Critical Path Analysis (CPA) is a project management technique that helps identify the critical tasks and the amount of time required to complete them. Two important concepts in CPA are Total Float and Free Float. In this article, we will be discussing total float vs free float. 

What is Total Float?

Total Float refers to the amount of time that a task can be delayed without affecting the completion date of the project. It is the difference between the estimated duration of the task and the latest possible start date. Total float can be calculated for each task in the project and helps project managers identify tasks that can be delayed without causing any delays to the overall project completion.

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How to Calculate Total Float? 

Total float is the amount of time a scheduled activity can be delayed without delaying the overall project completion date. To calculate total float, you can use the following formula:

Total float = Late finish - Early finish

Where "Late finish" is the latest possible finish date for an activity and "Early finish" is the earliest possible finish date for an activity. These values can be obtained through critical path analysis or network diagramming.

Total Float Examples 

Here are some examples to help you understand the calculation of total float:

Consider a project with the following activities and their duration:

Activity A: 5 days

Activity B: 3 days

Activity C: 4 days

Activity D: 2 days

The critical path for this project is A, B, and C (5+3+4 = 12 days). The early finish time for each activity can be calculated as follows:

Activity A: Early Start + Duration = 0 + 5 = 5

Activity B: Early Start + Duration = 5 + 3 = 8

Activity C: Early Start + Duration = 8 + 4 = 12

Activity D: Early Start + Duration = 8 + 2 = 10

The late finish time for each activity can be calculated as follows:

Activity A: Late Start + Duration = 12 - 5 = 7

Activity B: Late Start + Duration = 7 - 3 = 4

Activity C: Late Start + Duration = 4 - 4 = 0

Activity D: Late Start + Duration = 12 - 2 = 10

The total float for each activity can be calculated as follows:

Activity A: Late Finish - Early Finish = 7 - 5 = 2 days

Activity B: Late Finish - Early Finish = 4 - 8 = -4 days

Activity C: Late Finish - Early Finish = 0 - 12 = -12 days

Activity D: Late Finish - Early Finish = 10 - 10 = 0 days

Consider another project with the following activities and their duration:

Activity X: 6 days

Activity Y: 4 days

Activity Z: 3 days

The critical path for this project is X, Y, and Z (6+4+3 = 13 days). The early finish time for each activity can be calculated as follows:

Activity X: Early Start + Duration = 0 + 6 = 6

Activity Y: Early Start + Duration = 6 + 4 = 10

Activity Z: Early Start + Duration = 10 + 3 = 13

The late finish time for each activity can be calculated as follows:

Activity X: Late Start + Duration = 13 - 6 = 7

Activity Y: Late Start + Duration = 7 - 4 = 3

Activity Z: Late Start + Duration = 3 - 3 = 0

The total float for each activity can be calculated as follows:

Activity X: Late Finish - Early Finish = 7 - 6 = 1 day

Activity Y: Late Finish - Early Finish = 3 - 10 = -7 days

Activity Z: Late Finish - Early Finish = 0 - 13 = -13 days

Note: The total float is calculated based on the assumption that all activities are executed one after the other and there are no concurrent activities.

What is Free Float? 

Free Float, on the other hand, refers to the amount of time that a task can be delayed without affecting the start date of its subsequent tasks. It is calculated as the difference between the earliest possible start date of the next task and the latest possible finish date of the current task. Free float helps project managers understand the amount of slack available in the project schedule.

How to Calculate Free Float? 

Free float is the amount of time an activity can be delayed without delaying the start of its successor activity. To calculate free float, you can use the following formula:

Free float = Early start of the successor activity - Early finish of the current activity

Where "Early start of the successor activity" is the earliest possible start date for the next activity in the network and "Early finish of the current activity" is the earliest possible finish date for the current activity. These values can be obtained through critical path analysis or network diagramming.

