Project Management 101: What is Float/Slack?
In project management, “float” or “slack” is the amount of time that a task can be delayed without affecting the deadlines of other subsequent tasks, or the project’s final delivery date. The former is called “free float”, and the latter is called “total float”.
How Do I Find Float?
The simplest way to compute slack is to subtract the time you’ve allotted to complete a task from the time the task actually takes. For example, if you’ve allotted 10 days for a task, but it only takes you 6 hours to complete, then your slack is 4 days. Tasks that have zero float can be considered as part of the “critical path”, because any delay on these tasks means a delay to the project deadline itself.
To compute total float, you need to add up the free float of all the other tasks in the project. If the number is positive, then you have that much room to finish a project in case of delays or problems. If the number is negative, then you don’t have enough time scheduled for the project and it will most likely miss the deadline.
How Can I Maximize Float?
In order to maximize float, you need to identify your critical path and calculate the amount of float in each non-critical task path. It will help if you visualize the project using a Gantt chart or PERT diagram. With these tools, you can reshuffle tasks and consolidate all of your non-critical tasks into as few task chains as possible. You can then reassign resources and work schedules to focus on the critical chain, and to increase team productivity and efficiency. It may not change the amount of float, but it will get you the most out of those spare hours.
Make sure you revise your float estimates as the project goes on. If one task takes longer than expected, you have the option of using up estimated float from a task further down the calendar. Some project managers add a little bit more float than necessary as a safety measure against unexpected delays.
Of course, there will be circumstances where your project gets delayed no matter how well you manage your float time. Learn from these delays and account for them the next time you schedule a project.
Image credit, Flickr, Kham Tran