The Top 10 Microsoft Project Scheduling mistakes

Avoid these TOP 10 Microsoft Project mistakes!
Microsoft Project is a powerful piece of software, but that power and complexity makes it very easy to create errors in your plan or reduce the accuracy of your planning.
Microsoft Project is designed to carry out complex calculations that Project Managers used to have to do by hand. The idea is that you input:
  • what you need to do,
  • in what order you need to do it and
  • how long it will take.
Microsoft Project will then calculate start and end dates for each task and the critical path for the project.

The problem is that Microsoft Project hides the complex calculations are going on in the background and often as Project Managers we start using planning software before we know what terms like Critical Path and Float really mean.

This can lead to a number of common scheduling errors and issues in Microsoft Project schedules.

Warning signs that a project plan might not be realistic

This is checklist of issues that I frequently see on Microsoft Project schedules that can be clear sign that the project plan is not detailed enough or not likely to be achievable or that the Project Manager doesn't have a thorough understanding of Microsoft Project.
  1. Broken Critical Path
  2. Lots of Constraints
  3. Project headed straight down
  4. Abandoned Tasks
  5. Overloaded resources
  6. No Parallel Working
  7. No resources or generic role descriptions
  8. Forgetting Holidays
  9. Linking summary tasks
  10. Not getting the plan signed-off

1. Not linking tasks - Broken Critical Path

The Critical Path is the series of tasks that must finish on time for the entire project to finish on schedule. Each task on the critical path is a critical task.
A broken critical path is the first sign that there could be a planning problem. In the example below it is not clear how the tasks relate to one another because not all of the task links are in place.

For example Installation of the software is not linked to Training, but installation is essential for the training to start. Read more on Critical Path Analysis.

A microsoft project schedule with a broken Critical Path
To check the Critical Path use the Gantt Wizard to highlight the critical tasks. If you can’t see an unbroken path running from the first to the last task then there is a missing dependency somewhere. Watch a video showing how to view the Critical Path in Microsoft Project.

2. Lots of constraints

In Microsoft Project constraints can be used to create a link between a task and a particular date.
In the example below a series of ‘Start No Earlier’ constraints have been set against each task. This symbol indicates a constraint has been set.
Microsoft Project plan with lots of constraints
The problem here is that the tasks won’t respond to improvements in the schedule.

For example ‘Local UAT’ is dependent on ‘UAT prep’ which has a planned duration of 3 days. If 3 days was reduced to 2 days then local UAT could start earlier. However, because of the ‘Start No Earlier’ constraint, Local UAT will remain scheduled to start on 18/03 and the improvement won’t impact the plan.

Read more on Microsoft Project Constraints.

3. Project headed straight down

Below we have a lot of similar tasks scheduled to happen at the same time. What I call project headed straight down. This could indicate a high risk approach to delivery, implemented to meet timescales that are not realistic.
Microsoft Project schedule - warning sign project headed straight down
The Project Manager needs to be sure that these simultaneous tasks can be managed and delivered safely i.e. within acceptable levels of risk. Many of the tasks require the same resource type – IT are scheduled to check workstations in two locations on the same day.

The Project Manager needs to be sure there is enough resource to rollout out in several different locations at once.

4. Abandoned Tasks

The cause of a broken critical path, abandoned tasks are tasks that either don’t have a predecessor or successor or both.

Tasks with no predecessors

Microsoft Project Tasks with no predecessors
In the image above Review Local Business Requirements has no predecessors. If a task has no predecessors then in theory there is nothing in the logic of the plan to prevent it happening right now. If you have tasks without predecessors check the plan logic by asking:

    What is preventing this task happening today?

If there are activities that need to happen before this task can start add them to your plan. If you don’t add the tasks then you can’t manage them.

In this example, Review local requirements is probably dependent on a working group who will facilitate sessions to gather the requirements. If the working group activities aren’t included in the planning the project manager has no visibility and can’t control when the working groups deliver, and if they deliver. This also means that the project manager can’t identify and then manage the risks associated with the working group not delivering.