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Free Float Examples 

Here are some examples to help you understand the calculation of free float:

Consider a project with the following activities and their duration:

Activity A: 5 days

Activity B: 3 days

Activity C: 4 days

Activity D: 2 days

The critical path for this project is A, B, and C (5+3+4 = 12 days). The early finish time for each activity can be calculated as follows:

Activity A: Early Start + Duration = 0 + 5 = 5

Activity B: Early Start + Duration = 5 + 3 = 8

Activity C: Early Start + Duration = 8 + 4 = 12

Activity D: Early Start + Duration = 8 + 2 = 10

The early start time for each activity can be calculated as follows:

Activity B: Early Finish - Duration = 5 - 3 = 2

Activity C: Early Finish - Duration = 8 - 4 = 4

Activity D: Early Finish - Duration = 10 - 2 = 8

The free float for each activity can be calculated as follows:

Activity A: Early Start of the Successor - Early Finish = 2 - 5 = -3 days

Activity B: Early Start of the Successor - Early Finish = 4 - 8 = -4 days

Activity C: Early Start of the Successor - Early Finish = 8 - 12 = -4 days

Activity D: Early Start of the Successor - Early Finish = N/A (Activity D is the last activity in the network)

Consider another project with the following activities and their duration:

Activity X: 6 days

Activity Y: 4 days

Activity Z: 3 days

The critical path for this project is X, Y, and Z (6+4+3 = 13 days). The early finish time for each activity can be calculated as follows:

Activity X: Early Start + Duration = 0 + 6 = 6

Activity Y: Early Start + Duration = 6 + 4 = 10

Activity Z: Early Start + Duration = 10 + 3 = 13

The early start time for each activity can be calculated as follows:

Activity Y: Early Finish - Duration = 6 - 4 = 2

Activity Z: Early Finish - Duration = 10 - 3 = 7

The free float for each activity can be calculated as follows:

Activity X: Early Start of the Successor - Early Finish = 2 - 6 = -4 days

Activity Y: Early Start of the Successor - Early Finish = 7 - 10 = -3 days

Activity Z: Early Start of the Successor - Early Finish = N/A (Activity Z is the last activity in the network)

Note: The free float is calculated based on the assumption that all activities are executed one after the other and there are no concurrent activities.

Total vs Free Float 

Total Float is the total amount of time a task can be delayed and still keep the project on schedule, while Free Float is the amount of time a task can be delayed without impacting other tasks in the project. Here's an example to illustrate the difference between Total Float and Free Float:

Suppose you have a project with three tasks: A, B, and C.

Task A is estimated to take 2 days to complete, task B is estimated to take 3 days to complete, and task C is estimated to take 5 days to complete.

If task A starts on Monday, it will finish on Tuesday, and task B will start on Wednesday and end on Friday. Task C will start on Saturday and end on the following Wednesday.

The Total Float for task A would be 0 days, as any delay in completing task A would affect the start of task B and therefore the overall project completion date.

The Free Float for task A would be 1 day, as it could be delayed by 1 day without affecting the start of task B.

The Total Float for task B would be 2 days, as it could be delayed by 2 days without affecting the overall project completion date.

The Free Float for task C would be 0 days, as it is the last task in the project and any delay would affect the overall project completion date.

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Total Float vs Free Float - Final Verdict 

Both Total Float and Free Float play a crucial role in project management and help project managers make informed decisions. For example, if a task has a high total float, the project manager can decide to delay it and allocate resources to other critical tasks. Similarly, if a task has a high free float, the project manager can decide to reschedule it to reduce the overall project duration.

Other Time Management Concepts 

Duration vs Effort

When we are estimating the time required to complete an activity, we use the words effort, duration etc. Is duration and effort the same? NO.

Effort is the actual amount of time spent to carry out an activity. This can be expressed in terms of person hours, man days or man months. It shows the total number of hours/days/months that each person spent working on each of the activities.

Duration is the amount of time taken to carry out an activity. That is the start time and end time which is nothing but the time elapsed to complete the activity. Duration is measured in hours/days etc. This doesn’t count the number of people working on the activity.

For example: An activity takes 4 hours to work by one person.  The person who is carrying out this activity contributes one hour per day. So the total days taken will be 4 days. Here the effort is 4 hours whereas the duration is 4 days.

