In project management, maintaining the schedule is just as crucial as controlling the budget. Delays in the project can happen due to various reasons, but understanding how to manage this is an important part. This is where the concept of float or slack becomes valuable. Float not only allows delays in scheduling but also helps project managers set task priorities, use resources more efficiently, and handle unexpected changes. In this blog, we will explore the types, calculations, examples, and some best practices of float in detail for the better management of projects.
Table of Contents:
What is Float?
Float is defined as the available time buffer for a task. This value shows how much a task can be delayed without affecting the overall project deadline. The overall delivery date is the main goal of the project. Float helps distinguish between tasks that can be delayed and those that directly impact performance goals in project delivery. This is similar to a performance appraisal system, where timing and evaluation criteria must align for accurate assessment.
There are two types of float:
Float is mainly provided in the Critical Path Method (CPM) scheduling. Tasks in the critical path will have zero float, which means that the task cannot be delayed further without affecting the project deadline or delivery date.
Importance of Float in Project Management and CPM
- Float allows project managers to identify which activities have scheduling flexibility and which must be completed on time to avoid project delays.
- Float allows project managers to identify the critical path of project schedules more effectively.
- Total float shows how much delay can be taken without affecting the finish date of the project.
- Free float shows how much scheduling flexibility can be given without affecting future tasks.
- This enables project managers to more effectively apply proactive planning, make informed decisions, and utilize essential technical skills in today’s dynamic project environments.
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What is Total Float?
Total float indicates how long the project manager can postpone a task without affecting the project delivery date. Total float is one of the most important aspects of the Critical Path Method (CPM), as it indicates to the project managers where they can incur a delay and where they cannot delay.
For example, consider a development project that has to be completed within 30 days. Task A (Designing a homepage) can be done in 5 days and is scheduled in the first week. Task B (Writing content for the homepage) depends on the previous task and requires 4 days. If task B does not start until day 10, there is some float in task A. That float is total float.
How to Calculate Total Float?
There are 2 ways to calculate the total float:
Total float = Latest start time (LS) - Earliest start time (ES)
(or)
Total float = Latest finish time (LF) - Earliest finish time (EF)
Based on the data and requirements, any of the formulas can be used since they will give the same result.
Parameters:
- Earliest start (ES): The possible earliest time that the task can be started.
- Latest start (LS): The latest a task can start without delaying the project.
- Earliest finish (EF): ES + the duration of the task.
- Latest finish (LF): The latest a task can finish without delaying the project.
Total Float Example
Assume the following values apply to a task:
- ES: Day 3
- LS: Day 5
- EF: Day 8
- LF: Day 10
The total float can be calculated by:
- Total Float = Latest Start – Earliest Start = 5 – 3 = 2 days
- Total Float = Latest Finish – Earliest Finish = 10 – 8 = 2 days
This indicates that the task can be delayed by 2 days without affecting the deadline of the project.
What is Free Float?
Free float describes how long a task can be delayed without affecting the start date of its immediate successor task. It is helpful to manage flexibility at the task level and to keep a smooth workflow between dependent activities. Free float looks more at flexibility for project management (the entire project), while total float operates more on local flexibility related to two tasks that are linked.
For example, let’s say a project is to develop a mobile application. Task A (Wireframe Creation) lasts 4 days and starts on Day 2 and ends on Day 6. Task B (UI Design) is dependent on the previous task, has to start on Day 8. You could delay Task A by 2 days (Day 6 to Day 8) without delaying Task B. Those 2 days are considered free float, which allows the project manager the ability to make short-term changes without interfering with the next project task.
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How to Calculate Free Float?
The free float can be found by the following formula:
Free float = Earliest start of next task - Earliest finish of current task
Parameters:
- Earliest finish (EF): The earliest possible time that the current task can be finished.
- Earliest start (ES): The earliest possible start time for the subsequent dependent task.
Free Float Example
Assume there are two tasks to complete:
Task A
- Duration: 4 days
- Earliest start: Day 2
- Earliest finish: Day 6 (4+2)
Task B (Next task of Task A)
Now, the free float can be calculated by
Free float = Earliest start Task B – Earliest finish of Task A = 8- 6 = 2 days
This indicates that task A has 2 days of free float, which means that it can be delayed for 2 days without affecting the start of task B.
