Let's assume that

  • the standard number of hours worked per day is 8h
  • I have a task with a Duration of 2 days and 16 Work hours
  • The resource RA is assigned 100% to this task.
  • this task mode is set to Fixed Duration

Now, if I log 24 hours in the Actual Work field, rather then having the usage of the resource RA increasing to 150%, I get the following error message:

The resource is assigned outside the original dates for the task XXXX.

The duration of this fixed-duration task will change to accommodate the resource assignment.


  • How is your Calendar defined for this project?
    – John K. N.
    Feb 14, 2017 at 14:45

2 Answers 2


I am not seeing this in either Project 2016 or Project 2010. When I apply the tracking table and enter 24 hours of actual work on a Fixed Duration task, the message does not appear. Please check to see that your version of Project 2013 is up to date with the most recent public updates. See: https://blogs.technet.microsoft.com/projectsupport/p/msp13/


I set up a basic project with three tasks where each task is configured to be one of the basic task types:

  • Fixed Duration
  • Fixed Work
  • Fixed Units

I then copied the tasks down and grouped then into two groups: Base Plan + Modified Plan.

Base Setup

Base Setup of Standard Tasks (click on image to zoom)

As you can see, there is a task of each specific type and each task has a duration of 2 days and a work amount of 16 hours. I then assigned a resource RA to each task.

Modifying Fixed Duration Task

Modifying a task of type Fixed Duration (click on image to zoom)

After modifying the Fixed Duration task to 24 hours only the Work column was highlighted. No error messages, just a little green triangle telling us that Project has altered something.

Modifying Fixed Work Task

Modifying a task of type Fixed Work
(click on image to zoom)

After modifying the Fixed Work task Project highlighted the duration and end date and provided the little green arrow to hint that I could alter the default behaviour of how Project handled the change.

Modifying Fixed Units Task

Modifying a task of type Fixed Units
(click on image to zoom)

After modifying the Fixed Units task by adding 6 hours to the work Project highlighted the duration and work columns. And again Project lets me know with the little green arrow that I could alter the default modifications to something else, by clicking on the cell and then selecting the exclamation mark symbol to the left of the cell.

Automatic Planning Mode

All these changes were conducted in automatic planning mode, so Project will adjust according to its defaults.

Resource Impact

Impact on Resource Allocation (click on image to zoom)

Adjusting the Fixed Work and Fixed Units tasks resulted in a longer duration of work (3 days), which is the default handling when adjusting the work amount. However, adjusting the Fixed Duration task resulted in a (default) adjustment of the units (resource allocation). The employee RA now has to work 150% on two days of the week to accomplish the **Fixed Duration* task.

Base Formula

The default adjustments are all based on the following formula:

1 day duration = 8 hours per day / 100% Units per day

If we apply this formula to the Fixed Duration task this will result in:

2 d duration = 8 h work per day / 100% units per day => 16 h work / 100% units

We add 8 hours to the work which results in 24 hours in two days, because duration can not be changed:

2 d duration = 8 h work per day / 100% units per day => 24 h work / 150% units

Because the value on the left side of the equation cannot be altered Project has to modify the only value on the right side of the equation that can be altered and that is the value for units (which is the equivalent of resources).

16h / 100% = 0.16h / 1% unit

Which is the same as:

24h / 150% = 0.16h/1% unit

To answer your question

Your error message is not the default behaviour when modifying a Fixed Duration task in MS Project. Project will increase the resource percentage if the task is configured as a Fixed Duration task.

The task type might have been set as Fixed Work or Fixed Units type.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.