An experimental theoretical method was considered for estimating the residual load-bearing capacity of an individual reinforced concrete beam at the operational stage according to the criteria of the working strength and durability of concrete reinforcement compressed zone of the beam. Integrated methods of beam testing and probabilistic methods of random variables definition were used. Ultimate load in the form of interval during the operational phase was accepted as the measure of carrying capacity, discussion is presented on the choice of its value obtained from the interval boundary that has been obtained. Transition from the experimentally obtained value of the ultimate load to the maximum operational load was studied. Examples of design models of beams with operational load and guidelines on how to determine their limit values were given.