Float Management

Total and free float calculations are fundamental products of CPM scheduling. Network logic, float, durations, and criticality of activities are interrelated. That is, the logical sequence of activities and resource assignments within a network dictate the amount of available float, and the amount of available float defines the criticality of an activity to a constrained milestone or to the final milestone, whether constrained or not. Therefore, management cannot correctly monitor the critical path without also monitoring float. Incorrect float estimates may result in an invalid critical path and an inaccurate assessment of program completion dates. In addition, inaccurate values for total float result in a false depiction of the program’s true status, which could lead to decisions that jeopardize the project.

To support on-time completion of a program, management must understand the amount of time an activity can or cannot be delayed. Accurate values of total float can be used to identify activities that could be permitted to slip and resources that could be reallocated. This knowledge helps in reallocating resources optimally and in identifying the activity sequences that should be managed most closely. However, management must also balance the use of float with the fact that total float is shared along a path of activities. Allowing an activity to consume total float prevents successive activities from being able to slip and spends the schedule’s flexibility rather than conserving it for future risks.

Free float is particularly important in leveling resources because leveling generally targets activities with free float first. That is, delaying an activity within its available free float will not affect its successor activity or the program’s completion date. Delaying an activity that has total float but no free float does not affect the project’s completion date but does disturb successor activity dates that rely on the start or finish of the delayed activity. This, in turn, may disrupt resource availability for assignments along the entire path of successor activities.

Once critical path float has been exhausted, the program is on a day-for-day schedule slip. Float on the critical path should be commensurate with program risk, urgency, technological maturity, complexity, and funding profile. Periodic reports should routinely report the amount of float consumed in a period and remaining on the critical and near-critical paths. A portent of things can be seen in the consumption of free float. As a program schedule becomes less flexible, the probability of having to consume near-critical path and critical path float is increased.