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Task duration does not update based on 50% resource utilisation

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  • #415679 Reply
    Ben Smithson


    I create a task (with 1 week duration) and assign a resource to it. However this resource/person can only work 50% of their time on this task. I therefore want the task duration to automatically calculate in MS Project to 2 weeks. How do i acheive this?

    Currently i:
    1. create a task
    2. assign a single resource to it
    3. assign 1 week as ‘task duration’ within Task Information > General tab
    4. within Task Information > Resources tab, change ‘Units’ from 100% to 50%
    5. Click OK

    at this point i would expect MS Project to autoamtically recalculate the task duration from 1 to 2 weeks (based on 1 weeks worth of work and resouce utilised at 50%). Unfortunately the task length and finish date do not adjust and remain at 1 week

    I appreciate this is probably v basic stuff, but i’m stuck! I’m not sure if my process is correct and/or there are other settinngs within Project that need adjusting

    Version: MS Project Proffesional 2016

    Thanks in advance

    #415680 Reply

    When you manually defined the task duration as 1 week, MS project behind the scenes changes the task to Fixed Duration. Meaning, that pretty much the only way the task duration will change will be if you manually alter it.
    The solution is pretty simple. Change the task type to Fixed Units. Once you change the task type, change the Work value from lets say 40, to 39, then back to 40. This change will force Project to recalculate the duration as explained in the additional info below.

    Additional info
    Project has an internal formula “Duration = Work / Availability” where availability is resource assignment units equated to hours of work time available per day. This formula must always be in balance. When you define a task as Fixed Work, you are locking the Work portion of the formula, meaning if you manually change availability, duration is recalculated. It works the same for Fixed Units (availability), meaning the Availability is locked and if you change the amount of work, the Duration will be recalculated.

    Generally speaking, if you are working on projects where duration should be driven by work and resource availability, you will probably want to set your task types to Fixed Units. For example, Bob is available to the project at 60% so by setting the task type to Fixed Units, you’re telling Project not to change Bob’s task assignment units value.

    Hope that helps! 🙂

    #415681 Reply
    Larry Christofaro

    Daryl has done a good job of explaining all the options and settings involved in assigning resources…which can get very complicated to the novice user so good going Daryl. One more thought that might help is to make sure you assign a units value at the time you assign the resource instead of after the fact. If you assign the resource as 50%, then it will assign the correct work without changing the duration with any of the task types. Two common ways to assign resources with the desired units in one step is to use the Assign Resources function or using a split screen with the task form on the bottom. Of course there’s also the assignment of additional resources which is dependent on the Effort Driven flag so be careful of that as well. Hope that helps…

    #415682 Reply
    Ben Smithson

    Thanks Daryl and Andy. That explains everything perfectly

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