Microsoft Project: Are you making this common mistake – Wrong Task Type!

Just realized that I have not covered Microsoft Project at all in my blog so far. So let me start with the commonest mistake. The mistake is – not changing the Task Type. Tasks can be of three types. But most people just use the default one. And that can lead to unnoticed side effects. Learn how to prevent and repair the mistake.
(Reading time 7 min)

Microsoft Project - Wrong task type

Task Types

A project consists of lots of tasks. Add a task and right click to open Information dialog. Under the advanced tab, notice the Task Type dropdown.


By default all tasks are fixed units. However, you can change the type of task to Fixed Duration or Fixed Work. The problem is – when we are adding tasks, we usually keep the default task type.

Ideally, the task type should be considered and changed for individual tasks by thinking about how the actual task will be executed and its nature from a business point of view.

Unfortunately, I have not seen this happen for EVERY tasks. What does that mean? Potentially, some tasks have the wrong task type – leading to an erroneous schedule. Obviously it will have a compounding effect on all aspects of managing that project on a longer term.

Why is this so confusing?

Because of the word FIXED. So let me fix this once and for all. First of all let us understand what a project is all about.

There is work to be done. Lots of work. We need someone to do the work – we call them resources. They work as long as they can – that is called resource units. Typically 8 hours a day we do some job. Now if there is lot of work, we will need more time to do it. That is the duration. If there is WORK which requires 16 hours to do and I am doing it single handedly – I will need to work for 16 resource units. In terms of duration it will be two days because I don’t work for 16 hours at a stretch.

So we have this formula

Time required to get work done = Total work to be done / Ability to work

or more technically – same formula shown in different ways.

Duration = Work / Resource units

Work = Duration * Resource Units

Resource units =  Work /Duration

Now, depending upon business situations, all these parameters can change. But in a given situation, these cannot change in isolation. If one thing changes it affects the other two.

For example, if you increase the duration, work can increase or resources can decrease. What is actually going to happen depends upon the type of task at hand. If you have limited resources then we want Project to understand that it cannot change the resource units. That is indicated by changing the task type to Fixed Units.

So when one parameters changes manually, which of the other two parameters cannot be changed automatically is called FIXED. Of course, the fixed parameter itself can be changed manually. For example, by hiring more people we can increase the available resources. But even in that case, this increase is MANUAL. Project should not add more resources because there is still a limit on their availability. In this case, if you increase the work, project will increase the duration. If you increase the duration, Project will increase the work.

In short, the parameter which PROJECT cannot touch automatically is called Fixed. So the best way to understand the meaning of the word FIXED is – look at it as a business constraint or common sense based rule.


Fixed Units

This is the default. The idea is that resources are limited. So once you assign resources – which obviously has to be done manually, Project will have to work by manipulating either work or duration. If you increase work, duration will increase and vice versa. Why? Because the units are frozen by human beings (called Fixed).

Fixed Work

We know the actual amount of effort involved. For example, based upon estimates, one piece of software requires 10 hours to complete. Now depending upon which other parameter you decide, the third parameter will be calculated.

If you give only 1 tester for one hour per day, the duration will be changed to 10 days. If you want to set the duration to one day, then Project will demand 10 testers (assuming all of them can work for only 1 hour per day).

Fixed Duration

This is best understood based upon common sense. Consider exporting fruits. Once harvested, fruits require fixed amount of time to ripen. Only after they ripen can they be packaged. Adding more resources does not decrease the duration. In this case, we make the task as Fixed Duration.

Effort Driven Check Box

Of course this is another confusing thing. Now that we understand the meaning of FIXED, you will learn this one very quickly.

First of all, Fixed Work type is always Effort Driven. Why? Because if work is constant, adding more resources will finish it faster – so it is obviously effort driven.

The problem arises with Fixed Units and Fixed Duration type of tasks.

If you have limited resources (fixed units), by increasing the work will the duration increase? It should – logically. That is why we enable the Effort Driven check box. Even if you don’t enable it, Project asks you various questions to decipher if it is effort driven and it will do the necessary calculation. But the checkbox does not actually get checked in this case.

Same situation in Fixed Duration type of tasks. Usually because duration is fixed, Adding resources does NOT increase or decrease the work involved. Hence Effort Driven option does not seem to be relevant. But it is.

Suppose one task has a fixed duration of 4 days. You add one resource, it will be allocated for 8 hours per day for four days. Now if you add one more resource, the duration is fixed. So the work will be reduced to half for both of the resources. That is how Effort Driven works.

If Effort Driven is removed, each resource added will be added for full time. For example, if I am conducting  a training program for three days, all attendees must be present full time. That is a Fixed Duration task which is NOT Effort Driven.


Think of the real life task scenario and choose the right Task Type and decide whether it is Effort Driven or not. Do this WHILE you are adding tasks – not after adding all tasks.

If you get confused, try changing the other two parameters (non-fixed ones) and see how the other parameter is affected. If it is as per business needs, you have chosen the right settings. If not, change the settings and try again.

That’s all there is to it.


Comments? Suggestions? Wish list?