Mortality among patients with various forms of sepsis is 36.2–47.7%. Predicting the likelihood of death associated with sepsis is critically important for clinical decision-making, stratifying patient risk, and improving overall survival. The study aimed to develop a mathematical model for predicting the outcome of sepsis in patients with abdominal surgical pathology. The study involved 64 patients diagnosed with abdominal sepsis (AS). Based on the AS outcomes, group 1 (n = 46) with favorable outcomes and group 2 (n = 18) with fatal outcomes were allocated. Clinical scales and laboratory testing methods were used to evaluate parameters on days 1, 3, and 7 since the AS diagnosis. On days 3 and 7, SOFA scores of the group with adverse AS outcomes were significantly higher, than that of the group with favorable outcomes. Complete blood counts of patients in group 2 showed the decrease in absolute lymphocyte counts on day 1 compared to group 1. As for blood biochemistry parameters, elevated serum levels of C-reactive protein, urea, creatinine, lactate, procalcitonin, direct bilirubin, as well as aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activity were observed. Furthermore, a decrease in respiratory index on days 3 and 7 and venous oxygen saturation on days 1 and 7 was observed.  A logistic regression model was constructed, and a software tool "Calculator for Predicting Mortality in AS" was developed. A model to predict the probability of fatal outcome in patients with AS was created. High serum CRP and creatinine levels, as well as the decrease in venous oxygen saturation serve as significant prognostic markers of fatal outcome in patients with AS.