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 all time-based aspects of a project, such as, schedule dates and duration, estimated effort, and resource allocation dates.

A project calendar is based on a base calendar that is maintained in Application Administration. During project creation, you select a base 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. You can modify the project calendar to suit the project requirements by adding or modifying the calendar exceptions. An exception refers to a day that is designated as non-working, or a day with reduced, special, or extended working hours. A project calendar is 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. Project elements such as tasks do not have their own calendars, distinct from the project calendar.

It is mandatory to select a calendar from the available base calendars during project creation. By default, the Default Calendar is selected as the project calendar for a new project. You can modify this selection before you save the new project. After you save the project, you cannot modify the calendar selection. However, you can modify the calendar exceptions.

Project schedules are calculated based on the project calendar.

For example, 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 project calendar and its impact on project schedules - this is to be decided - this section is work-in-progress

Changes to the base calendar made at any time are also reflected in the project calendar. You have the option to override the base calendar modifications.

When you modify a project calendar by modifying the exceptions, or when a base calendar is modified, any newly created project elements are calculated based on the modified calendar information. Existing schedules are not recalculated.

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.
Related concepts
Base calendar
Related tasks
Creating a project
Creating a project WBS
Customizing the project calendar

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