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MS Project Troubleshooting: Why a Successor Task's Start Date May Not Directly Follow a Predecessor Task's Finish Date

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There could be several reasons why a successor task’s start date is different from its predecessor's finish date:

  1. Calculation is set to manual.
    • For Project 2007 and earlier go to: Tools/Options/Calculation tab and set calculation mode to “automatic”.
    • For Project 2010 and later, go to: File/Options/Schedule group and set calculation to “on”. Or, press F9 to recalculate.
  2.  The start date of the successor task is fixed by a strong constraint such as “Must Start On”, “Must Finish On”, or “Finish No Later Than”. The default option is that in a scheduling conflict situation, Project considers these constraints as more compelling than the link and thus will not move the start date of the successor.
    • For Project 2007 and earlier, this setting can be changed in Tools/Options/Schedule tab: "Tasks will always honor their constraint dates".
    • For Project 2010 and later the option is under File/Options/Schedule group.
  3. The start date of the successor is fixed by its actual start date. This happens if the successor has any progress (i.e. % Complete > 0).
  4. The task is manually scheduled (Project 2010, Project 2013).
    • To keep the task manually scheduled but recalculate the successor's schedule, select the task and click Respect Links on the Task ribbon.
    • To switch the task to auto scheduled, click the Auto Schedule button on the Task ribbon.
  5. The start date of the successor is later than the predecessor's finish date. This can happen due to several reasons:
    • The successor has a “Start No Earlier Than” or a “Finish No Earlier Than” constraint.
    • Another task is linked to the successor and it is driving the successor start date.
    • The successor is a subtask of a summary task which is forced to start later by a constraint or a link (this is one good reason not to link to summary tasks).

To better understand this, remember that Finish To Start links only tell Project that the successor can not start before the finish of the predecessor and they do not imply an "equal to" relationship. Similarly, in case of a Start To Start link, the start of the predecessor will not always match the start of the predecessor; the same reasons apply.

Source reference:

This is a revision of the Project MVP FAQ 50: http://project.mvps.org/faqs.htm#Successors_Start_Date_Is_Different_From_Its_Predecessors_Finish_Date_