Crashing vs Fast tracking

After the arrival of the total duration of the project by estimation technique, the project manager presents the schedule to the PMO/Sponsor/Customer.  But the Customer says that the duration has to be reduced without compromising on the scope of the work. Now what is the left out option for Project Manager, either he/she has to add resources or has to run the activities in parallel.

Crashing is nothing but adding resources. Of course when the crashing happens, the cost increases, because you are adding extra resources.

Fast tracking represents the activities to be carried out in parallel instead of series. Here the disadvantage is that, it increases the risk in the area of may be quality as the activities are performed parallel.

[Related: Learn the difference between Fast tracking and Crashing]

Forward Pass vs Backward Pass

After the arrival of the critical path in the given network diagram, we need to track closely the activities which are coming under the critical path. And for the activities which are not in the critical path the tracking can be the normal way. But when we say normal, we need to know the degree of the level. This can be determined by the parameter called float or slack. To find the float or the slack we have to perform the Forward pass and Backward pass.

Forward pass is moving through the network diagram from start to finish and covering all the paths.

Backward pass is moving through the network diagram in the reverse way or from Finish to the start of the network diagram and covering all the paths.

When we do the forward and backward pass, we will end up with values of Late Start (LS), Late Finish (LF), Early Start (ES) and Early Finish (EF).

Float is the difference of LS and ES or LF and EF, i.e. LS-ES or LF-EF.

Lead vs Lag

Lead is advancing an activity in terms of schedule to overcome the risk if anything that may happen to the project.

For example: You need equipment 20 days from now and you are importing from outside. Assume that it takes 15 days from the day of order. Instead of waiting for 5 more days from now, order now itself so that you can avoid the possible delay. That is advancing the order day by 5 days.

Lag is deliberately delaying the successor activity.

For Example: There are two activities. The first one is painting and the second one is framing. After painting it will give some time so that the paint will dry and then only will start framing. Deliberate delay in the successor activity is called Lag.

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Conclusion

In conclusion, Total Float and Free Float are important concepts in Critical Path Analysis that help project managers make informed decisions about task scheduling and resource allocation. By understanding the amount of float available in the project schedule, project managers can optimize project completion time, reduce project risk, and ensure the success of the project. You can master this technique along with other project management concepts in our PGP Project Management Training Course . You can also check our PMP® Certification Training. Enroll now and start your journey as a Project Manager today!

FAQs

1. Is total float greater than Free Float?

No, Total Float is not always greater than Free Float. Total Float represents the amount of time that a task can be delayed without affecting the completion date of the project, while Free Float represents the amount of time that a task can be delayed without affecting the start date of its subsequent tasks. Depending on the task and the project schedule, Free Float can be greater than, equal to, or less than Total Float.

2. What is the total and Free Float difference?

The difference between Total Float and Free Float is that Total Float represents the amount of time a task can be delayed without affecting the completion date of the project, while Free Float represents the amount of time a task can be delayed without affecting the start date of its subsequent tasks.

In other words, Total Float is a measure of the overall flexibility in a project schedule, while Free Float is a measure of the flexibility at the task level. Total Float takes into account the entire project schedule and all interdependencies between tasks, while Free Float focuses on the individual task and its relationship to the tasks that follow it.

Therefore, while Total Float gives a general picture of the amount of time available for a project to be delayed, Free Float provides a more detailed and specific view of the amount of flexibility available for each individual task.

3. How do you calculate FF and TF?

Free Float (FF) and Total Float (TF) can be calculated as follows:

Free Float (FF):

FF = Early Start of Next Task - Late Finish of Current Task

Total Float (TF):

TF = Late Finish of Task - Early Finish of Task

or

TF = Late Start of Task - Early Start of Task

Here, the "Early Start" and "Early Finish" represent the earliest possible dates that a task can start and finish, taking into account all preceding tasks and task dependencies. The "Late Start" and "Late Finish" represent the latest possible dates that a task can start and finish without delaying the overall project completion date.

The calculation of FF and TF requires knowledge of the project schedule, including task durations, task dependencies, and resource availability. It is important to update the FF and TF calculations regularly as the project progresses, as changes to the project schedule can impact their values.

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