Nowadays, accuracy of definition final the settlement of buildings and structures erected on soft clay soils is very important, because settlement of buildings developing for decades and difficult predictable. Current work carried out comparison of the most common engineering and numerical methods for calculating the final settlement of buildings with the results of long-term field observations. Comparisons are based on monitoring of two historical buildings that are located in one area at the Saint-Petersburg. The quantitative results are obtained and conclusions about the applicability of different theoretical methods for calculating the settlement are made. Also concluded need of long-term field observations, due to further development of rheological models could be more accuracy.