Project float, also known as slack, is the amount of time by which a given task within a project can be delayed before it impacts the deadline for the project.
Project managers and developers use project float time to schedule the specific timing of tasks as well as the time frames for making decisions to best ensure that projects come in on time. Total float is the span of time between the target end date of the last task on the critical path and the target date for project completion. Free float is the time an individual task can be delayed before impacting the task that follows it, defined as the difference between the task’s earliest and latest possible finish dates.
Float can allow more time for working on a task when necessary. Otherwise, resources can be repurposed for another task. Employees working with multiple teams can put more time into other tasks that are lagging.
Total float is often represented as a positive or negative number representing the number of days. Negative float, also known as negative slack, is the amount of time beyond a project’s scheduled completion that a task requires.
Total float is associated with the path. If a project network chart/diagram has 4 non-critical paths then that project would have 4 total float values. The total float of a path is the combined free float values of all activities in a path.
The total float represents the schedule flexibility and can also be measured by subtracting early start dates from late start dates of path completion. Float is core to critical path method, with the total floats of noncritical activities key to computing the critical path drag of an activity, i.e., the amount of time it is adding to the project’s duration.
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.