Quick Links

Avoiding Resource Overallocation

In my experience, one of the more complex and multifaceted subjects in Microsoft Project is assigning resources to tasks. This is one of the lengthiest subjects we address in our training classes and it tends to bring about many questions from students.

When talking with seasoned Project users, the one thing that they always tend to struggle with is resource leveling within their schedule. However, the other day I had a brain wave that avoids confusion: ‘set the task up the task first’

Before you consider building a project team and assigning resources, you need to specify the ‘Duration’ AND the ‘Work’ for each task. A question students and other Microsoft Project users tend to ask me is: “Aren’t ‘duration’ and ‘work’ the same thing?” The answer is NO, they are not the same thing – they are actually not related to one another. The ‘Work’ for a task is the number of ‘man hours’ needed to complete a task. The ‘Duration is the time it takes to complete the task. Let me explain:

Below I have tasks a, b, c and d each with an estimated duration of 3 days.

Resource Overallocation 1

After inserting the ‘Work’ column you will notice that even though I have estimated 3 day duration for each task, there is no ‘Work’ in the ‘Work’ Column. In fact there will never be any ‘work’ for the tasks until you assign a resource, or will there??

Resource Overallocation 2

As I have already mentioned, ‘Work’ and ‘Duration’ is not the same thing. The current schedule states that tasks (a, b, c and d) will take 3 days to be completed. However, that doesn’t tell us how much work we need to do within this time period to complete the task in terms of ‘man hours’.

With the ‘Work’ column added to the table, we can manually specify how many ‘Work’ hours are needed to compete the task within the ‘Duration’ allocated.

Resource Overallocation 3

We have now specified not only the ‘Duration’ but the ‘Work’, this is crucial. When I now assign a resource or resources to this task we will see that the resources ‘Units’ are calculated for us, allowing the user to work on other tasks at the same time if he is not working exclusively (100% units) on this one task.

When I assign Dave Peterson to task ‘a’ we see that the units for this task are calculated at 100%; this is because Dave works 8 hours per day, In this scenario 3 days of full time work equates to 24 hours.

Resource Overallocation 4

When I assign Harry Ramsdon to task ‘b’, (which I have estimated to be 6 days duration and 48 hours’ work) Harry is able to perform all of the 48 hours’ work within the 6 days which means Harry is allocated 100% units.

Resource Overallocation 5

When I assign a second resource to task ‘b’ we can see that the duration is cut in half; this is because the task is an effort driven task. When originally planning this task I had anticipated Harry Ramsdon working full time, doing all of the 48 hours’ work within the 6 days duration. However, it became possible to assign a second ‘helper’ resource to the task. When I do this the duration is cut to 3 days as each resource takes an equal share of the work (24 hours).

Resource Overallocation 6

When estimating task ‘c’ I estimated that the task would take 3 days to complete but within that 3 days there would only be 8 hours of ‘Work’ to be completed. When I assign Mike Fisher to this task you can see that his units are calculated to be 33%, this is HUGE. Mike Fisher is now available to work on other tasks for 66% of his typical working day.

Resource Overallocation 7

I have estimated for task ‘d’ a duration of 3 days but only 6 hours of ‘Work’ to be completed within that time. When I assign Tom Henry to this task we can see his Units are calculated to be 25% making him available to other tasks on the project for 75% of his typical working day.

Resource Overallocation 8

I have found that the easiest way to avoid errors is to estimate both ‘Duration’ and ‘work’ prior to even looking at possible resource assignments. Try to get a good understanding of how many man hours (work) are involved in each task and then estimate the duration of the task. The default ‘Gantt Chart’ view in Microsoft Project displays the ‘Duration’ Column but does not expose the ‘Work’ Column. Therefore, Project Managers will estimate the rarely enter ‘Work’ estimates in addition to the ‘Duration’ for given tasks, this is one of the main causes of resource overallocations.


Follow Tom Henry on twitter @tomhenryepm 

Avatar photo
Written by Tom Henry

Tom Henry is the PPM Practice Manager at Projility, where he leads a team of experienced project and portfolio management consultants in making clients more adept, productive and profitable. Tom has been involved with PPM since graduating from Bournemouth University in the United Kingdom, working first in London and then moving to the United States to further pursue his career. Tom prides himself on being able to understand his clients’ needs and translating those needs into simplified PPM solutions. Contact Tom at tom.henry@projility.com.

Share This Post
  1. Great article. I though it may be helpful to add some information about Task Type too.
    – When you assign a second resource to task ‘b’ the duration is cut in half because [Effort Driven] = “Yes” AND [Task Type] = “Fixed Work” or “Fixed Units”.
    – If [Effort Driven] = “Yes” but [Task Type] = “Fixed Duration”, Work and Duration don’t change when you add the second resource.

    Type Effort Driven When second resource is assigned
    Fixed Units Yes Duration cuts in half, Work stays the same
    Fixed Work Yes Duration cuts in half, Work stays the same
    Fixed Duration Yes Duration and Work stay the same
    Fixed Units No Duration stays the same, Work doubles
    Fixed Duration No Duration stays the same, Work doubles
    Note: When [Type] = “Fixed Work” the [Effort Driven] field can’t be set to “No”

  2. Thank you Tom for your explanation.
    As Jill Baird said, it’s also very important to analyze the task type. In may experience after inputting duration and work efforts, I check if task type is correct. A common mistake is when you have a meeting and you set this task as ‘fixed work’. A meeting is normally a ‘fixed duration’ task no matter how many participants you have.

    Best regards,

  3. Hi Tom
    Good point about the work column. I find it less practical that it is hidden and that project does not set work = duration automatically without a resource assigned.
    I came across a situation when project stops calculating units for soms tasks and sets 80% units for all the tasks. This happens when you publish the project for the first Time and the local resources het converted to enterprise. Any idea why it happens?

Leave a Reply