Eliminate the Confusion: Understanding the Peak Field

The 2010 version of Microsoft Project introduced some new functionality whose behavior has confused and confounded users with all degrees of experience, from absolute beginners to power users. Microsoft introduced this new functionality to fix a bug that had been present in the software since I first started using it many years ago. When Microsoft released Project 2010 in beta form, I confirmed that they did fix the bug, but I noted that new behavior in the software would probably confuse people. Of course, my prediction was absolutely correct!

This confusing functionality is how Microsoft Project responds when it needs to recalculate the Units value for resources assigned to a task. You see this confusing behavior in two specific situations:

  • You initially assign a resource to a Fixed Duration At a later time, you adjust the Work value for the resource, which means that Microsoft Project must recalculate the Units value for the resource.
  • You initially assign a resource to a Fixed Work At a later time, you adjust the Duration value for the task, which means that Microsoft Project must recalculate the Units value for the resource.

For example, notice in the Task Form view shown in Figure 1 that I assigned Mickey Cobb on a Fixed Duration task with a Units value of 50% and with a Duration value of 10 days. Notice that the software calculated a Work value of 40 hours for her on the task, as expected.

Figure 1: Resource assigned to a Fixed Duration task


Because the task is Fixed Duration, the Duration value is fixed or “locked” so that the value will not change. If I change the Work value to 60 hours, Microsoft Project must recalculate the Units value because it is the only remaining non-fixed variable. However, notice in Figure 2 that the software did not recalculate the Units value as expected! What is going on here? Is this a bug? No, it is not a bug. It is a consequence of the new functionality introduced back in Microsoft Project 2010.

Figure 2: Units value is not recalculated as expected


To implement this new functionality, the software development team for Microsoft Project 2010 created two new assignment fields in the software: the Assignment Units field and the Peak field. Because these two fields are assignment fields, you can only see them in the Task Usage view and the Resource Usage view. Neither of these fields are included in the default layout of these two views, so you must insert these fields manually if you want to see them and use them.

Figure 3 shows the Task Usage view with the Assignment Units and Peak fields inserted in the view. Notice that the Assignment Units field for Mickey Cobb displays the original Units value of 50%. Notice that the Peak field displays the new calculated Units value of 75%. To confirm that Mickey Cobb is correctly scheduled to work at a Units value of 75%, notice that the timephased grid on the right shows that she is assigned to work 6 hour per day for each day of the task schedule.

Figure 3: Assignment Units and Peak fields


I mentioned several times that this new functionality was introduced initially in the 2010 version of Microsoft Project, but you should know that this functionality is present in every other version of the software, including the 2013, 2016, and 2019 versions. When you see this confusing behavior in any of the last four versions of the software, keep in mind that what you are seeing is not a bug. The behavior is by design and cannot be changed, even if the design can be confusing.


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Written by Dale Howard

Dale Howard is currently a Senior PPM Consultant with Arch Systems, Inc. His hair and beard have turned white because of using Microsoft’s project management tools for more than 20 years. Dale started his career using Microsoft Project 4.0 for Windows 95 and began using Microsoft’s PPM tools when they introduced Project Central in 2000. Dale is the co-author of 23 books in Microsoft Project, Project Server, and Project Online. He is currently one 0f 26 Microsoft Project MVPs in the entire world and one of only 4 Project MVPs in the United states.

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  1. Thanks for explanation.

  2. Thanks Dale – have been very aware of this “fix” since the 2010 release and have never understood what “new functionality” was actually added to cause this change. You mention it as well but it’s still not clear…and what bug did they fix that caused this change? I wasn’t aware of the Peak field so thanks again for sharing.

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