Five Things to Know About Critical Path

Critical path refers to the sequence of activities that must be completed on time for the entire project to be completed on time. It is an important aspect of your project schedule. Here are five things to know about critical path.

1. Float refers to schedule flexibility

On every project, no matter how complicated, there are always some activities that can be started earlier or completed later without jeopardizing the final completion date. This flexibility between the earliest time an activity CAN be completed and the latest time when it MUST be completed is called "float".

2. The critical path has no float

Now let’s look at those activities where you do not have the flexibility in the start and end-dates. These activities cannot be completed earlier because they are pending the completion of another activity. They also cannot be completed later without causing all the succeeding activities to be late. All of these activities back up tightly against other activities that precede or succeed them. In other words, the path has zero float.

The critical path consists of the longest sequence of activities that must be started and completed exactly as scheduled. It is the longest sequence of activities with zero float.

3. Why is the Critical Path Important?

If the project is trending late it is very important to identify the critical path activities. Unless you are able to accelerate activities on the critical path, the end-date for the entire project will not change. Applying additional resources to activities that are not on the critical path will not affect the overall project end-date. Your chance to make an impact on the projected end-date relies on your ability to identify and shorten the critical path.

4. The Critical Path May Change

Given that there are many, many paths through the schedule, it’s possible for the critical path to change. For instance, say you have a project with 22 activities over nine months. Let’s assume that there is another path of work that includes 19 activities and takes 8 ½ months. There are two weeks of float on this path. Let's say one of the activities on the 8 ½ month path ends up taking an extra four weeks. Because there was only two weeks of float in the path, it will now become the critical path and force the entire project to complete in 9 1/2 months.

5. You must sequence activities to understand critical path

The critical path relies on an understanding of the successors and predecessors of each activity. If your activities are not sequenced, the critical path may be calculated erroneously.