There is more than one type of Task in Microsoft Project

Many people that use Microsoft Project call themselves Project Managers… how can they be Project Managers if they don’t know how to use Microsoft Project properly?

What many Project Managers do not actually realise is that there are three distinctly different types of tasks within Microsoft Project, each have unique behaviours, and more often than not, the default type of task is not appropriate. In addition, there is another attribute, Effort Driven, that can have a huge impact on the schedule produced by Microsoft Project. (Microsoft Project does not produce a project plan)

The three types of tasks used in Microsoft Project are:

  1. Fixed Units
  2. Fixed Work
  3. Fixed Duration

Fixed Unit Tasks

Fixed Unit Tasks are the default in Project 2010 when using the auto schedule option and are

not affected by the effort supplied by the allocated resources, unless the task is marked as Effort Driven.

By default, using automatic scheduling, Project creates Fixed Unit tasks that are not affected by effort supplied by resources. That is, any changes you make do not affect the amount of any resource assigned to a task.

This task type ensures that resource allocations remain constant on the task. So, if you assign two resources — one at 100% and one at 50% — to a task and you remove the resource you assigned at only 50%, Project will not change the other resource’s allocation to compensate.

Source: Project 2010 Bible

Example: If you double the resources allocated to the task, the task dates will not change automatically. You can however override this behaviour by setting the effort driven option in Projects 2010’s default settings.

Fixed Work Tasks

I find this to be the most appropriate type of task to use when scheduling work that involves people because the amount of work is directly affected by the number of resources allocated to the task. This task is natively Effort Driven, which cannot be changed.

Almost every task is affected by the effort supplied by resources. Here’s a simple example: Suppose you have to plant a tree. One person needs two hours to plant a tree. If you add another person (another resource), then it’s reasonable to assume that together they need only one hour to complete the task. That is, two resources, each putting in an hour of effort, complete the two hours of work in only one hour. With resource-driven scheduling, when you add resources, the task duration becomes shorter; if you take away resources, the task takes longer to complete. And, on the flip side, the resource assignments to a task don’t change when the work increases or decreases.

Source: Project 2010 Bible

Example: If you allocate 4 people to an 32 hour (4 day) task, Microsoft Project will allocate each of the 4 resources for 8 hours with a total duration of 1 day.

Fixed Duration Tasks

The number of resources allocated to a fixed duration task do not have affect on the final duration of the task.

You also can use the Fixed Duration task type in Project. The number of resources does not affect the timing of this type of task. To allow a week for a committee to review the company’s new ad campaign — no matter how many people are on the committee — give the task a fixed duration.

You can’t shorten the task’s duration by adding resources to it. In fact, adding people to the review process may lengthen the task, because their effort has no impact on getting the work done more quickly, and coordinating their efforts can add time.

Source: Project 2010 Bible

Example: A flight from Melbourne to Perth will take approximately 4 hours, no matter how many pilots or crew are on board the aircraft.

Effort Driven Tasks

Almost every task is affected by the effort supplied by resources. Here’s a simple example: Suppose you have to plant a tree. One person needs two hours to plant a tree. If you add another person (another resource), then it’s reasonable to assume that together they need only one hour to complete the task. That is, two resources, each putting in an hour of effort, complete the two hours of work in only one hour. With resource-driven scheduling, when you add resources, the task duration becomes shorter; if you take away resources, the task takes longer to complete. And, on the flip side, the resource assignments to a task don’t change when the work increases or decreases.

Source: Project 2010 Bible

Effort-Driven Scheduling and Task Types

Below is a summary of the types of tasks and how the Effort Driven attribute affects the schedule.

Type of Task When Effort Driven When Not Effort Driven
Fixed Work If you add resources, Project shortens the task’s duration Not applicable, because all Fixed Work tasks are effort-driven
Fixed Unit If you add resources, Project shortens the task’s duration Adding resources doesn’t affect the task’s units or duration, but Project increases the task’s total work
Fixed Duration Because the task’s duration is fixed, adding resources doesn’t affect the task’s duration, but Project reduces the allocation of each resource The task’s duration and all resource allocations remain the same when you add resources, but Project increases total work

Source: Project 2010 Bible

One thought on “There is more than one type of Task in Microsoft Project

  1. I have an issue adding new tasks where MS Project on autoschedule extends the task by reducing the % allocation of the resource.

    e.g. A task of 1 day by one person will take two weeks to finish.

    Any ideas why?

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