About constraints

Constraints (constraint: A restriction set on the start or finish date of a task. You can specify that a task must start on or finish no later than a particular date. Constraints can be flexible [not tied to a specific date] or inflexible [tied to a specific date].) impose restrictions on the way Microsoft Office Project 2003 calculates the start (start date: The date when a task is scheduled to begin. This date is based on the duration, calendars, and constraints of predecessor and successor tasks. A task's start date is also based on its own calendars and constraints.) and finish dates (finish date: The date that a task is scheduled to be completed. This date is based on the task's start date, duration, calendars, predecessor dates, task dependencies, and constraints.) of tasks. By default, Project applies flexible constraints (flexible constraint: A constraint that is flexible and does not tie a task to a single date. Flexible constraints are As Soon As Possible, As Late As Possible, Finish No Earlier Than, Finish No Later Than, Start No Earlier Than, and Start No Later Than.), such as As Soon As Possible (ASAP), to tasks.

For optimal scheduling flexibility, it's recommended that you allow Project to use flexible constraints to calculate the start and finish dates for tasks based on the durations (duration: The total span of active working time that is required to complete a task. This is generally the amount of working time from the start to finish of a task, as defined by the project and resource calendar.) and task dependencies (task dependencies: A relationship between two linked tasks; linked by a dependency between their finish and start dates. There are four kinds of task dependencies: Finish-to-start [FS], Start-to-start [SS], Finish-to-finish [FF], and Start-to-finish [SF].) you enter. Only if you have unavoidable constraints, such as an event date that cannot be moved, should you consider setting a constraint for a task manually.

ShowFlexible constraints

Flexible constraints (flexible constraint: A constraint that is flexible and does not tie a task to a single date. Flexible constraints are As Soon As Possible, As Late As Possible, Finish No Earlier Than, Finish No Later Than, Start No Earlier Than, and Start No Later Than.) such as As Soon As Possible (ASAP) and As Late As Possible (ALAP) do not have specific dates associated with them. Setting these constraints allows you to start tasks as early as possible or as late as possible with the task ending before the project finish, given other constraints and task dependencies in the schedule.

ShowInflexible constraints

Inflexible constraints (inflexible constraint: A constraint that is inflexible because it ties a task to a date. The inflexible constraints are Must Finish On and Must Start On.) such as Must Start On (MSO) and Must Finish On (MFO) require an associated date, which controls the start or finish date of the task. These constraints are useful when you need to make your schedule take into account external factors, such as the availability of equipment or resources, deadlines, contract milestones, and start and finish dates.

ShowSetting of constraints

When you enter a new task in the Task Name field, Project assigns the As Soon As Possible (ASAP) constraint when you schedule your project from the start date. When scheduling from the finish date, Project assigns the As Late As Possible (ALAP) constraint.

If you drag the mouse in the chart portion of the Gantt Chart to create a new task, however, Project automatically assigns the Start No Earlier Than (SNET) constraint when you schedule your project from the start date. When scheduling from the finish date, Project automatically assigns the Start No Later Than (SNLT) constraint.

When you manually enter a start or finish date for task, you automatically apply a constraint to it.

When you schedule your project from the start date and you type a start or finish date for a task, Project constrains the task to begin or complete no earlier than that date. If you schedule your project from the finish date, however, Project constrains the task to begin or complete no later than the date you type.

ShowConstraints and task dependencies

Constraining a task that is dependent on another task can produce unwanted results, as illustrated in the following example:

The task "Pour foundation" is linked so that it starts as soon as "Dig hole" finishes; "Dig hole" is supposed to happen on the 10th. If you enter an inflexible constraint that forces "Pour foundation" to start on the 10th and then "Dig hole" finishes early, Project will not be able to take advantage of the early finish and move "Pour foundation" to start earlier.

Rather than setting specific dates for a task, consider assigning an As Soon As Possible (ASAP) constraint and enter a deadline (deadline: A target date indicating when you want a task to be completed. If the deadline date passes and the task is not completed, Project displays an indicator.) for the task. Entering a deadline causes Project to display a deadline marker on the Gantt Chart, and an indicator (indicators: Small icons representing information for a task or resource that are displayed in the Indicators field. The Indicators field is located to the right of the ID field and appears in a number of tables.) will alert you when the task's finish date moves past the deadline.

 
 
Applies to:
Project 2003