Both Planning and forecasting are basic and most important managerial activities. They are closely related to each other. Planning gives an answer to how, when, and what to be done.
It is a goal-oriented activity which designs a future course of action and provides a future environment of the organization.
As the future is uncertain, planners are forced to make some assumptions.
This assumption related to the future is called forecasting which is based on facts, past trends, economic conditions, and information.