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When a Fixed Duration Task is Truly Not “Fixed Duration”

Oh, the misery! If you’ve ever used Fixed Duration tasks in your enterprise projects running in Microsoft Project Online or Project Server and your organization uses the Timesheet page in Project Web App (PWA) to track actual task progress, then no doubt you have experienced heartache and disappointment. Those Fixed Duration tasks don’t behave the way they’re supposed to. You know I’m speaking the truth if you’ve ever seen this Microsoft Project warning dialog:

(Memorize this screenshot. You’d be seeing it a lot if you were the project manager in the following scenarios.)

Most project managers assume that using Fixed Duration tasks will guarantee that the Duration and Finish date won’t change for these tasks. Unfortunately, nothing could be further from the truth!

There are multiple scenarios that can cause the Duration and/or the Finish date to change on a Fixed Duration task. These scenarios include (but aren’t limited to) the following:

  • Scenario #1. A team member submits planned nonworking time (such as vacation) for a period between the Start date and Finish date of the task.
  • Scenario #2. A team member enters an initial Actual Work value on a date later than the Start date of the task when the task has multiple resources assigned.
  • Scenario #3. A team member increases the Remaining Work value after completing all the planned work on the task.
  • Scenario #4. A team member doesn’t finish the planned work by the Finish date of the task.
  • Scenario #5. A team member enters an Actual Work value on a date later than the Finish date of the task.
  • Scenario #6. A team member enters task progress earlier than the Start date of a task that has a Finish No Earlier Than (FNET) or Must Finish On (MFO) constraint applied.
  • Scenario #7. The project manager reschedules uncompleted work from the past into the current reporting period.

Scenario #1. Planned Vacation

The next screenshot shows the sample project I use in this article. Notice that Calvin Baker is assigned to Task A. This Fixed Duration task has a Duration of 10 days and a Finish date of June 16.

Calvin submits a week of planned vacation as nonworking time on his Timesheet in PWA for June 12-16. The next time this enterprise project is opened, the project manager will see the warning dialog I showed previously. The next figure shows the Gantt Chart view of the project that reveals the impact of Calvin’s vacation. Notice that the Duration of this Fixed Duration task has changed from 10 days to 15 days, and the Finish date has slipped from June 16 to June 23.

Scenario #2. Actual Start is Later Than the Planned Start

Task B is a Fixed Duration task with a Duration of 10 days and a Finish date of June 16. Using the Timesheet page in PWA, team members submitted their Actual Work for their Task B assignments for the week of June 4, as shown in the next screenshot. Notice that Cindy McNair submitted two hours of Actual Work for each day of the week. Notice also that Jerry King submitted two hours of Actual Work only on Friday, a date that is four days later than the expected Start date of his assignment work on this task.

After approving the task updates, the project manager will get the warning dialog when the enterprise project is opened. Because Jerry started his assignment work four days later than originally scheduled on this Fixed Duration task, Project has changed both the Duration and the Finish date of this task, as shown in the next figure. Notice that the Duration has increased from 10 days to 14 days and the Finish date has slipped from June 16 to June 22.

The next screenshot shows the Task Usage view for Task B, with the last two weeks of planned Work displayed in the time-phased grid. Notice how Jerry’s planned Work slips four days into the week of June 18. This slippage is a result of Jerry starting four days late on his assignment work for this task, which caused the Duration to increase by four days and the Finish date to slip by four days as well.

Scenario #3. Remaining Work Increase

Task C is a Fixed Duration task with a Duration of two days and a Finish date of June 6. On his Task C task assignment, Larry Barnes was originally assigned to work eight hours each day on Monday and Tuesday of the week of June 4. Using the Timesheet page in PWA, Larry Barnes entered eight hours of Actual Work on Monday and Tuesday, which caused the Remaining Work to drop to zero hours. Larry increased the Remaining Work to 16 hours because he still hadn’t completed the task, and then submitted the update to his project manager. You can see his task update for this assignment in the next figure.

After approving the task update from Larry, the project manager opened the enterprise project. Project displayed its warning dialog. The next image shows the Gantt chart view for Task C. Notice that the Duration of this Fixed Duration task has increased from two days to four days, and the Finish date has slipped from June 6 to June 8.

Scenario #4. Actual Work Behind Schedule

Task D is a Fixed Duration task with a Duration of two days and a Finish date of June 6. On her Task D task assignment, Linda Erickson was originally assigned to work eight hours each day on Monday and Tuesday of the week of June 4. Using the Timesheet page in PWA, Linda entered only four hours of Actual Work each day on Monday and Tuesday and then submitted the task update to her project manager. You can see her task update for this assignment in the next figure. Notice that her eight hours of uncompleted Work has been rescheduled to Wednesday of that week.

After approving the task update from Linda, the project manager opened the enterprise project and saw the warning dialog. The next screenshot shows the Gantt Chart view for Task D. Notice that the Duration of this Fixed Duration task has increased from two days to three days, and the Finish date has slipped from June 6 to June 7.

