The authors present a method for predicting the long-term deformation of materials based on the base diagram concept. The long-term strength calculation of steels 18Cr-12Ni-Mo and 21Cr-32Ni-Ti-Al for different specified stress and temperature values showed the efficiency of its defining relations. The advantage this approach has over the most common parametric methods such as the Larson-Miller, Orr-Sherby-Dorn, Manson-Sakkop, and Trunin parameters is shown.