The goal of this study is to identify and evaluate the connection between the Gregorian and Hijri calendars. The paper aims at identifying how the interaction between both calendars can be used for good business forecasting. Aspects will include how the interaction increases or decreases demand. The factors of demand will be highly dependent on the events taking place in the two calendars. For example, the Hijri calendar is usually followed by the members of the Islamic faith. These events influence the way demand forecasting is done. For instance, Ramadan is a special holiday within the Hijri calendar where members of the Islamic faith are required to fast for a specific period. During this period, the demand of products offered by a business will decrease, mainly during the day when they are not required to eat. When forecasting demand, several elements have to be considered among them an organizations staffing. Furthermore, the main events in the two calendars affect demand positively as well as negatively. When preparing for festivities, the demand for business products may increase. All the same, some of the effects are adverse such as the traveling of employees during the festivities, which results in the organizations being understaffed. Several examples are provided in the article showing some of the factors that influence business forecasting Also, explained are the various steps that are used when transforming the Gregorian information into the Hijri system considering the overlapping of the holidays in Islamic countries.