How To Find Head Slack In Cpm

How To Articles

As a project manager, one of the key aspects of my role is to effectively manage project schedules. Critical Path Method (CPM) is a popular technique that helps in this regard by identifying the critical path and determining the project’s duration. Along with the critical path, another important consideration is head slack, which allows me to assess the flexibility of non-critical activities. In this article, I will dive deep into the topic of head slack in CPM and share my personal insights and commentary.

Before delving into head slack, let me provide a brief overview of CPM. CPM is a project management technique that determines the longest path of activities in a project. Activities along this path are critical and any delay in their completion will delay the entire project. By identifying the critical path, project managers can focus their attention on these activities and allocate resources effectively.

Now, let’s talk about head slack. Head slack refers to the amount of time by which a non-critical activity can be delayed without affecting the project’s overall duration. In other words, it represents the flexibility available for these activities.

To find head slack in CPM, we need to follow a series of steps:

  1. Identify the critical path: Before finding head slack, it is crucial to determine the critical path. This can be done by analyzing the network diagram and calculating the duration of each path.
  2. Determine the non-critical activities: Once the critical path is identified, we can easily distinguish the non-critical activities. These are the activities that are not part of the critical path and have some flexibility in terms of their start and finish dates.
  3. Calculate the total float: Total float is the amount of time by which an activity can be delayed without delaying the project. It can be calculated by subtracting the earliest start date of an activity from its latest start date or the earliest finish date from its latest finish date. The total float represents the amount of time available for an activity to be delayed without affecting the project’s duration.
  4. Analyze the head slack: Once the total float for each non-critical activity is determined, we can identify the activities with positive total float. These activities have head slack and can be delayed without impacting the project’s duration.

Now, let me provide some personal insights and commentary on head slack in CPM. I believe that head slack plays a crucial role in project management as it offers flexibility in managing non-critical activities. It allows project managers to prioritize resources and allocate them to critical activities while still maintaining control over non-critical ones.

In my experience, head slack can be a valuable buffer that helps in dealing with unexpected delays or changes in project scope. By utilizing the head slack effectively, project managers can minimize the impact of delays and ensure that the project stays on track.

However, it is important to note that head slack should not be taken for granted. While it provides flexibility, it is still essential to closely monitor non-critical activities and ensure that they are completed within the allocated time. Ignoring non-critical activities or excessively relying on head slack can lead to potential risks and delays.

In conclusion, head slack in CPM is a significant concept that allows project managers to assess the flexibility of non-critical activities. By understanding and utilizing head slack effectively, project managers can successfully manage project schedules, accommodate changes, and deliver projects on time. Remember, while head slack provides flexibility, it should be managed carefully to avoid any potential risks or delays.


Head slack in CPM provides project managers with the flexibility to manage non-critical activities without impacting the overall project duration. By accurately identifying the critical path, calculating total float, and analyzing head slack, project managers can allocate resources effectively and prioritize activities to ensure successful project delivery. However, it is essential to remember that head slack should be used judiciously and monitored closely to avoid potential risks. With a thorough understanding of head slack, project managers can confidently navigate through complex projects and deliver results.