What is Project Slack?

Slack is the difference between the scheduled completion date of a task and its required date, where the required date is later than the completion date. When there is slack in a task, a project manager can choose to delay the start of the task, allocate fewer resources to it, or conduct the task in the usual manner and preserve the slack in case there are delaying problems later in the project. There is no slack in the critical path of a project, which is the sequence of activities that determine a project’s minimum possible duration.

Example of Project Slack

A company is launching a new e-commerce website. The project consists of four tasks, each with a defined duration:

Task A: Design wireframe. 5-day duration, no predecessor task.
Task B: Develop website backend. 10-day duration, Task A is the predecessor task.
Task C: Write content. 7-day duration, Task A is the predecessor task.
Task D. Test and deploy. 4-day duration. Tasks B and C are predecessor tasks.

Step 1: Identify Critical Path

The critical path is the longest sequence of dependent tasks that determines the shortest possible project duration. This calculation is as follows:

Path 1: A → B → D= 5 + 10 + 4 = 19 Days (Critical Path)
Path 2: A → C → D = 5 + 7 + 4 = 16 Days

Since Path 1 (A → B → D) takes 19 days, it is the critical path, meaning these tasks have zero slack (any delay will delay the project).

Step 2: Calculate Project Slack for Task C

Task C (Write Content) is not on the critical path, so it has slack. The slack for Task C = Critical Path Duration - Path 2 Duration, which is three days. This means that Task C can be delayed by up to 3 days without affecting the overall project deadline.