recommended in the literature. A comparison has been made with Eurocode. The proposed exact method gives results that differ from the adopted in the literature by 5.47% to 21.53%, depending on the stage of crack development. The difference between the new exact method and that of the Eurocode ranges from 1.31% to 16.97%, based only on the largest shear force value determined by the exact method.