Back to Basics: The Relationship Between Activity Types and Calendars

Written on . By CPM Solutions

Often times, we have students come into our class confused as to why their activity finish dates are changing or not changing when they reschedule the project. It usually takes some digging around, but it always leads to the same answer – calendars. Calendars have a huge effect on how long your activities (and project) take to complete.

Primavera has different types of calendars to accommodate real-life scenarios. Sometimes activities can be completed based on a regular work schedule, but some might be dependent on a specific resource’s availability to come onto a worksite to perform a task. So, when you find that your schedule looks differently than you initially thought, take a good look at your assigned calendars.

The next question is: If there are so many calendars, which should I be looking at? The calendar you should be using to interpret the results of the schedule depends on the Activity Type assigned to each individual activity. The activity type determines which calendar(s) is/are used while scheduling.

“Together, the activity type and assigned calendars affect how long your activity and project will take to complete.”

There are two activity types that will significantly change how your activities are scheduled: Task Dependent and Resource Dependent. These two activity types use different calendars to calculate the duration of your activity.


A Task Dependent activity uses the assigned project calendar to determine the length of the activity. It does not take into consideration the assigned resources’ calendars when scheduling the activity.

There are two locations to check which calendar is assigned to your activity:

Location 1: Projects window, Defaults tab

  1. Open the Projects window by clicking the Projects folder icon on the directory bar on the left hand side.
  2. Click on the layout drop-down menu and select Show on Bottom, Project Details.
  3. Click on the Defaults tab. 


The calendar assigned at the project level is used as the default calendar for all new activities. But, you can change this calendar at the activity level, to individually customize your tasks as well.

Location 2: Activities Window, General Tab

  1. Open the Activities window by clicking on the Activities icon (green bar on the left hand side, directory bar).
  2. Click on the layout drop-down menu and select Show on Bottom, Activity Details.
  3. Click on the General tab


The calendar assigned at the activity level determines how a Task Dependent activity is scheduled. In this example, the calendar is the same at the project and activity level. This may not always be the case! Primavera P6 allows you to change the calendar at the activity level for complete customization.

Tip: Customize your columns in the Activity Table to view your Activity Type and Calendar side-by-side. This will help you to quickly assess which activities or calendars are affecting your project completion.


A Resource Dependent activity uses the individually assigned resource calendars to determine the duration of the activity. The Finish Date of the activity will be based on the time required by the last resources it will take to finish the same task, based on their own calendars. It can become trickier and cumbersome to understand why a Resource Dependent activity has a specific duration if you have multiple resources assigned to an activity at one time.

There are two types of Resource Calendars:

  • Shared Resource Calendar, where one or more resources are assigned to the same calendar.
  • Personal Calendar, where one resource has a customized calendar specific to their schedule.

To check which calendars are assigned to your resources, you’ll have to go to the Resource Dictionary, Details tab:

  • In the Activities window, note which resources are assigned to the activity.
  • Open the Resources Dictionary by clicking on the Resources icon (person icon on the left hand side, directory bar).
  • Click on the Details tab. Check the assigned calendars.

You can change the assigned calendar for each resource in your Resource Dictionary. You can create a Personal Calendar in the Details tab for the selected resource, use an existing Resource Calendar, or assign a Project Calendar.


If you’re unsure why your activities are finishing later than expected, follow these quick steps:

  • Check your activity type.
    • Tip: Check to see if you have any assigned constraints.
  • Check your assigned activity/resource calendars based on the activity type.
    • Task Dependent activity = Activity Calendar.
    • Resource Dependent activity = Resource Calendars.
  • Determine which calendars are affecting the activity finish dates and project completion date.