Time is one of the limited and valuable resources that it's planning and proper allocation is a controversial issue in every educational system. It is impossible to plan and present an appropriate academic calendar unless the related influential factors are identified analyzed and applied. The research question is: What are the effects of climate, educational, social, and economic circumstances on high school academic calendar? The research method is descriptive and its statistical population includes three groups of Isfahan and Yazd high school teachers, principals and district administrators. We selected 180 teachers through a two - stage random sampling, and principals through a simple random sampling. We used a questionnaire to gather the quantitative data from the sample of principals and teachers. In order to collect qualitative data, we used semi-structured interviews with district administrators. Quantitative data were analyzed in two statistical levels- descriptive and inferential – using SPSS software and qualitative data were analyzed with the classifying method. Research findings showed that climate, educational, social and economic conditions are fundamental factors that should be considered by decision makers in adjusting educational time and preparing an academic calendar. The intensity and degree of the effects of each condition varies according to the region. These effects require further research.