Using Microsoft Project Fixed Duration, Fixed Work and Fixed Unit Type Fields

Microsoft Project Tutorial: Learn how to use fixed duration, fixed work and fixed unit fields

A lot of users have questions on MS-Project fixed work vs fixed duration fields.  This lesson focuses on the project planning phase and using the different task types to build an accurate work breakdown structure. After the project manager and other stakeholders understand the project scope, the project can be decomposed into manageable chunks and individual tasks with time estimates.

Estimates are predictions of task effort and duration. MS-Project supports different task types including Fixed Duration, Fixed Work and Fixed Unit types. It is important to understand these project types and how they interact with MS-Project. Creating a project plan with a mix of fixed work and fixed duration tasks is recommended. The MS-Project Type field allows the project manager to create a well-defined project plan with status meetings and reviews built into the project schedule. The plan becomes a more accurate representation of project execution.

A typical project includes tasks that are effort driven and duration driven. A project manager may include duration task types such as milestone reviews after each lifecycle phase. Since these milestones are dependent upon the work in each phase, it is helpful to include them in the plan to organize and communicate project status. These meetings are added to the project plan with a Fixed Duration task type. Any team status meeting, project milestone review or code review meeting is a fixed duration task. A one-hour team status meeting has a one-hour fixed duration regardless of the number of resources attending the meeting. The amount of work will fluctuate depending on the number of attendees.

Writing a project charter document, coding a software program or building a detailed project plan are fixed work tasks. The Fixed Work task type is useful when team members provide estimates by task. A task to develop a report is estimated at 40 hours with one team member assigned. The amount of work is fixed at 40 hours and the duration changes depending on the team members’ availability. If the team member is available 100 percent of the workweek, the report should be completed in five days.

The Microsoft Project Formula

MS-Project uses the following formula to calculate duration, resources (units) and effort.

Duration X Units = Work

MS-Project expects the user to provide two of the inputs and MS-Project calculates the third. To view these fields and the impact of Task Types, additional fields need to be added to the Task Entry View.

To create a Fixed Duration task:

  1. Insert the Type field into the Gantt Chart view
  2. Enter the task name
  3. Change the Type field to Fixed Duration
  4. Enter the Duration
  5. Enter the Resources
  6. Effort will be calculated by MS-Project

To create a Fixed Work task:

  1. Insert the Type field into the Gantt Chart view
  2. Enter the task name
  3. Change the Type field to Fixed Work
  4. Enter the Effort in the Work field
  5. Enter the Resources
  6. Duration will be calculated by MS-Project

A helpful reminder in the Duration X Units = Work is to pick two of the variables (duration, units, or work) and let Microsoft Project calculate the result.  Remembering this tip will help you avoid the resource overallocation frustration as the variables change as you enter a resource allocation of 100% and then try to adjust both duration and work.  Experiment with these task types to understand the relationship duration, units and work share in MS-Project. Including these task types in the plan will develop a more realistic plan that reflects actual execution and gain better control over key dates and milestones.

About Andrew Makar

Professional Cat Herder and an Agile Enthusiast with a keen interest in putting PM theory into actual practice.

16 Responses to Using Microsoft Project Fixed Duration, Fixed Work and Fixed Unit Type Fields

  1. Matthew Busse July 9, 2013 at 9:05 pm #

    Thank you! Finally an explanation of the difference between Fixed Duration and Fixed Work that makes sense!

  2. Neale Partington March 25, 2015 at 4:39 pm #

    Struggling with Project 2010 – I would like to be able to enter work and duration and have Project assign the units accordingly. Instead, when I do that, it leaves the units at 100% unless I adjust them manually. So if I have an activity that takes 8 hours to complete over 8 days, and enter both, it recalculates to 64 hours of work instead of 8. My solution has been to either not plan work, or to enter work in a number field for each of my resources or resource categories. From looking at other MSFT articles, it appears that 2010 is the first time this happened? I don’t recall.

    • Andrew Makar March 25, 2015 at 7:55 pm #

      Hi Neale –

      Try to change your task types to Fixed Duration, assign 8 hours to Work and 8 days to the duration.
      Then assign the resource. You should get a .13 allocation on the resource.

      I saw the same issue when I assigned a Fixed Units resource after assigning Work = 8 hours and Duration = 8d. Fixed Duration will solve it for you as you’re saying the total duration of the task is 8d and you’re assigning 8 hours of work. When you assign the resource it calculates a .13 unit allocation. If you change the resource allocation, MS Project will indeed increase the work to 64 hours.

      fixeed duration example

      I pick the task type (Fixed Duration), enter the task type value (8d), provide either a work or resource value and let MS Project calculate the rest. Unless you’re doing effort based scheduling, my preference is for fixed duration tasks. It keeps life a little simpler and you can still manage to your dates.


