The paper presents the results of a computational study of the effect of the longitudinal pressure gradient (PG) on the position of the laminar-turbulent transition (LTT) in the boundary layer on a smooth plate and on a plate with local surface irregularity. For a smooth plate, the calculations were performed using both the method developed by the authors, based on the Global Stability Analysis (GSA) of the laminar boundary layer, and other known methods that take into account the LTT. The results obtained varied significantly for different methods and differed from the more reliable GSA results, which questions the accuracy of these methods. The studies have proved that it is possible to perform a total evaluation of the LTT position shift by adding the shift for a smooth plate due to changes in the PG value and the shift for a plate with irregularity on its surface in the absence of PG.