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In project management, float or slack is the amount of time that a task in a project network can be delayed without causing a delay to:^{[citation needed]}

• subsequent tasks (free float)
• project completion date (total float)

An activity that has a total float equal to zero is said to be a 'critical activity', which means that a delay in the finish time of this activity will cause the entire project to be delayed by the same amount of time.^{[citation needed]} A critical activity typically has free float equal to zero, but an activity that has zero free float may not be on the critical path.

Consider the process of replacing a broken pane of glass in the window of your home. There are various component activities involved in the project as a whole; obtaining the glass and putty, installing the new glass, choosing the paint, obtaining a tin of paint, painting the new putty once it has set, wiping the new glass free of finger smears etc etc.

Some of these activities can run concurrently e.g. obtaining the glass, obtaining the putty, choosing the paint etc., while others are consecutive e.g. you cannot buy the new paint until you have chosen it, you cannot paint the new putty until the window is installed and the new putty has set. Delaying the acquisition of the glass is likely to delay the entire project - this activity will be on the critical path and have no float, of any sort, attached to it and hence it is a 'critical activity'. A relatively short delay in the purchase of the paint may not automatically hold up the entire project as you still have to wait some time for the new putty to dry before it can be painted anyway - there will be some 'free float' attached to the activity of purchasing the paint and hence it is not a critical activity. However a delay in choosing the paint in turn inevitably delays buying the paint which, although it may not subsequently mean any delay to the entire project, does mean that choosing the paint has no 'free float' attached to it - despite having no free float of its own the choosing of the paint is involved with a path through the network which does have 'total float'.

List of project management topics

This article or section includes a list of references or external links, but its sources remain unclear because it lacks in-text citations. You can improve this article by introducing more precise citations.

• AACE International. "Cost Engineering Terminology, AACE International Recommended Practice No. 10S-90", www.aacei.com, August 2007. 

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