Microsoft KB Archive/88322

= PRJ: Incorrect Critical Path Calculation Using Delay =

Article ID: 88322

Article Last Modified on 11/25/2003

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APPLIES TO


 * Microsoft Project 1.0 Standard Edition
 * Microsoft Project 3.0 Standard Edition
 * Microsoft Project 4.0 Standard Edition
 * Microsoft Project 1.1 for Macintosh
 * Microsoft Project 3.0 for Macintosh
 * Microsoft Project 4.0 for Macintosh
 * Microsoft Project 4.1 Standard Edition

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This article was previously published under Q88322



SYMPTOMS
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.



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



MORE INFORMATION
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:

Scheduled Start = Early Start + Delay

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):

(1) Late Finish(task x) = Late Start(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 &quot;constraints&quot; or &quot;delay.&quot; To take Delay into account, the formula for Late Finish should be:

(2) Late Finish(task x) = Late Start(task x+1) - Delay(task x+1)

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.

Additional query words: slack critical path

Keywords: kbbug kbpending kbusage KB88322

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