Tasks don't schedule as expected in Microsoft Project

Summary

This article describes why a task may not be scheduled as expected in Microsoft Project and offers suggestions for correcting the behavior.

More Information

Project 2010

A task may not schedule as expected for a number of reasons. To determine the exact cause in Project 2010, review the following questions:

Note

Before testing any of the scenarios in this article, make a backup copy of the file or save any changes you might have made to the file.

  1. Is the Calculate project after each edit option set to off?

    When you specify a manual calculation, Microsoft Project will calculate your file only when you press F9. Set Calculation to On to resolve scheduling conflicts.

    To set the calculation method, follow these steps:

    a. On the File tab, select Options.

    b. Select the Schedule tab.

    c. Under Calculation, select either On or Off.

  2. Is the Show Scheduling Messages option turned off?

    If the Show Scheduling Messages option is turned off, changes to the project file that result in scheduling conflicts will be processed. If the Show Scheduling Messages option is turned on, you will be able see the conflict and correct it.

    To turn the Show Scheduling Messages option on or off, follow these steps:

    1. On the File tab, select Options.
    2. Select the Schedule tab.
    3. Uncheck the Show Scheduling Messages check box.
    4. Select the Advanced tab.
    5. Under Planning Wizard, select all check boxes.

    Note

    After scheduling messages are turned on, press F9 on the keyboard. Any scheduling messages that occur must be resolved before the project will be calculated correctly.

  3. Are you scheduling from the project's Start Date or the project's Finish Date?

    When scheduling from the project's Start Date, the task will begin as soon as possible.

    When scheduling from the project's Finish Date, the tasks will begin as late as possible.

    To check which date is set in your file, select Project Information on the Project tab.

  4. What is the project's Start Date?

    If the Show Scheduling Messages option is turned on, and you enter a task that occurs before the project's Start Date, you will receive a warning message. If you want to schedule a task to start before the project's Start Date, manually enter the date for the task. To check the Project Start Date, select Project Information on the Project tab.

  5. Did you enter a percent complete on a task?

    If you entered a percent complete on a task, and the task has already started, you cannot change the Start Date automatically. To determine where the task would schedule automatically, set the task to zero percent complete. To do this, follow these steps:

    1. Select the task.
    2. On the Task tab, select Task Information.
    3. Select the General tab.
    4. In the Percent Complete box, type 0.
    5. Select OK.
  6. Did you assign an Actual Start Date to the task?

    You can assign an Actual Start Date to a task and not enter a percent complete. The task will not be scheduled automatically unless you set the Actual Start Date to NA.

    To set the Actual Start Date, insert the Actual Start Field into your table. To do this, follow these steps:

    1. Select the title of any column currently in your table.
    2. On the Format tab, select Insert Column.
    3. Select Actual Start for the Field Name and select OK.
  7. Did you assign a constraint type other than As Soon As Possible (ASAP) to the task?

    A constraint can cause a task to be scheduled according to the type of constraint and the date set. In Microsoft Project, a task that has the constraint of As Late As Possible (ALAP) in a project is scheduled from the project's Finish Date.

    To check the constraint type, follow these steps:

    1. Double-click the ID number for the task.
    2. Select the Advanced tab.
  8. Are there any predecessor or successor relationships?

    The type of relationship will determine when the task can be scheduled. In Microsoft Project, the Task will always honor their constraint dates setting overrides the task relationship links.

    To set this option, follow these steps:

    1. On the File tab, select Options.
    2. Select the Schedule tab.
    3. Select the check box Tasks will always honor their contraint dates.
    4. Select OK.
  9. Are you using automatic Resource Leveling?

    Automatic resource leveling will add delay to a task to avoid resource conflicts. This results in the task Start Date being pushed out. If you select the manual option, delay will not be added to tasks automatically.

    To remove any delay added to a task and to set resource leveling to manual, do the following:

    • To remove delay, select Clear Leveling on the Resource tab.

    • To set resource leveling to manual, select Leveling Options on the Resource tab, and then select Manual.

  10. Is there a value in the Task Delay field?

    If the Task Delay field contains a value greater than zero, you cannot schedule the task earlier. To clear the Delay field, see step 9.

  11. Is the task a subtask?

    If a Summary task (at any level) has a predecessor or a constraint, the subtask cannot be scheduled any earlier than the summary task.

    To check a summary task for predecessors or constraints, follow these steps:

    1. Select the task.
    2. On the Task tab, select Task Information.
  12. Is there a resource assigned to the task?

    The resource calendar can affect the scheduling of a resource-driven task but not a fixed duration task. In Microsoft Project, the resource calendar can affect all three task types (fixed duration, fixed work, and fixed units). Remove the resource to see if, in fact , the resource is affecting the scheduling. After the resource is removed, if the task schedules as expected, then check the resource's calendar.

    To check the Resource calendar, on the Project tab, select Change Working Time, and then select the resource name from the drop-down list.

  13. Are you trying to schedule a task during a non-working time?

    If a day is marked as non-working, then you cannot schedule a task to start on that day. To check the Project Calendar, select Change Working Time on the Project tab.

  14. Are there any predecessor or successor relationships assigned to summary tasks?

    Predecessor and Successor relationships assigned to summary task can affect sub task of the summary task in addition to the summary task(s) that are linked.

    The type of relationship will determine when the task can be scheduled. In Microsoft Project, the Tasks will always honor their constraint dates setting overrides the task relationship links. Earlier versions of Microsoft Project do not have this option.

    To set this option, follow these steps:

    1. On the File tab, select Options.
    2. Select the Schedule tab.
    3. Select the check box Task will always honor their constraint dates.
    4. Select OK.

