Project calendars

A project calendar contains a record of working and non-working days and hours for a project, and provides the basis for calculating the time-based aspects of a project, such as schedule dates and duration, and effort.

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.

Note: In the project calendar, you cannot modify the exceptions inherited from the base calendar. You can only add new exceptions.

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.

When you assign a start date and end date to a task, the duration of the task is calculated based on the actual working days and hours available between those dates in the project calendar. Consider a task with a constraint type 'As soon as possible', for which you enter the start date as 1 September 2008, and the end date as 26 September 2008. The project calendar for this task has Saturdays and Sundays as weekly holidays and there are no other holidays (exceptions) in the calendar during the specified dates. In this scenario, the duration of the task will be calculated as 20 days. Further, if the project calendar specifies 8 working hours per day, the total effort for the task will be 160 hours.

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. 

If you modify the same project calendar by declaring 26 September 2008 as an exception (non-working) and reduce the working hours per day to 7, then the end date of the task will be 29 September and the total effort for the task will be 140 hours.

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