A project calendar is based on a calendar that is created and maintained by your project management administrator as project administration data. During project creation, you select a calendar that best matches the project environment. An instance of the base calendar is created and linked to the project, and this is referred to as the project calendar. The project calendar contains all the attributes of the base calendar, such as the start and finish dates, working hours per day, and the exceptions. An exception refers to a day that is designated as non-working. You can modify the project calendar to suit the project requirements by adding new exceptions. A project calendar is thus a combination of the exceptions defined in the base calendar and those defined in the project calendar.
A calendar can only be associated at the project level and is applicable for all project elements, including subprojects. Subprojects, and project elements such as tasks, cannot have their own calendars, distinct from the project calendar.
It is mandatory to select a calendar from the available calendars during project creation. After you save the project, you cannot modify the calendar selection. However, you can create your own exceptions for the project calendar.
Project schedules are calculated using the exceptions, and the work hours per day defined in the project calendar.
Modifying the base calendar and its impact on project schedules
Changes to the base calendar made at any time are also reflected in the project calendar.
When you modify a project calendar by adding a new exception, or when a base calendar is modified, any newly created project elements are calculated based on the modified calendar information. The schedule of existing work items are not recalculated till you modify and save the schedule of the existing work items. When you modify the schedule of the existing work items, the schedule is recalculated using the modified calendar information.