Types of Constraints

Eight types of constraints are available in Microsoft Project. By default, all tasks are assigned the As Soon As Possible constraint. You can, however, choose the constraint that best meets a task’s start or finish requirements.

As Soon As Possible is the most commonly used constraint.

Most constraints are based on a date you specify, tying the start or finish of a task to that date. With As Soon As Possible and As Late As Possible constraints, Microsoft Project can schedule tasks flexibly relative to the predecessor and successor tasks.

The following table lists the eight types of constraints, describes each type, and states when each type should be used.

Constraint	Description	Use for
As Soon As Possible (ASAP)	Starts the task as soon as possible based on links to other tasks. Allows schedule changes to start tasks earlier or later.	Starting a task as soon as its links with predecessor tasks, if any, allow. Do not enter a date with this constraint.
As Late As Possible (ALAP)	Starts the task as late as possible based on links to other tasks. Allows schedule changes to start tasks earlier or later.	Starting a task as late as possible without delaying the project end date or the finish date of a successor task. Do not enter a date with this constraint.
Finish No Earlier Than (FNET)	Finishes the task on or after the date you enter. Allows schedule changes to finish tasks later.	Tasks that perhaps can but shouldn’t finish before a specific date, such as the aging process for cheese. Microsoft Project automatically assigns this constraint when you enter a task finish date.
Start No Earlier Than (SNET)	Starts the task on or after the date you enter. Allows schedule changes to start tasks later.	Tasks that must start on or after a specific date. Microsoft Project automatically assigns this constraint when you enter a task start date.
Finish No Later Than (FNLT)	Finishes the task on or before the date you enter. Allows schedule changes to move the finish date up to, but not beyond, the specified finish date.	Tasks that must finish by a specific date.
Start No Later Than (SNLT)	Starts the task on or before the date you enter. Allows schedule changes to move the start date up to, but not later than, the specified start date.	Tasks that must start by a specific date.
Must Finish On (MFO)	Finishes the task on a specific date. Schedule changes don’t affect the finish date.	Tasks that must finish on a specific date.
Must Start On (MSO)	Starts the task on a specific date. Schedule changes don’t affect the start date.	Tasks that must start on a specific date.