Best Practice 7: Ensuring Reasonable Total Float

Best Practice 7: The schedule should identify reasonable total float (or slack)—the amount of time a predecessor activity can slip before the delay affects the program’s estimated finish date—so that the schedule’s flexibility can be determined. The length of delay that can be accommodated without the finish date’s slipping depends on the number of date constraints within the schedule and the degree of uncertainty in the duration estimates, among other factors, but the activity’s total float provides a reasonable estimate of this value. As a general rule, activities along the critical path have the least float. Unreasonably high total float on an activity or path indicates that schedule logic might be missing or invalid.

Management should be aware of schedule float. Activities with the lowest total float values constitute the highest risk to completing the schedule or meeting interim milestones. In general, if zero-total-float activities or milestones are not finished when scheduled, they will delay a program the same length as their delayed finish—unless successor activities on the critical path can be completed sooner than originally planned. An activity’s delay causes total float to decrease, thus increasing the risk of not completing the program as scheduled.

Incomplete, missing, or incorrect logic, unrealistic activity durations, and unstatused work distort the value of total float so that it does not accurately represent the schedule’s flexibility. In addition, total float may not be a completely accurate measure of flexibility if the schedule has date constraints or deadlines such that low or even negative float values for activities do not drive the finish milestone. Thus, it is imperative that managers for both the customer and the contractor proactively manage total float as activities are completed. Doing so will ensure that the program schedule accurately depicts the program’s flexibility and enables management to make appropriate decisions in reallocating resources or resequencing work before the program gets into trouble.