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Understanding the Effects of Project Task Constraints

written by: Ronda Bowen • edited by: Marlene Gundlach • updated: 3/27/2013

This article gives the pros and cons to using task constraints. Learn about flexible and inflexible constraints and how they apply to your project.

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    What Are They?

    Picture courtesy of Stock.xchng Task constraints place restrictions on the ways that start and finish times are calculated in a task. There are flexible and inflexible task constraints. Flexible task constraints aren’t associated with particular dates whereas inflexible constraints are associated with particular dates.The eight typical task constraints are:

    • As Late As Possible (flexible) – Finish the task as late as possible. This constraint is used when the project manager is scheduling the project from the projected finish date.
    • As Soon As Possible (flexible) – Start the task as soon as possible.
    • Finish No Earlier Than – This schedules a task to finish on or after a specific date.
    • Finish No Later Than – This schedules a task to finish on or before a particular date.
    • Must Finish On – This is an inflexible constraint; this constraint is a hard and fast deadline.
    • Must Start On – Another inflexible constraint, this ensures that the task begins on a particular day.
    • Start No Earlier Than – The task will be scheduled to begin on or after the date given here.
    • Start No Later Than – The task will be scheduled to begin on or before the date given here.

    By default every task has the “Start As Soon As Possible” constraint. Because of this, there is never a time when a project doesn’t contain a task constraint. With this constraint, the project manager would not enter in a start or finish date.

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    Pros of Using Task Constraints

    The pros of flexible constraints include the ability to schedule tasks with relative ease – the tasks are scheduled automatically, each picking up where the last left off when they have been marked as dependent upon one another. The project manager does not have to know when the project will be finished, or when particular tasks will be finished or begin, if she uses flexible constraints.

    Inflexible constraints can help maintain the progress of a project. They ensure that there are some hard and fast deadlines. If a report is definitely needed by March 8, then using the “Finish No Later Than” constraint can help ensure this.

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    Cons of Using Task Constraints

    Flexible task constraints are the default for any project – so all projects have them. Flexible constraints on tasks can leave the project feeling like its blowing in the wind and not making real progress. Moreover, if all constraints are flexible, then scope creep can be more of a threat. This is because team members may feel that since there are no real hard and fast deadlines they have all the time in the world. Moreover, constraints such as “Start No Later Than” or “Finish No Later Than” may lead employees to see the “No Later Than” date as the real deadline. Thus it slips into being an inflexible constraint.

    Inflexible task constraints might not be accurately chosen. They could place unnecessary strain on the team. It’s also possible that the “Must Start On” or “Must Finish On” dates don’t match the dates that the task is actually started or finished on.

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    Read More About It

    For more information on tasks and task constraints in projects, read the following BrightHub PM articles by Linda Richter:

    "Project 2007: Working with Task Relationships" and "Project 2007: Setting Task Deadlines"