The network diagram has floats of two types. They are total float and free float. These two floats are crucial in creating a network diagram. Understanding these better will enable you to draw one and examine a critical path.

Let’s begin with total float.

Total Float

It is also called a “float”. Total float means how long we can delay an activity without taking off the completion date of the project.

The total float will be zero on the critical path. It is usually known as slack.

It can be calculated by subtracting the activity’s Early Start date from the Late Start date.

Total Float = The Late Start date – The Early Start date

Or

You can calculate by subtracting the Early Finish date of the activity from the Late Finish date.

Total Float = The Late Finish date – The Early Finish date

Free Float

It means how long we can delay an activity without delaying its successor’s Early Start.

It can be calculated by subtracting the current activity’s Early Finish date from the next activity’s Early Start date.

Free Float = The Early Start date of the Next Activity – The Early Finish date of the Current Activity.

Also, note that if both activities merge, then only one among these two will include a free float.

A remark on the convention applied in the example

The project’s first day can be referred to in two ways. Some consider it as “one” and others as “zero”.

Both of these conventions are right and you can choose any. But it is better to refer to the project’s first day as “one”. Below are the reasons for choosing it:

  • The PMBOK Guide obeys this convention.
  • It appears logical to say that today is day one of the project rather than saying today is day zero of the project.

However, you can listen to your preference.

The formula that is used to estimate a free float differs for both of these situations.  Yet, the result remains the same.

I’m presuming that you figure out how to draw the network diagram, recognize the crucial path, and estimate the activity’s Early Start, Late Start, Early Finish, and Late Finish dates.

Summary

Free Float and total float are vital notions in schedule management. Activities that are in a non-critical way contain a total float. Total float is generally known as float. When two of the activities converge, one among them will include a free float.

Please notice that the total float has to be found out if they ask you to estimate the float for an activity in the exam.