Primavera P6 – Working with Negative Floats

 

Total Float (TF) and Free Float (FF) are two important concepts in Project Management. TF relates to the project’s overall finish date, while FF concerns the early start date of a successor activity. 

However, there is another type of float that is often overlooked: Negative Float (NF). In this post, we’ll explore how to work with NF in Primavera P6.

The content of this article is adapted from the Primavera P6 Pro Live Lessons course —a complete video program that includes detailed demonstrations and live examples on Negative Float.

Primavera P6 defines negative float as follows:

Negative float is when the total float is less than 0.0d.

You can learn more on negative float in this article. 

Now, considering Primavera P6:

• Negative float is, in fact, negative total float. It’s not negative free float.
• Though 0.0d (day) is informed, it can be 0.0 hour.

Find out the Negative Floats

In the below shown project, we have two activities with Start-to-Start dependency and without any lag. (Click on the image to enlarge) 

As shown:

• There are two activities “PRD Preparation” (5 days) and “PRD Approval” (2 days). 
• There is SS dependency without any lag between the two. 
• Notice the Early Start (ES) matches with the Late Start (LS). Early Finish (EF) matches with the Late Finish (LF). 
• As ES and LS as well as EF and LF match, the total float is zero.
• The formula for TF = LF – EF = 0.

Do note that Primavera P6 calculates the schedule options by taking LS and LF. 

Next, we introduced a lag of 2 days between the above activities, followed by leveling and scheduling. This resulted in the following. (Click on the image to enlarge)

As shown:

• There are two activities “PRD Preparation” (5 days) and “PRD Approval” (2 days). 
• There is SS dependency with a lag of 2 days. 
• Notice that the Early Start (ES) is greater than the Late Start (LS). Early Finish (EF) is greater than the Late Finish (LF). 
• The formula for TF = LF – EF = - 2 days.

This is reflected in the above figure.

Analyze the Negative Floats

One of the best ways to analyze the negative float is to use the forward and backward pass techniques. 

As noted earlier, we calculate the ES, EF, LS and LF and then find the TF value. Also, as noted earlier, Primavera P6 takes this default formula:

Total (TF)

= Late Finish (LF) – Early Finish (EF)

= LF – EF

In the first case (first figure), both LF and EF matches. Hence:

Total (TF)

= LF – EF

= 0

In the second case (third figure), EF is greater than LF by 2 days. Hence:

Total (TF)

= LF – EF

= - 2 days

Display the Negative Floats

To display negative float, you have to enable the bar settings, by clicking on the Bar Setting in the Tools toolbar. This is shown below.

 

After you apply the settings, the Negative Float Bar will be visible as shown in the below figure.  

As you can see now, now we have the negative float value coming for both the activities. 

Video Demonstration and Explanation

The below video [Duration: 3m, 55s] explains more on Negative Float (NF) with a live project. The live project is taken from the Primavera P6 Pro Live Lessons course.  

If you have a number activities and negative float occurs, it may not be restricted to one or two activities, but many! Hence, you need to be careful about the impact. This will not only impact the project’s schedule, but also cost/budget and understanding of the schedule.   

To have a better audio-visual experience, plug-in your earphones and go full-screen HD. 

Negative Float in Scheduling

Negative floats should always be avoided in a project schedule. If you notice multiple negative floats, it’s a clear sign that the schedule is not properly planned. Executing such a schedule is likely to result in significant problems during project delivery.

To resolve negative float issues, you should:

• Detect them early: Identify where negative floats occur in the schedule.
• Investigate the cause: Determine why they happened—common reasons include unrealistic deadlines, constraints, or misaligned dependencies.
• Enable visibility: It’s good practice to display negative float bars in Primavera P6 so they are easy to spot and monitor.

By addressing negative floats proactively, you can improve schedule reliability and reduce risks during execution.

References

[1] * NEW * Course – Primavera P6 Pro Live Lessons, with Full Money-Back Guarantee, by ManagementYogi.com 

[2] Course: Practical PMP with Oracle Primavera P6, by Satya Narayan Dash

[3] Course: Practical RMP with Oracle Primavera Risk Analysis, by Satya Narayan Dash

[4] Article: Critical Path Is Not Always the Longest Path! by Satya Narayan Dash