Project 2007

To determine the exact cause in Project 2007 and earlier versions, review the following questions:

Note

Before testing any of the scenarios in this article, make a backup copy of the file or save any changes you might have made to the file.

  1. Is the Calculation option set to Manual?

    When you specify a manual calculation, Microsoft Project will calculate your file only when you press F9. Set Calculation to Automatic to resolve scheduling conflicts.

    To set the calculation method, follow these steps:

    1. On the Tools menu, select Options.
    2. Select the Calculation tab.
    3. Under Calculation, select either Automatic or Manual.
  2. Is the Show Scheduling Messages option turned off?

    If the Show Scheduling Messages option is turned off, changes to the project file that result in scheduling conflicts will be processed. If the Show Scheduling Messages option is turned on, you can see the conflict and correct it.

    To turn the Show Scheduling Messages option on or off, follow these steps:

    1. On the Tools menu, select Options.
    2. Select the Schedule tab.
    3. Select to select or clear the Show Scheduling Messages check box.
    4. Select the General tab.
    5. Under Planning Wizard, select all check boxes.

    Note

    After scheduling messages are turned on, press F9 on the keyboard. Any scheduling messages that occur must be resolved before the project will be calculated correctly.

  3. Are you scheduling from the project's Start Date or the project's Finish Date?

    When scheduling from the project's Start Date, the tasks will begin as soon as possible. When scheduling from the project's Finish Date, the tasks will begin as late as possible. To check which date is set in your file, select Project Information on the Project menu.

  4. What is the project's Start Date?

    If the Show Scheduling Messages option is turned on, and you enter a task that occurs before the project's Start Date, you will receive a warning message. If you want to schedule a task to start before the project's Start Date, manually enter the date for the task. To check the Project Start Date, select Project Information on the Project menu.

  5. Did you enter a percent complete on a task?

    If you entered a percent complete on a task, and the task has already started, you cannot change the Start Date automatically. To determine where the task would schedule automatically, set the task to zero percent complete. To do this, follow these steps:

    1. Select the task.
    2. On the Project menu, select Task Information.
    3. Select the General tab.
    4. In the Percent Complete box, type 0.
    5. Select OK.
  6. Did you assign an Actual Start Date to the task?

    You can assign an Actual Start Date to a task and not enter a percent complete. The task will not be scheduled automatically unless you set the Actual Start Date to NA. To set the Actual Start Date, insert the actual start field into your table. To do this, follow these steps:

    1. Select the title of any column currently in your table.
    2. On the Insert menu, select Insert Column.
    3. Select Actual Start for the Field Name and select OK.
  7. Did you assign a constraint type other than As Soon As Possible (ASAP) to the task?

    A constraint can cause a task to be scheduled according to the type of constraint and the date set. In Microsoft Project , a task that has the constraint of As Late As Possible (ALAP) will be scheduled as an ASAP task in a project that is scheduled from the project's Finish Date.

    To check the constraint type, follow these steps:

    1. Double-click the ID number for the task.
    2. Select the Advanced tab.
  8. Are there any predecessor or successor relationships?

    The type of relationship will determine when the task can be scheduled. In Microsoft Project , the Tasks will always honor their constraint dates setting overrides the task relationship links.

    To set this option, follow these steps:

    1. On the Tools menu, select Options.
    2. Select the Schedule tab.
    3. Select to select the check box Tasks will always honor their constraint dates.
    4. Select OK.
  9. Are you using automatic Resource Leveling?

    Automatic resource leveling will add delay to a task to avoid resource conflicts. This results in the task Start Date being pushed out. If you select the Manual option, delay will not be added to tasks automatically. To remove any delay added to a task and to set resource leveling to manual, do the following:

    • To remove delay, select Clear Leveling.
    • To set resource leveling to manual, select Resource Leveling on the Tools menu, and then select Manual.
  10. Is there a value in the Task Delay field?

    If the Task Delay field contains a value greater than zero, you can not schedule the task earlier. To clear the Delay field, see step 9.

  11. Is the task a subtask?

    If a Summary Task (at any level) has a predecessor or a constraint, the subtask cannot be scheduled any earlier than the summary task. To check a summary task for predecessors or constraints, follow these steps:

    1. Select the task.
    2. On the Project menu, select Task Information.
  12. Is there a resource assigned to the task?

    The resource calendar can affect the scheduling of a resource-driven task but not a fixed duration task. In Microsoft Project , the resource calendar can affect all three task types (fixed duration, fixed work, and fixed units). Remove the resource to see if, in fact the resource is effecting the scheduling. After the resource is removed, if the task schedules as expected, then check the resource's calendar. To check the resource calendar, follow these steps:

    On the Tools menu, select Change Working Time, and then select the resource name from the drop down list.

  13. Are you trying to schedule a task during a non-working time?

    If a day is marked as non-working, then you cannot schedule a task to start on that day. To check the Project Calendar, select Change Working Time on the Tools menu.

  14. Are there any predecessor or successor relationships assigned to summary tasks?

    Predecessor and Successor relationships assigned to summary tasks can effect sub tasks of the summary task in addition to the summary task(s) that are linked.

    The type of relationship will determine when the task can be scheduled. In Microsoft Project , the Tasks will always honor their constraint dates setting overrides the task relationship links. Earlier versions of Microsoft Project do not have this option. To set this option, follow these steps:

    1. On the Tools menu, select Options.
    2. Select the Scheduling tab.
    3. Select to select the Tasks will always honor their constraint dates check box.
    4. Select OK.

If you have performed all these tests and you still have a scheduling issue, try to create a new task, or try to delete the problem task, and then re-create it.