How many days in a year did the medieval knights have to serve in the army?

Medieval knights were typically required to serve in the army for a period of around 40 days each year during times of war. This service was often stipulated by the feudal system, where knights owed military duty to their lords in exchange for land and protection. However, during times of prolonged conflict, knights could be called upon for extended periods beyond this standard. The exact number of days could vary based on the specific obligations set by their lords and the nature of the conflict.