The article examines five South Slavic copies from Brontologion from the Late Middle Ages (16th–18th centuries), which are combined prognostic works. They contain the most numerous and detailed depictions of astronomical and meteorological phenomena. Also, through the text of prognostication works, data on the everyday life and lifestyle of medieval man can be found. These copies testify to the change in their social function. Initially, they were read in the royal and boyar courts. Because of the historical changes in the Balkans and the fall of Bulgaria under Turkish slavery, prognostication began to spread to the broader layers of society through the mediation of the lower clergy. Changes also occur in the language and structure of the text.