GOST R 54257–2010 recommends calculating the reliability of the earth foundations of structures by probabilistic methods with full statistical information about random quantities. Currently, there are no guidelines for calculating the reliabilityof earth foundations by the settlement with limited information about the parameters. The earth foundation (foundation bed) is a part of a mechanical system also including the foundation itself and the above-foundation construction. One of the indicators of the safety of this system is the probability of non-failure, where the probability of non-failure of an earth foundation is included. In this article, we discussed a new method for calculating the reliability of earth foundations of buildings and structures during the operation stage according to the deformation criterion with limited information on the soil and loads by using Zadeh’s extension principle from fuzzy sets theory. The article presents formulas and an example of an algorithm for calculating earth foundation reliability by the settlement criterion.