Critical path is identified with the use of Critical Path Method (CPM), which involves identifying:

  • Activity duration

  • Activity relationships (any relationship i.e. SS, FF, FS, SF)

  • Activities with zero Total Float (activities which can’t be delayed. If delayed, project end date will be effected)

This resultant critical path gives us the following:

  • Longest path (longest set of activities) in the project. In other words it gives us project duration
    Project end date.

  • Critical Path activities (activities that fall on Critical Path which also have zero Total Float)
    Early and Late dates of activities (detail in next slide)

When using Primavera or when learning project management, you might have heard about late start, ate finish. I will explain here the early and late dates to help you easily understand what these dates are:

Early Dates:

Let's say, the start date of my project is 1-January-2018.

The project has one activity (keeping the example simple). This activity can start on 1-January-2018.  The earliest date this activity can possibly start is 1-January-2018. This is the activity's early start date. Now, let's say the duration of the activity is 20 days. So if this activity starts on 1-January-2018, the earliest it will finish is 20-January-2018. This is its early finish date.

Late Dates:

Say the end date for my project is 30-December-2018.

My project has one activity only (again, keeping the example simple). The duration chosen for this activity is 10 days. Now, the latest date this activity will finish is 30-December-2018. This is the activity's late finish date. If this activity was to finish on 30 December, with 10 day duration,  the latest date this activity will start is 20-December-2018. This is the activity's late start date.

This is the simple definition of early and late dates in project scheduling. I hope you found their definition easy to understand.

In project scheduling, the late dates are usually not used by anyone. Someone might just want to know what the late dates of the activities are in case they need to start an activity as late as possible in the project and finish it as late as possible.

In Primavera P6 software, there are columns - early start, early finish and late start, late finish. You can add them. Once you have scheduled your project (by pressing F9), these columns will show you early and late dates for all activities.

What are project interdependencies? Activities in a project may need to be linked with activities in another project. Links between multiple projects is called project interdependencies.

Inter-project dependencies are categorized as either:

  • Dependencies:   These are the capabilities that the project requires from external sources in order to deliver successfully. E.g. task A from the other project will complete then we can start task 'xyz' in this project

  • Contributions:   These are capabilities that the project needs to deliver to external sources.

Activities are work to be performed. The project activities have the following characteristics:

Activity owner: a single person accountable for its performance. That person also reports progress on the activity.


Activity description: Name like ‘pour wall’ is self explanatory but some detail should be added such as ‘pour the east wall from top to bottom’.


Continuity of activity: Activity should represent continuous work. If any break to be added in activity, it is better to split the activity from breakpoints. 

Activity Start and Finish dates.

Activity Duration: Ideally, activity duration should be less than two times the update cycle. For example schedule is updated after every 10 days. The activity duration should be 5 or less. 

  • This is to allow reporting of the start and finish of the activity within one or two update cycles. 
  • This helps the management to focus on performance.
  • This is not applicable on Summary, Level-of-Effort (LoE) and Hammock activities.
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