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Friday, March 31, 2023

How Does MS Project Works? 6 Task Controlling Factors

Table of Contents for MS Project Working-

  1. Introduction
  2. How Does MS Project Work?
  3. Task Mode
  4. Task Dependencies
  5. Calendar
  6. Task Type
  7. Effort Driven & Non-Effort Driven Tasks
  8. Task Constraints
  9. Conclusion


The Microsoft Project was the first project management software that I learned and put to use. The easy-to-use interface and the powerful scheduling make it an ideal choice for beginners. I have utilised the various views offered by the software to analyse and interpret the data. The Gantt Chart view is the default mode. I also used the network diagram, task usage view, resource usage view etc. for my better understanding of the subject matter.

The use of project management software requires you to be aware of the project management terms. If you are a beginner at MS Project or Project Management, it is highly recommended to go through my other articles (listed below) on MS Project terminologies, else you can continue the article.

Top 20 MS Project Terms Every PM Should Know Part-1

Top 20 MS Project Terms Every PM Should Know Part-2

Assuming you are well-versed with the basic terms of project management, let us now continue to our topic i.e., How Does MS Project Works?

How Does MS Project Works?

There is no doubt that to efficiently use software the best thing is to understand how it works. This is what I did in my initial days of entering into the project management.

I soon figured out that the activities defined in the project schedule in MSP are governed by the task dependencies, calendars, task constraints. These regulators control the scheduling and do the calculations for work allocation, resource levelling, rescheduling on updating the project etc.

The understanding of working with these schedule regulators enabled me to use them to my benefit. I got my answers to questions like “How does this activity is rescheduled?” or “How does resource levelling work?”

The factors that rule the scheduling ability are inter-connected with each other in a complex manner. Initially, I was overwhelmed with it. But with the regular learning and working on it made me more confident in using the functions. The change in any of them may result in an effect on others. However, the impact of the same may be alike for different conditions.

The walk through the complete article will enable you to understand the process of scheduling in MS Project.

The top six factors that govern the scheduling ability of the software are listed below with their detailed descriptions and respective implications.

1. Task Mode

The MS Project uses two types of task modes- manually scheduled and auto-scheduled.

1.1 Manually Scheduled Task-

If a task is set to be manually scheduled, it does not itself calculates the start date and finish date. The manually scheduled task is represented by a cyan coloured pin in the task mode column.

The duration for a manual schedule task can be a number or text. The MS Project ignores the project and resource calendar for such task type.

Advantage- Themanually scheduled task is helpful for the activities that don’t have a specifically defined duration. It also gives us more command over the scheduling.

Task Mode in MS Project
Task Mode in MS Project

1.2 Auto-Scheduled Task-

An auto-scheduled task itself calculates the start date and the finish date. The dates are calculated on the basis of task dependencies, lead &lag, calendar, constraints etc.

Advantage- The auto-scheduled task is helpful as it saves time in feeding the data and reduces the possibility of human error.

2. Task Dependencies

Project schedule activities are interlinked with each other in a sequential manner. The interlink between the activities is called task dependencies. The task dependencies are of four types-

2.1 Finish to Start (FS)-

The start of an activity is linked with the finish of its’ preceding activity. This dependency is widely used in the project schedule and shows the natural flow of work from one activity to another. DCMA guideline for schedule quality check recommends that more than 95% of activities should be linked with the FS relationship.

2.2 Start to Start (SS)-

The start of an activity is linked with the start of another activity. This relationship is used for the activities that can be done in parallel to each other.

2.3 Finish to Finish (FF)-

The finish of an activity is linked to the finish of another. The main problem with this link is that it doesn’t specify the start of an activity. This leads to the obstruction of the natural growth of the logic.

2.4 Start to Finish (SF)-

The finish of an activity is linked to the start of its’ preceding activity. This dependency should be avoided as it reverses the workflow.

How does task dependencies affect the schedule?

The task dependencies create the workflow sequence. Hence, create the critical path as well. The correct links yield the accurate critical path that can be used to control the project effectively.

3. Calendar

The MS Project calendar can be defined for each task. The working hours and days are defined by the user in a custom calendar or the standard calendars provided in the software. The project-specific holidays can also be marked in the calendar.

Want to know more about changing working time and days in MS Project. Click here for the detailed article on it.

Default Calendar in MS Project
Default Calendars

How does calendar affect the schedule?

The project calendar and the resource calendar only allot the work & resource to working hours and days. This way the resource is only allocated to working hours and days. Thus, the resource planning is optimised and the cost is controlled.

4. Task Type

The MS Project offers three types of tasks to choose from- fixed unit, fixed work and fixed duration. These task types are only available for auto-scheduled tasks.

To understand the task type, it is important to understand the meaning of unit, work & duration in the MS Project context. The unit represents the number of resources allocated to execute a task. The work is the quantity of the task. It is represented in the form of work-hours or work-days. The duration is the time taken by the resource(s) to execute the work. It depends upon the resources available to do the work.

