Float (Total Float and Free Float)
Total float is the amount of time an activity can be delayed from its early start without delaying the project finish date. Free float is the amount of time an activity can be delayed without delaying the early start of any successor activity.
Explanation
Float (also called slack) measures the scheduling flexibility available for an activity. Understanding float is essential for schedule management because it identifies which activities have room for delay and which are time-critical.
Total float is calculated as Late Start minus Early Start (LS - ES) or Late Finish minus Early Finish (LF - EF). It represents how long an activity can be delayed without affecting the project completion date. Activities on the critical path have zero total float. Activities with positive total float can be delayed by up to that amount without impacting the project end date, though they may affect the timing of non-critical paths.
Free float is the amount of time an activity can be delayed without affecting the early start of any immediately succeeding activity. Free float is always less than or equal to total float. An activity can have total float but zero free float if delaying it would push out a successor's early start (even though it would not delay the project). Project float (also called project slack) is the amount of time the project can be delayed without exceeding an externally imposed completion date.
Key Points
- •Total float: delay allowed without affecting the project finish date (LS - ES or LF - EF)
- •Free float: delay allowed without affecting any successor's early start
- •Critical path activities have zero total float
- •Free float is always less than or equal to total float
Exam Tip
Know the difference between total float and free float. Total float = LS - ES. Free float = ES of successor - EF of current activity. Both are commonly tested.
Frequently Asked Questions
Related Topics
Critical Path Method (CPM)
The Critical Path Method (CPM) is a schedule network analysis technique used to estimate the minimum project duration and determine the amount of scheduling flexibility (float) on the logical network paths within the schedule model.
Critical Path
The critical path is the longest sequence of activities in a project schedule network diagram that determines the shortest possible project duration.
Develop Schedule
Develop Schedule is the process of analyzing activity sequences, durations, resource requirements, and schedule constraints to create the project schedule model for project execution, monitoring, and controlling.
Schedule Compression
Schedule compression is a technique used to shorten or accelerate the project schedule duration without reducing the project scope.
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