Difference Between Free Float and Total Float
| Parameter |
Free Float |
Total Float |
| Definition |
Free float represents the length of time an activity can be delayed without delaying the start of the activity’s immediately following task. |
Total float represents the length of time an activity can be delayed without delaying the overall project finish date. |
| Impact |
Affects only the next dependent activity, not the overall timeframe for the project. |
Affects the complete schedule for the project and may impact the final delivery date as well. |
| Critical Path Relationship |
Tasks can still have free float even if they aren’t on the critical path. |
Tasks on the critical path have zero total float. |
| Use case |
It is used to assess local flexibility between the linked tasks. |
It is used to assess total schedule flexibility and overall project interruptions. |
| Tasks |
Free float is dedicated only to that single task and its subsequent tasks. |
Total float is available to share across multiple parallel tasks, so a delay in one task might affect others. |
| Resource management |
Facilitates task-specific timing management; the successor start time is not impacted. |
Facilitates reallocate of resources between critical tasks and non-critical tasks. |
| Risk level |
Using free float can delay only the next activity, not the complete schedule. |
Using total float can delay the complete schedule if not managed properly. |
| Tools |
Free float is not always automatically shown. It has to be manually calculated as a custom parameter in MS Project, Primavera P6, or ProjectLibre. |
Most project management tools, including Microsoft Project, Primavera P6, and Smartsheet, show total float by default. |
| Support in the decision |
Used when we need to do sequence optimization. |
Helpful for overall planning and indirect project control decisions. |
| Formula |
Free Float = Earliest Start of next task – Earliest Finish of current task. |
Total Float = Latest Start – (Earliest Start or Latest Finish) – Earliest Finish. |
| Example Scenario |
If Task A finishes on Day 5 and Task B starts on Day 8, Task A has a free float of 3 days. |
If Task A has a total float of 3 days, you can delay it by up to 3 days without delaying the project end date. |
Advanced Float Concepts in Project Management
1. Negative Float
Occurs when a task has already finished late. This specifies the amount of time in which the task has to be completed. For example, if a task is supposed to start on Day 10 but is delayed and can only start on Day 12, it has already exceeded its allowable delay. In this case, the task has a float of -2 days.
2. Independent Float
The amount of time a task can slide backwards in time, assuming that the predecessor tasks are finished at their latest finish time, and all the successor tasks are scheduled to start at their earliest times.
Independent Float = Max (0, ES(successor) - LF(predecessor) - Duration)
3. Shared Float
This occurs when multiple tasks occur at the same time or use the same float time. A delay to one task affects the float time of any other tasks that share that float.
Common Mistakes and Solutions to Avoid Them
1. Confusing total float with free float.
Solution: Learn and use the definitions and implications – total float applies to the project schedule, free float only identifies time that affects the next dependent task.
2. Assuming all project tasks are going to have float.
Solution: Identify your critical path first. Tasks on the critical path have zero float, and attention has to be given to those tasks.
3. Miscalculation of float, due to volition use of dependencies
Solution: Before calculating the float, cross-verify the task dependencies. Use tools like Asana for more accuracy.
4. Treating float as extra time instead of flexibility in scheduling.
Solution: Teach your team that float is no longer available once you have used it, and it must be managed, not wasted.
5. Not re-evaluating and updating float figures as a project progresses.
Solution: Regularly recheck the float during project updates to keep it as accurate and up to date as possible.
Best Practices
1. Update your schedule: As the work progresses, update the float values.
2. Use project and resource management software: Programs like Microsoft Project, Primavera P6, or Asana will automatically calculate float.
3. Monitor your critical path closely: Critical tasks are the tasks with zero float and are the most risky in terms of time.
4. Use your float on resource-optimizing activities: Put more resources on critical tasks with float than on other non-critical activities.
5. Communicate float: Tell your team how the float will and won’t impact their timelines and responsibilities.
Conclusion
Float acts as a tool in helping project managers to bring clarity and take charge of complex timelines. Understanding the difference between total float and free float helps project managers see where they have flexibility in the schedule. It also helps manage task dependencies without delaying the overall project deadline. Knowing how to find and use each of these floats gives project managers the ability to find critical tasks and shift resources. Regardless of the project scale, whether you’re carrying out a small project or managing a large-scale initiative, understanding float is an important step towards an on-time, efficient project delivery.
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Free Float vs Total Float – FAQs
Q1. What is the difference between float and slack?
They are effectively the same concept in project management. Float and Slack can be used interchangeably.
Q2. Can a float be negative?
Yes, negative float indicates a task is behind schedule and the task must be fast tracked to meet the project completion date.
Q3. Why is float important in the Critical Path Method (CPM)?
Float allows the planner to see which activities are critical and provides control over the project.
Q4. Do all tasks have float?
No, the tasks on the critical path have zero float.
Q5. Is it ok to use up float time?
Yes float can be spent, however, it needs to be spent wisely. The more float supplied, the less time there is to deal with delays, and may affect the completion of other tasks.