By default, Microsoft Project calculates tasks as critical if slack is less than or equal to 0 days. In the following illustration, Task A is not critical as it has 1 day of total slack:
To access the option controlling critical, from the File tab select Options, and then click Advanced and scroll to the bottom of the Advanced page as shown in the following illustration:
Suppose you have a project that is proceeding on track, but you want to see not only the tasks that are critical, but the ones that are almost, or nearly, critical. Then simply change the option to 1 days.
Once changed, Task A is considered critical as shown in the following illustration:
Applies To: All Current Versions of Microsoft Project