Free Float
The maximum time an activity can slip without pushing the early start of any successor or breaking a schedule constraint.
Key Points
- Free float is measured for a single activity relative to its immediate successors.
- Computed as the earliest successor's early start minus the activity's early finish, adjusted for leads/lags and constraints.
- If a successor is scheduled to start as soon as this activity finishes, the free float is zero.
- Different from total float, which is based on the overall path or project finish date.
Example
Activity B finishes (EF) on day 8. Its earliest successor, Activity C, has an early start (ES) on day 10. Free float for Activity B is 2 days (10 - 8). B can be delayed up to 2 days without delaying C's early start or violating any schedule constraint.
PMP Example Question
Which statement best describes free float?
- The total time an activity can slip without delaying the project completion date.
- The time an activity can be delayed without delaying the early start of any successor or violating a schedule constraint.
- The slack available to the entire network path on which the activity lies.
- The extra time created by assigning additional resources to an activity.
Correct Answer: B — The time an activity can be delayed without pushing a successor's early start or breaking a constraint
Explanation: Free float looks only at the relationship between an activity and its successors, not the overall project finish or full path slack.