PRJ: Incorrect Critical Path Calculation Using Delay

Microsoft Project does not take Delay values into account when calculating the Late Finish for a given task. This can result in incorrect critical path calculations when Delay is used.

Microsoft has confirmed this to be a problem in the versions of Microsoft Project listed above.

Adding Delay to a task is a convenient way to alter the start of a task without actually having to place a constraint on it. For any given task, the following formula holds true: The Late Finish of a task (task x) is calculated from the Late Start (assuming a FS relationship) of its successor task (task x+1): This is the formula used in standard project management methods of calculating critical path, and it is also used by Microsoft Project. These standard methods, however, are based solely on task durations and predecessor-successor relationships; they do not incorporate the concepts of "constraints" or "delay." To take Delay into account, the formula for Late Finish should be: Formula (1) results in a Late Finish for task x that is greater than it ought to be when task x+1 has a Delay > 0. This may produce a Total Slack > 0 for task x, incorrectly making it a noncritical task.