Understanding Task Types in Microsoft Project

Remember the formula: Work = Duration × Units

Effort Driven Scheduling:

• On (default for Fixed Work): Total work stays the same – adding resources shortens duration.

• Off: Total work may increase when adding resources.

• Fixed Duration + Effort Driven: Duration stays the same; units drop to absorb work.

A common cause of frustration when assigning resources in Microsoft Project is how the work is scheduled. You may find that after assigning a few resources the duration of the task increases, or maybe it reduces, or just doesn’t behave how you expected. This frustration stems from a lack of understanding of how task types work.

This article looks to demystify how task types affect a schedule as well as provide examples of situations when one task type is more appropriate.

If you’ve ever assigned resources in Microsoft Project or Microsoft Planner Premium and watched your schedule change in unexpected ways, you’ve already seen task types in action.

Perhaps your task duration suddenly stretched, shortened, or didn’t move at all. That’s not a glitch — it’s Project following the rules of the task type you’ve set (or the default it’s using).

In this guide, we’ll explain exactly what a task type is, how the three task types work, when to use each, and how “Effort Driven” scheduling changes things. This applies whether you use Microsoft Project Desktop, Project Online, or Microsoft Planner for the web (formerly Project for the web)

What is a Task Type in Microsoft Project?

A task type tells Microsoft Project which of three factors will stay fixed when you make changes to a task:

• Work – the total effort needed to complete the task, usually in hours

• Duration – the total time span for the task, in working days

• Units – the resource allocation, expressed as a percentage of a resource’s availability

Every task in Project is one of three types: Fixed Units, Fixed Work, or Fixed Duration.
This setting controls how Project recalculates your schedule when you change one of the three factors above.

What is the formula behind task types?

All task types follow the same scheduling formula:

Work = Duration × Units

• If you know any two, Project will calculate the third.

• The “Fixed” in the task type name means that factor won’t change automatically — the other two will adjust instead.

How do the three task types work?

1. Fixed Units – Units (allocation %) stays the same.
Changing duration changes work; changing work changes duration.

2. Fixed Work – Total work (hours) stays the same.
Changing units changes duration; changing duration changes units.

3. Fixed Duration – Task length stays the same.
Changing units changes work; changing work changes units.

Pro tip: If changes don’t seem visible, add the Peak Units column to see actual resource effort.

What does “Effort Driven” mean in Microsoft Project?

Effort Driven scheduling controls what happens when you add or remove resources:

• Effort Driven ON: Total work stays the same. Adding resources shortens the duration (for Fixed Work and Fixed Units tasks).

• Effort Driven OFF: Total work can increase when you add resources.

• Fixed Duration + Effort Driven: Duration stays the same, but resource units drop to fit the same total work.

When should I use each task type?

Use Fixed Units when:

• The number of people or % allocation is your main known factor

• You can’t increase resources (e.g., a fixed team size)

• You want someone assigned at a steady part-time allocation (e.g., 10%)

Use Fixed Work when:

• You estimate in hours of effort

• You know the exact amount of work required

• Effort estimates are more accurate than duration guesses

Use Fixed Duration when:

• Deadlines dictate how long the task can run

• Adding resources won’t shorten the timeframe (e.g., training, compliance)

• The schedule is calendar-driven, not work-driven

How do I change a task type?

In Microsoft Project Desktop / Online:

1. Right-click the task → Information

2. Go to the Advanced tab

3. Select the Task Type

4. Click OK

In Microsoft Planner for the web:

1. Open the task’s detail pane

2. Look for Task Type under scheduling options

3. Select Fixed Units, Fixed Work, or Fixed Duration

Common mistakes with task types

• Not setting the correct task type before assigning resources

• Forgetting that Fixed Work is Effort Driven by default

• Linking summary tasks, which can cause scheduling conflicts — link milestones or subtasks instead

Key takeaways

• Task types define how Project recalculates your plan.

• Always decide your “fixed” factor before making schedule changes.

• Combine task type settings with Effort Driven scheduling for precise control.

Bottom line: Understanding task types puts you in control of Microsoft Project’s scheduling engine. Instead of being surprised by shifting dates, you’ll be able to predict exactly what will happen when you tweak your plan – in Project Desktop, Project Online, or Planner for the web.