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15 January 2011

What is Slack? What is Float? Is There A Difference?

David A. Zimmer
David A. Zimmer, PMP
Chief Project Professor
American Eagle Group

PMBOK® Guide Definition:

Slack: Also called Float. See Float.
Float: Also called Slack. See Slack.

Total Float: The total amount of time that a schedule activity may be delayed from its early start without delaying the project finish date, or violating a schedule constraint. Calculated using the critical path method technique and determining the difference between the early finish dates and late finish dates. See also Free Float.

Free Float: The amount of time that a schedule activity can be delayed without delaying the early start date of any immediately following schedule activities. See also Total Float.

Practical Definition:

Slack or Float provide flexibility in the project schedule. When leveraged properly, project managers can shift activities and resources to meet the project objectives and priorities. It is the amount of time an activity can be delayed without impacting other activities or the project end date and changes over the course of the project implementation.

So, What Is Slack or Float?