HKSM
Float
The amount of schedule flexibility for an activity or path, expressed as how long it can be delayed without creating a defined impact. In practice, this flexibility is measured as total float when the impact is the project finish date, or as free float when the impact is the start of the immediate successor.
Key Points
- Also called slack. See total float and free float.
- Calculated via critical path method by comparing early and late dates from forward and backward passes.
- Activities on the critical path typically have zero total float; negative float indicates a schedule that violates an imposed date.
- Float is consumable and can be reduced by changes, risk responses, or resource leveling, so it should be monitored and managed.
Example
In a sequence A -> B -> C, B is planned to finish on day 6 and C is scheduled to start on day 9. B can slip to finish as late as day 9 without delaying C, so B has 3 days of free float. If the project finish depends on C, B also has 3 days of total float.
PMP Example Question
Which statement best describes float in a project schedule?
- The budget reserve available to absorb cost overruns.
- The time an activity can slip before affecting a defined schedule date, such as the project finish or a successor's start.
- The difference between optimistic and pessimistic duration estimates.
- Idle time caused by resource underutilization.
Correct Answer: B — time an activity can slip before affecting a specified schedule date
Explanation: Float represents schedule flexibility; common forms are total float (relative to project finish) and free float (relative to the successor's start).
