Apply Constraints

​​​​ I. Editable: Constraints:

  1. ​As Late As Possible (ALAP)
  2. As Soon As Possible (ASAP)
  3. Start No Earlier Than (SNET)
  4. Finish No Earlier Than (FNET)
  5. Start No Later Than (SNLT)
  6. Finish No Later Than (FNLT)
  7. Must Finish On (MFO)
  8. Must Start On (MSO)

Constraints allow you to control the start or finish date of an automatically-scheduled task. There are three types of constraints:

Flexible constraints 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.

Semi-flexible constraints require an associated date that controls the earliest or latest start or finish date for a task. These constraints allow a task to finish at any time, as long as it meets the start or finish deadline.

Inflexible constraints require an associated date that 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.

Project management tip In nearly all cases, use the ASAP constraint. This gives the scheduling engine the most flexibility in determining the ideal finish date for your project.

Here are two ways to instantly view the constraints on your tasks.

To review or change the constraint on a task, right-click on the task, click Task Information , then click the Advanced tab. Constraint information is in the Constraint type and Constraint date boxes.

If the constraint is anything other than ASAP or ALAP, the constraint type will display its associated graphical indicator in the Indicator column in any sheet view, such as the Gantt chart.

Constraints with moderate scheduling flexibility will restrict a task from starting or finishing before or after a date you choose. For example, a task with a Start No Earlier Than (SNET) constraint for June 15 and a finish-to-start dependency to another task can begin June 15 if its predecessor is finished by June 15 (or later if its predecessor finishes after June 15), but it can't be scheduled before June 15. For example, this might be appropriate use of constraints if you have a building permit that is only good for a specific dates. In this case, the SNET or FNLT constraints might be used.


 

BulletBlue1.gifWith the default finish-to-start task relationship and an ASAP constraint applied to these tasks, the successor task (the second one) is scheduled to begin as soon as the predecessor task (the first one) is scheduled to finish.

BulletBlue2.gifWith a SNET constraint applied, the successor task cannot begin before the constraint date, even if (as shown here) the predecessor task is completed before the constraint date.

The following table lists the constraints provided in Project.

Constraint type Constraint name Description
Flexible As Late As Possible (ALAP)Schedules the task as late as possible with the task ending before the project ends and without delaying subsequent tasks. This is the default constraint for tasks when you schedule from the project finish date. Do not enter a task start or finish date with this constraint.
Flexible As Soon As Possible (ASAP)Schedules the task to begin as early as possible. This is the default constraint for tasks when you schedule from the project start date. Do not enter a start or finish date with this constraint.
Semi-Flexible Start No Earlier Than (SNET)Schedules the task to start on or after a specified date. Use this constraint to ensure that a task does not start before a specified date.
Semi-Flexible Finish No Earlier Than (FNET)Schedules the task to finish on or after a specified date. Use this constraint to ensure that a task does not finish before a certain date.
Semi-Flexible Start No Later Than (SNLT)Schedules the task to start on or before a specified date. Use this constraint to ensure that a task does not start after a specified date.
Semi-Flexible Finish No Later Than (FNLT)Schedules the task to finish on or before a specified date. Use this constraint to ensure that a task does not finish after a certain date.
Inflexible Must Finish On (MFO)Schedules the task to finish on a specified date. Sets the early, scheduled, and late finish dates to the date that you type and anchors the task in the schedule.
Inflexible Must Start On (MSO)Schedules the task to start on a specified date. Sets the early, scheduled, and late start dates to the date that you type and anchors the task in the schedule.

By default, all tasks in a project that is scheduled from the start date have the ASAP constraint applied. Likewise, by default, all tasks in a project that is scheduled from the finish date have the As Late As Possible (ALAP) constraint applied.

Inflexible constraints usually override any task dependencies and restrict a task to a date you choose. For example, a task with a Must Start On (MSO) constraint for September 30 and a finish-to-start dependency to another task will always be scheduled for September 30 no matter whether its predecessor finishes early or late. You can change this behaviour. Click File, click Options, click Schedule, then select the Tasks will always honour their constraint dates check box.​


 

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