Total Float vs. Free Float in Construction Projects.
In project management, particularly in scheduling, total float and free float are crucial concepts used to understand time flexibility in a project. Both types of float measure how much delay can be tolerated without affecting subsequent tasks or the overall project completion. Understanding these terms is essential for effective scheduling and avoiding delays.
1. Total Float
Total float is the amount of time that a project task or activity can be delayed without affecting the project’s overall completion date. It provides flexibility within the schedule, allowing certain tasks to be delayed without causing the entire project to run behind schedule.
Key Points About Total Float:
- Impact on Project Completion: If a task exceeds its total float, the project’s end date will be delayed.
- Calculation: Total float is calculated by subtracting the task’s early start (ES) from its late start (LS) or its early finish (EF) from its late finish (LF): Total Float=Late Start−Early StartorLate Finish−Early Finish\text{Total Float} = \text{Late Start} – \text{Early Start} \quad \text{or} \quad \text{Late Finish} – \text{Early Finish}Total Float=Late Start−Early StartorLate Finish−Early Finish
- Critical Path: Activities on the critical path have zero total float. Any delay in these tasks will directly delay the project completion.
- Task Flexibility: Tasks with total float can be delayed up to a certain point without impacting the project deadline, offering flexibility in managing resource allocation or delays in non-critical tasks.
Example of Total Float:
Consider a project task that is scheduled to start on day 5 and must finish by day 12, but can be delayed until day 15 without affecting the project. The total float for this task is:Total Float=15 (Late Finish)−12 (Early Finish)=3 days\text{Total Float} = 15 \text{ (Late Finish)} – 12 \text{ (Early Finish)} = 3 \text{ days}Total Float=15 (Late Finish)−12 (Early Finish)=3 days
This means the task can be delayed by up to 3 days without delaying the project.
2. Free Float
Free float is the amount of time a task can be delayed without delaying the start of any immediate succeeding activities. Unlike total float, which looks at the entire project timeline, free float is more specific to individual tasks and their immediate successors.
Key Points About Free Float:
- Impact on Subsequent Tasks: Free float shows how much a task can be delayed without affecting the start of the next task in sequence.
- Calculation: Free float is calculated by subtracting the task’s early finish from the early start of the next activity: Free Float=Earliest Start of Successor−Early Finish of Current Task\text{Free Float} = \text{Earliest Start of Successor} – \text{Early Finish of Current Task}Free Float=Earliest Start of Successor−Early Finish of Current Task
- Local Flexibility: Free float provides flexibility on the level of individual tasks and their immediate dependencies, offering insight into the task’s relationship with its successors.
- Does Not Affect Project Deadline: Delays within the free float period won’t delay the project or any other unrelated activities.
Example of Free Float:
If a task finishes on day 10 and its succeeding task is scheduled to start on day 14, the free float for the first task is:Free Float=14 (Successor’s Early Start)−10 (Current Task’s Early Finish)=4 days\text{Free Float} = 14 \text{ (Successor’s Early Start)} – 10 \text{ (Current Task’s Early Finish)} = 4 \text{ days}Free Float=14 (Successor’s Early Start)−10 (Current Task’s Early Finish)=4 days
The first task can be delayed by 4 days without delaying the next task.
Key Differences Between Total Float and Free Float
| Aspect | Total Float | Free Float |
|---|---|---|
| Definition | Time an activity can be delayed without delaying the project. | Time an activity can be delayed without delaying the next task. |
| Scope of Impact | Affects the entire project completion date. | Affects only the immediate successor activity. |
| Relationship with Critical Path | Not applicable to activities on the critical path (zero total float). | Can exist for activities not on the critical path. |
| Calculation | Late Start – Early Start, or Late Finish – Early Finish. | Successor’s Early Start – Current Activity’s Early Finish. |
| Flexibility | Overall project flexibility. | Localized flexibility between tasks. |
Conclusion
Total float and free float are both essential for managing a project’s schedule flexibility. Total float focuses on the overall project, while free float is more specific to the relationship between tasks. Understanding these two concepts helps project managers control delays, allocate resources efficiently, and make informed decisions to keep the project on schedule.