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Ask the Teacher: What Determines If a Task is Critical or Not?

Rebecca of Lansbury, PA asks, “I am trying to display a critical path for my plan. When I display the filter for critical, only a few tasks appear. How can I quickly identify the real critical path and free float associated with it?

Answer: Great question! Several factors determine the task critical path, so lets start with viewing the critical path so we can see what’s going on in the schedule. The Gantt View isn’t formatted to see the critical path as a default. Some of the views are preformatted. It’s easy to format a Gantt chart using the Gantt chart wizard. If you have put custom formatting into a Gantt chart and then run the formatting wizard, you run the risk of the previous formatting being overwritten. For that reason, it’s best to run the Gantt chart wizard and then enter any custom formatting you might require. Here’s how to use the Gantt chart wizard to show the critical path.

  1. Click on the Gantt Chart Wizard button (looks like a magic wand) on the formatting toolbar or go to Format | Gantt Chart Wizard.
  2. Click Next.
  3. Click on Critical Path and Finish.

Figure 1. The Gantt Chart Wizard

Ask the Teacher: What Determines If a Task is Critical or Not?

4. Click on Format It and Exit Wizard

The Critical Path appears in red, but there’s more you should be looking at. This critical path calculation is based on the default values that stated that if there’s zero slack, the task is critical. What you’re not seeing is that if there’s one minute of slack, the task is considered non-critical. The question is, do you feel that one minute of slack is a good delineation between critical and non-critical

You have the ability to control this demarcation point — an option found at Tools | Options | Calculation. The last option reads:

“Tasks are critical if slack is less than or equal to: _________ Days.”

This tolerance level is a number of days, and the value should be based on the length and size of your schedule. Two days might be too little for a two-year project but would be more appropriate for a two-month project. Keep in mind that this is a per-project option and should be reset for each project schedule.

The tolerance level is looking at the Total Slack and Free Slack columns in the schedule. By inserting these columns, you’ll be able to see the reason a task is considered critical or not. When you apply the critical filter, the filter is looking at the column “Critical.” This column, as a system default, is being recalculated every time you change anything within the project schedule.

Figure 2. The Total Slack and Free Slack columns exposed

Ask the Teacher: What Determines If a Task is Critical or Not?

The critical path calculation is also being influenced by relationships, constraints, deadlines, resource assignments, and task, resource and project calendars. Only you can determine if the critical path is correct. Double-checking the above factors for correctness is important.

To identify the slack in your schedule easily, you might also view the Detail Gantt. Slack will be represented as teal-colored lines extending to the right of a Gantt bar. In Figure 3 I’ve turned off the Gantt lines for easier viewing.

Figure 3. Viewing the slack

Ask the Teacher: What Determines If a Task is Critical or Not?

Thanks for asking!

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Written by Ellen Lehnert

Ellen Lehnert, PMP, Microsoft Project MVP, MCP, is a independent consultant and trainer on Microsoft Project and Project Server. She has taught Microsoft Project over 400 times and is the author of  MS Project 2010 and

2013 published courseware. Ellen is also a contributor and tech editor for many reference books, a developer for the Microsoft Project certification tests and is a frequent meeting speaker for Microsoft, MPUG and PMI. Contact Ellen at ellen@lehnertcs.com.

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