The paper discusses the problem of reliability calculation for mechanical units under load. Because the rated reliability of the unit as a system with many independent elements can tend to zero, the methods of reliability calculation of the units as real objects with the common factors (loads, operation conditions) are proposed. The choice of the life test modes and test time depends essentially on unit-related information like their operation conditions. The paper describes one of approaches, passing to this problem. Within its framework, the accumulations of damages are made at several typical points of the loaded system.