The article presents a method of mathematical computer analysis of the state of the main regulatory system of the body - the autonomic nervous system in patients with thyroid diseases. A formula has been proposed that allows one to calculate the severity of impairments in the regulatory system and the degree of stress (depletion) of adaptive mechanisms - a single vegetative index (SVI). Using the method of computer modeling, the boundary values of this indicator were determined and the effectiveness of its use was tested on a group of patients (26 people) diagnosed with thyroid diseases. The results obtained confirmed the effectiveness of using the method, both for assessing the current state of the body, and for determining the safety of the functional reserves of the body and predicting the course of the disease. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.