Scenario #5. Actual Work Past the Finish Date

Task E is a Fixed Duration task with a Duration of two days and a Finish date of June 6. On her Task E task assignment, Marcia Bickel was originally assigned to work eight hours each day on Monday and Tuesday of the week of June 4. Using the Timesheet page in PWA, Marcia entered eight hours of Actual Work each day during all five days of the week and then submitted the task update to her project manager. You can see her task update for this assignment here:

After approving the task update from Marcia, the project manager opened the enterprise project and received the warning dialog. The next figure shows the Gantt chart view for Task E. Notice that the Duration of this Fixed Duration task has increased from two days to five days, and the Finish date has slipped from June 6 to June 9.

Scenario #6. Early Progress on a Constrained Task

Task F is a Fixed Duration task with a Duration of 10 days, a Start date of June 12 and a Finish date of June 23. This task has a Finish No Earlier Than (FNET) constraint applied with a constraint date of Friday, June 23, which means that the task can’t finish earlier than that date.

On her Task F task assignment, Mickey Cobb was originally scheduled to start work on Monday, June 12. Because of an early finish on a task in another project, Mickey Cobb could start early on her Task F assignment on Friday, June 9. Using the Timesheet page in PWA, Mickey Cobb entered eight hours of Actual Work on Friday, June 9 and submitted the task update to her project manager. You can see her task update for this assignment here:

After approving the task update from Mickey, the project manager opened the enterprise project. In this situation, however, Project hasn’t displayed the warning dialog we’ve come to know so well. The next screenshot shows the Gantt Chart view for the Task F task. Even though the software doesn’t show the warning dialog, notice the Duration of this Fixed Duration task has increased from 10 days to 11 days and the Start date of the task has changed from June 12 to June 9.

Scenario #7. Reschedule Uncompleted Work

Task G has a Duration of 10 days and a Finish date of June 16. Susan Tartaglia and Terry Uland were each originally scheduled to work 40 hours on this task during the week of June 4. However, they could complete work only on Monday and Tuesday before they were pulled off this project to help with a higher priority project. Using the Timesheet page in PWA, Susan and Terry each entered eight hours of Actual Work on Monday and Tuesday, June 5-6, and then submitted their task updates to their project manager. You can see the task updates for their assignments in the next image.

After approving the task updates from Susan and Terry, the project manager opened the enterprise project. The following screenshot shows the Gantt Chart view of the project with the task updates applied on Task G. By the way, the red dotted line in the Gantt Chart pane is the Status Date line.

Because Task G now has three days of uncompleted work in the past (work scheduled to the left of the Status Date line), the project manager rescheduled the uncompleted work into the next week using the Update Project dialog. Once again, Project won’t display the warning dialog. The next figure shows the Gantt Chart view for the Task G task after rescheduling uncompleted work from the past. Notice that the Duration of this Fixed Duration task has increased from 10 days to 13 days, and the Finish date has slipped from June 16 to June 21.

A Final Recommendation

I have now documented at least seven situations that can cause the Duration to increase and the Finish date to slip for Fixed Duration tasks. If your organization is using the Timesheet page to capture task progress in the Microsoft PPM solution, Project Online or Project Server, then I advise against using Fixed Duration tasks in your enterprise projects. To eliminate the confusion and the frustration caused by Fixed Duration task behavior, my recommendation is that you use either Fixed Work or Fixed Units tasks instead.

Dale Howard
Written by Dale Howard

Dale Howard is the Director of Education for Sensei Project Solutions.  He is in his 15th year of serving as a Microsoft Project MVP (Most Valuable Professional) and is currently one of only 39 Microsoft Project MVPs in the entire world. Dale is the co-author of 21 books on Microsoft Project, Project Server, and Project Online. He works out of his home in Ellisville, Missouri (a west suburb of St. Louis).

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6 Comments
  1. Thank you for another outstanding article that brings clarity to a topic that is often not fully grasped by some who have been scheduling for years. I will be looking over your books to see how they could benefit my practice and that of my colleagues.

    Reply
  2. Hello Dale,

    Thanks for an excellent article and I would add that Fixed Work may be more appropriate for companies who are using time sheets for managing contractors or controlling costs, simply because planned work shouldn’t increase if the duration expands. Just depends.

    Reply
  3. Thank you for this wonderful article that was so well explained with clear examples. I will surely want to look at your book to gain a better understanding of how to handle these changing situations that happen all the time with shifting priorities.

    Reply
  4. Thank you for the clarification and clear way of explaining the different scenario’s.
    For some reasons you could address this as “bug” or unexpected side-effects, but I don’t understand why Project Server does not provide the possibility for “real” fixed duration tasks.
    Within our organisation we have a mix of project-based work and maintenance: the tasks for maintenance work are planned for a fixed duration and fixed amount of hours per week. When a resource enters real maintenance hours (varies per week), duration and planned hours/week for the remaining period will be changed. This gives a wrong number of hours available for project-based work and needs manual repair every week…
    Are we the only organisation with this kind of mixed work and need for proper resource planning? Sounds familiar?

    Reply
  5. Dale once again make the complex as simple as possible. Another good writer on the complexities of using resources is Eric Uyttewaal. Between Eric and Dale, they pretty much cover it all in their books. Hope you guys never retire!

    Reply
  6. Can anyone explain why changing the task type to Fixed Duration changes the Duration (and % Complete with it)

    e.g. A task with multiple resources on Fixed Units or Fixed Work has Duration 31.68d. Changing to Fixed Duration increases Duration to 34.87d (the effect is repeatable switching back and forth between the different types)

    Effort driven does not affect this, work is not moved around and nothing else appears to change.

    Reply

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