If you don’t have visibility of a task and its dependencies then you can only rely on luck that it will be delivered on time if at all.

Tasks with no successors

tasks with no successors - scheduling error in ms project
In the example below Fix & retest has no successors. This seems odd as surely Cutover (go live) is dependent on the fixes.

If you have tasks without successors check the plan logic by asking:

    Could we finish this project if this task wasn’t completed?

In all likelihood the answer will be no and may trigger the addition of more tasks to ensure all activities are included to get to the definition of Finished. If you find the task task has no impact on the project end date then ask why it is on the project plan?

early in the planning process the plan may have tasks with no successors or predecessors particularly if the work breakdown is being built out in Microsoft Project.
However, a plan that is used to communicate a forecast go live should be questioned if it has tasks with missing successors or predecessors.

5. Overloaded resources

Overloaded resources in microsoft project
Overloaded resources are a common issue on project plan. resources show as over-allocated when they are scheduled for more than the working time available.

Early in the planning sequence overloaded resources will appear particularly if named resources haven’t yet been confirmed. When plans are signed-off and a project has started and overallocated resources suggest an unrealistic plan and should be investigated.

To check if resources are overloaded look for a red person icon in the Indicator column. You can then use the Resource Usage view to understand why a resource is over-allocated.
To access the Resource Usage view click the resource tab then select Resource Usage.

6. No parallel working

Every project manager has been asked the painfully obvious “have you thought of running tasks in parallel?”.
While this can be an irritating question it is worth checking the logic of the schedule to ensure all parallel working has been considered. I have seen project plans with tasks that run in a sequence from start to finish.

This can be caused by the project manager missing the second step in planning sequence - Task precedence or product flow. In other words the project manager may not have answered the question ‘in what order do the tasks need to happen?’

Artificially extending the plan by not considering the true order in which tasks needs to happen is often an unintended consequence of linking summary tasks and a reason by you should avoid this practice.
Of course parallel working is only sensible when it doesn’t causes overloaded resources.
To overlap activities for parallel working the project manager may decide to use start to start, finish to finish or start finish task dependencies. These dependency types can cause delays to not be reflected correctly and should be used sparingly see start to start and finish to finish relationships.

7. No resources or generic role descriptions

When a plan is approved it should be clear which resources are completing each task, the exceptions being summary & milestone tasks. If a task is not allocated to any resources it likely won’t get done.
planning mistake no resources
Equally a generic role description is may not be enough to identify the individual who should be working on the task.

8. Forgetting holidays

The sinking feeling that comes with realising a resource is booked to work over Christmas is not pleasant. Project plans must always take into account working times and non-working times. Microsoft Project makes it possible to create calendars for individuals and for the whole project.

A global .msp file listing all UK public holidays is available here. This can be downloaded and applied to your project plans as a default set of non-working days for UK projects.

9. linking summary tasks

The PMI Practice Standard for Scheduling advises against linking summary tasks because it makes the schedule logic difficult follow, may product logic errors and may create circular logic within the schedule (PMI, 2011, pg. 38).

In Microsoft Project linking summary tasks can be tempting particularly on project plans with a 100s of tasks however there are risks with this approach and generally it is advisable to avoid linking summary tasks.

10. not getting the plan signed off

This applies to all plans not just those created in MS project, but it is included here because without sign-off the project plan is not realistic or achievable – a plan won’t be achieved if the people who can ensure the work happens have not signed off on the tasks or delivery dates.

PMI recommend that the project team should be actively involved in reviewing the results of scheduling. There will likely be multiple reviews to analyze the project end date, milestone completion dates, critical paths, total float values and resource requirements (PMI, 2011, pg. 32)

Top 10 Microsoft Project mistakes - recommended reading

Practice Standard for Scheduling – Second Edition, 2011, Project Management Institute, Pennsylvania. Latest edition of the Practice Standard for Scheduling - Third Edition, 2019.

Read more guides on using Microsoft Project