      • Debbie March 31, 2015 at 3:23 pm #

        I am having the exact same issue. I want units to calculate and I cannot get MS Project to do this for me. Even if I set the task as fixed duration and add the work. This is new/unusual for me. I have been using MS Project for over 15 years. Any other thoughts or approach?

        • Andrew Makar April 2, 2015 at 8:59 pm #

          Hi Debbie – Are you assigning 1 resource to the task or multiple resources?

          I’ll write a longer tutorial shortly. Let me know what you’re seeing and what your steps are and I can see if I can recreate the issue.

          In my experience, I have seen MS Project fail to calculate properly if there is a lot of changes to a task with work, duration and resources already assigned.
          If you select a task type (Fixed Duration), assign the duration and the work, then the resource unit % will adjust accordingly.

          • Rakhi October 14, 2015 at 4:46 am #

            Hi Andrew,

            I am facing the problem in resource loading. I am assigning multiple resources to a particular task. Can you please share the blog which u have mentioned in the earlier reply.


          • Andrew Makar December 19, 2016 at 2:24 am #

            My advice on this one is to always break down the tasks into single level tasks so only 1 resource is assigned.

      • Douglas Brown July 4, 2015 at 5:33 pm #

        Your default task type is probably set to “fixed-units”, a bizarre choice that is how MSP-2010 comes out of the box. Rather than fixing it in every task as you go along (or not, as you forget to do it), you might consider going into the File/Options/Scheduling dialog and changing that default to fixed-work (the theoretically-correct approach) or fixed-duration which seems to match many people’s real experience.

        MSP will still default the resource to whatever its maximum is in the resource sheet when you first assign it.

  3. Diane Ellison April 22, 2015 at 7:38 pm #

    Dont forget to set “effort-driven” correctly, even for fixed duration. If you want to hold the duration to 8 days, and the work to 8 hours, “effort-driven” needs to be set ON. The purpose of the “effort-driven” attribute is to hold WORK value on a task constant. Effort-driven calculations (provide you with units) but ONLY take effect when you add resources to or remove resources from a task, AND the calculations apply ONLY AFTER the first resources are initially assigned. Meaning, if you initially add two resources you get different UNITS than if you initially add only one resource then subsequently add another resource. Try it with a test schedule! and, here is a good article to clarify how the engine works:

  4. Shaya January 8, 2016 at 11:19 am #

    Hey Andrew,
    very nice article !!! i love ur explanations and bookmarked it. when are you going to post the longer tutorial you promised with multiple resources??? pls do it ASAP. Thanks for you sharing .

  5. Steffen February 12, 2016 at 2:05 pm #

    Thanks, all nice and clear. Only Thing that’s still mind-boggling – how does the “effort driven” Checkbox come into Play? Or, in other words, can anbody explain the difference between a “fixed work” Task and a “fixed Units” Task with the “effort driven” Checkbox turned on? Somehow Looks identical to me, so why do I Need the “effort driven” Parameter at all?

  6. Brian Allen August 4, 2016 at 5:16 pm #

    What is the best way to update fixed duration tasks? Do you use the percent complete or do you enter the actual start and finish dates?

    • Andrew Makar December 19, 2016 at 2:20 am #

      My preference is to use actual start and finish dates as that will adjust the dates accordingly.

      • Brian Allen January 25, 2017 at 2:23 am #

        Thank you for such a quick response! Does this mean you don’t use the update project function? Do you use percent complete at all? I have experienced some errors when I attempt to increase the duration of a task that has some work completed on it. Have you ever experience anything like this?

        Is it common to use project for duration only and not include costs and resource loading into your schedule?

  7. joey January 12, 2018 at 1:27 pm #

    I have a similar problem. I have fixed duration and Fixed effort (work) and want to calculate the average number of resources. I have entered the start and stop dates and the work hours. When I add a resource, the program defaults to 1 resource and change the work.

    • Andrew Makar February 19, 2018 at 6:36 pm #

      If you’ve chosen the task to by Fixed Duration, then I would assign the Duration and if you have to pick a start date (Constraint based task), do so and then assign the work and then the resource name.
      Use a Fixed Duration Task with 5 days of duration and 48 hours of work. When you enter a resources name (Joe), the resource will be allocated 120% or Joe[1.2].
      The resource is overallocated so you will have to adjust the duration or the work. You can also access the Resource Usage view and allocate the hours with more accuracy.

      With this formula, you can pick 1 variable to hold constant (Fixed Work 5 day task), enter another variable (Work) and then the 3rd is ALWAYS calculated.
      Any adjustment to these values will cause a change in the calculation.

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