Critical path in MS Project

What the critical path is

The critical path is the chain of linked tasks that sets the earliest date the project can finish. A delay to any task on it delays the finish, because those tasks have no float to absorb it (or negative float, when the finish is held to a date the logic cannot meet). Other tasks can slip a little without moving the finish date.

How MS Project finds it

MS Project marks a task as critical when its total slack (its float) is at or below a limit, 0 days by default. The limit is under File > Options > Advanced: "Tasks are critical if slack is less than or equal to". A completed task is never critical. On the same page, "Calculate multiple critical paths" gives each separate chain of linked tasks its own late dates and critical path, as if it were a small project of its own; the overall critical path still sets the project finish (Microsoft: Critical fields).

How to show the critical path in MS Project

• In the Gantt Chart view, open the Format tab and tick Critical Tasks: the bars of critical tasks turn red.
• The Detail Gantt and Network Diagram views show critical tasks in red as well (Microsoft: show the critical path).
• To list only the critical tasks, apply the Critical filter (View > Filter).

Without MS Project

Ask for the schedule as an .xml file: in MS Project, File > Save As, then choose XML Format (*.xml) as the file type. Open it on this page to see the critical tasks in start order with their dates and float, plus the whole schedule and a DCMA 14-point health check. A binary .mpp file cannot be read here.

How this page reads your file

• It shows the tasks the file marks as critical: MS Project's Critical field, or P6's longest-path flag in an .xer file, as last calculated in that software. The page does not recalculate the schedule.
• When the file has no critical marking at all (an older P6 export without the longest-path column), it lists the tasks with total float of zero or less instead, and says so. When the file marks none as critical, the page says that and only notes how many have float of zero or less.
• Completed tasks, summary rows, level-of-effort and inactive tasks are left out of the critical path list.