Constraints

A constraint is a requirement that is set for a task's start or finish date. A constraint affects how a task's start and finish dates will be affected by other tasks in a task plan, based on the relationships between the tasks and the schedule for the task plan itself. There are two types of constraints: flexible and inflexible. A flexible constraint is one that does not require a specific start or finish date. An inflexible constraint is one that does require a specific start or finish date.

Constraint	Description
As Late As Possible	Flexible. A task with this constraint is scheduled so that it can be finished as late as possible, but without delaying any other scheduled task in the task plan. This constraint is the default when a task plan is scheduled from its finish date.
As Soon As Possible	Flexible. A task with this constraint is scheduled so that it begins as early as possible. This constraint is the default when a task plan is scheduled from its start date.
Finish No Earlier Than	Flexible. A task with this constraint must finish on or earlier than the date specified.
Finish No Later Than	Flexible. A task with this constraint type must finish on or after the date specified.
Must Finish On	Inflexible. A task with this constraint must finish on the date specified. All possible task finish date measurements (finish, early finish, and late finish) are given the same finish date.
Must Start On	Inflexible. A task with this constraint must start on the date specified. All possible task start date measurements (start, early start, and late start) are given the same start date.
Start No Earlier Than	Flexible. A task with this constraint cannot start earlier than the date specified.
Start No Later Than	Flexible. A task with this constraint cannot start later than the date specified.