Task Type in MS Project
Selecting Task Type in MS Project

4.1 Fixed Unit Task-

The fixed unit task recalculates the duration for change in units or work. For the change in duration, the work is recalculated. This task type is helpful for tasks that have resource constraint.

For example, for manually digging a 1m x 1m x 1m pit only 3 workers can be utilised due to space constraint for doing the task. If the number of such pits is increased to two, the duration will be doubled as the resource unit will remain the same as before.

For the change in duration, the work will be recalculated. For the change in units, the duration will be recalculated keeping the work the same.

4.2 Fixed Work Task-

The fixed work task is used where the quantity of work remains intact on change in duration or unit. For example, the concrete pouring into a foundation is a fixed work task. As the quantity of concrete for the foundation is constant, only the duration can be changed if the resources are changed.

However, if the concrete quantity is changed for whatsoever reason the duration to pour concrete will be changed keeping the units the same.

4.3 Fixed Duration Task-

The fixed duration task is used for the activity that takes a certain amount of time to be completed and can’t be changed. This task type is helpful in meeting the deadline by recalculating the unit or work.

For example, the curing period of concrete is a fixed-duration task. If the units are changed the work is changed but the duration still remains the same. If the concrete area that is to be cured is increased i.e., work, the units are recalculated and the duration remains the same.

For change is duration, the work is recalculated keeping the units intact.

How does task type affect the schedule?

 The three elements i.e., unit, work and duration define the scheduling ability of the software for an activity. The MS Project divides each task into work hours based on the duration and allots the unit per day. Thus, choosing the correct task type will enable the MS Project to reschedule the activity based on the real-world scenario i.e., resource constraint, deadline or the fixed work.

5. Effort Driven & Non-Effort Driven Task

Effort driven task is to control the task duration with the unit. The duration of such a task changes based on the units assigned to it. The name suggests, the task is effort driven means putting more effort into the task will shorten the duration. It only works for auto-scheduled tasks only.

The effort driven scheduling only works after the first resource unit has been assigned to the task. It deals with the changes in the resource unit only.

The fixed work task is always effort-driven as the work always remains the same only duration and the units change. The duration decreases for an increase in the unit.

If fixed unit task is made effort-driven, the duration will decrease on increasing the resources.

For, effort-driven fixed duration task, the increase in resource will decrease the productivity of each unit.

6. Task Constraints

The task constraints control the start date, finish date and duration of a task. The task constraints can be broadly grouped into three types- flexible, semi-flexible and hard.

It is recommended to avoid semi-flexible and hard constraints as they don’t respect the dependencies. It also affects the critical path and may show a false picture of it.

6.1 Flexible Constraint-

The task with flexibles constraints is not provided with start date and finish date. The MS Project itself calculates it.

6.1.1 As Soon As Possible (ASAP)-

The task is scheduled to start as soon as it can occur. This is the default setting for project scheduling from the start date. The ASAP start date is the earliest start time for a task.

6.1.2 As Late As Possible (ALAP)-

The default for project scheduling from the finish date. It schedules the finish date of a task as late as possible without affecting the successor task.

6.2 Semi-Flexible Constraint-

The task with semi-flexible constraint is set to start or finish in respect to a specific date.

6.2.1 Start No Earlier Than (SNET)-

The task set to start no earlier than a specified date. This may be used for a task that has a certain requirement that can only be fulfilled after a certain date. For example, the concrete mixer machine breaks down and the maintenance will be completed on x date. The concreting task may be set to start no earlier than x date.

6.2.2 Finish No Earlier Than (FNET)-

The task set to finish no later than a specified date.

6.2.3 Start No Later Than (SNLT)-

The deadline is set to start date of a task. For example, the promoter is visiting the site on x day and you want to make sure the concreting works for certain structure to start before his/her visit.

6.2.4 Finish No Later Than (FNLT)-

This constraint limits the finish date of a task.

6.3 Hard Constraints-

6.3.1 Must Start On (MSO)-

This constraint fixes the start date for a task on a certain day.

6.3.2 Must Finish On (MFO)-

The finish date is fixed to a certain day and the MS Project schedules the task to meet the deadline.


The MS Project uses a number of factors to decide the project finish date and resource assignment. However, the above mentioned six factors are sufficient to broadly understand the working. The factors such as float, resource assignment, resource levelling etc. also affect the scheduling ability of the software.

The factors that affect the scheduling ability of MS Project majorly depends upon the requirement of the project manager. The greater the complexity of the schedule, the greater is the number of factors ruling it.

The understanding of the working method of the MS Project will definitely empower you to create a better schedule. It will also help you to modify or update the schedule as per the different real-world scenarios.

I hope you have got the answer to the big question- How does MS Project works?

Liked the article? Or Have I missed anything? Let me know in the comments below.

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