Critical Path in MS Project : Best Practices with Free MPP Download

The critical path of a work plan is made up of tasks that together determine the overall duration of a project. Each task that is a part of the critical path has zero slack, and this means that a delay of X days in any one of these tasks will result in a delay of X days in the entire project. These tasks are called critical tasks, and deserve special attention due to their impact on the entire projects’ duration.

Critical Path in MS Project
Critical Path in MS Project

Best Practices 

Using the “Total Slack” column in MSP, it is easy to see which tasks have available slack. These tasks should be delayed first if possible, and thus not delay the entire project.
The “Total Slack” column should also be used when determining if any resources can be re-routed to a critical task.

The projects’ buffer should be calculated as X% of the critical paths’ duration. The percentage should change according to the following criterion – 
  • Complexity of the project: the more complex and innovative the project, the higher the percentage should be.
  • Overall duration: the longer the project, the more than can (and usually will) go wrong. Hence the percentage should rise with the duration.
  • Number of people involved: the more people that are involved, the higher the percentage should be.

The agreed upon buffer needs to be tracked & managed, and ideally the percentage of it that is used should be equal or less than the percentage complete of the entire project.

Negative slack is also possible, if a deadline was used in the project. If a deadline is set to 05-May for example, and the end date is 08-May, the slack for the task that is late by 3 days will show -3 (minus three) in the slack column.

How to create Critical Path in MS Project

Luckily for us, MSP automatically calculates the slack of each task, and if asked will also color the critical tasks red in the Gantt chart. Simply go to the “Format” ribbon, and check the “Critical Tasks” checkbox.

Critical Path Options
Critical Path Options
MSP will also determine the critical path, as long as the user doesn’t use any constraints. A constraint is a hard date that is set as a start / finish date for a task. The constraint is effectively a break in the path, and is set when the user chooses a date in the “Start” or “Finish” columns. Due to this, It is recommended to use only predecessors and duration to set the start / finish dates, and not to choose a date in these columns. 

There are 2 ways to see if there are any constraints in the MPP file – 
  1. Add the “Indicators” column to the plan: If there is an icon of a calendar in a row, then that row has a constraint. Hovering over the icon will show which constraint was used. 
  2. Choose any row. In the “Task” ribbon click on the “Information” button. Go to the “Advanced” tab. If in the “Constraint Type” drop-down menu anything besides “As Soon As Possible” appears, then there is a constraint on the row. Also a date will appear in the “Constraint Date” field. To open the “Information” menu, it is also possible to double-click on the row.
Once no constraints exist in the work plan, MSP will automatically determine the entire critical path.  

Critical Path MS Project
Critical Path MS Project
MSP will also display the available slack for the tasks that aren’t on the critical path. In order to use this feature, go to the “Format” ribbon, and check the “Slack” checkbox. Then in the Gantt chart, you will see black line from the end of the non-critical tasks to the end of their slack.

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