Q 621. What is float in context of Critical Path Method (CPM)? How is it calculated and how can a project lead use it to optimize the project timelines? Illustrate your answers with an example.

 

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In Critical Path Method (CPM), float is basically maximum buffer time allowed in the project's planned scheduled without impacting the outcome. Its also called slack meaning no activity time. 

 

There are two types of float, Free float which is the buffer or slack time between the scheduled actions and there is Total float which is the total buffer time allowed. 

 

Project lead can prioritise the critical tasks to ensure zero or minimum float so there is no impact out final outcome and timeline. This way less critical tasks which may have extra float time can be utilise if there are any delays in top priority tasks. This way if there is any slack in task completion, it can be adjusted. 

Float is the difference of Latest start  time/date and Earliest start time/date in a critical path method.

 

In other words , one first needs to determine earliest start time . Latest start time is achieved by subtracting duration from latest finish time (right to left)

Critical path method is where earliest start time and latest finish time are the same.

 

Now the float can help determine whether it is possible to defer a project by few days or not. If activity 1 has an earliest start time of 0 days and latest start time of 2 days, then essentially it tells one that the difference or float of 2 days can be given to the project.

The factor that contributes to the professional credibility of any project lead the most is being able to complete the project on time. Critical Path Method (CTM) is the technique that assists project leads to calculate the timeline and completion date of projects with a high degree of accuracy. Achieving 100% accuracy in this calculation is usually very challenging since various factors , out of the project leads' control, may appear in the project ecosystem. 

 

Examples of factors that are usually out of the project leads' control are :
(1)  important project execution leads may quit their jobs in the middle of the timeline,
(2) delay in talent acquisition , especially, when the skills required for the role are very niche
(3) unforeseen budget constraints in the same or other departments may adversely impact the ongoing projects,
(4) unforeseen cases of major process breach in the same or other departments may impact the project timeline adversely.

 

These factors may induce delays in the project timeline to various degrees but if , while deciding  the project schedule, the project leads include an appropriate degree of flexibility in the timeline then there is high chance of the projects completing on time. This is where 'Float' comes into picture.

 

There are 2 kinds of floats :
(1) Free Float (FF) : The maximum amount of time an activity can be delayed without impacting the early start time of any of its dependent activities.
(2) Total Float (TF): The maximum amount of time an activity can be delayed without impacting the project's completion date.

 

In order to conclude the float, project leads must first decide the early start (ES) and late start (LS) times for every activity. ES is the earliest possible time an activity may begin, while LS is the latest time an activity may begin without delaying the project.
Free Float (FF) for any task , FF = LS - ES - Duration of the task
Total Float (TF) for any task , TF = LFT - EFT - Duration of the task

 

Following are the ways in which project leads may use float in project timeline optimization :
(1) Find out non-critical tasks : if the float of a tasks turns out to be fairly high then it is not critical. In other words, for such tasks the project lead may include enough flexibility in deciding the timeline so that the focus is more on critical tasks.
(2)Assigning resources to high priority tasks : project leads may assign high priority resources to more critical tasks that have less flexibility while lower priority resources to less critical tasks that have high degree of float.
(3) Handling delays that are unpredictable : delays that are unpredictable can be diverted to tasks that have higher flexibility or float . This way the more critical tasks can be executed on time. This helps the project leads to make sure that the project can be delivered on time.
(4) Adjust scope changes : float can help project leads to handle small scope adjustments well. The small delays caused by these scope adjustments can be absorbed by the less critical high flexibility activities. Thus, the small delays do not permeate into the final closure of the project , helping project leads to finish projects on time. 
(5) Negotiating delays with external stakeholders : Float assists project leads to position themselves better when negotiating delays in tasks to be performed by external entities like suppliers or service providers. This helps the leads to make sure that the closure of critical tasks with little to no flexibility are unaffected and so is the completion of the project.

 

Let's look at an example to understand all these factors in a practical scenario :
Project ABC has 5 activities : A (2 days ) , B (5 days) , C (6 days)  , D (3 days) , E (2 days).
Task A is dependent on task B 
Task  B is dependent on task C
Task C is dependent on task D
Task  D is dependent on task E.
We calculate the float and find out that tasks A , B & C have no float while tasks D & E have it. This means that the project lead must make sure that tasks A, B & C must be completed with strict adherence to the decided timeline while any delay caused by any factor can be absorbed by tasks D & E for the project to be completed on time.

Float is a time (Float time) is also referred as slack time that indicates particular tasks that can be delayed without delaying the project deadlines. In float time, scheduling of task becomes more flexible which can be used to offset many risks, if planned properly. Float time is typically presented with no. of days, weeks or month that gives project lead a flexibility on how long a task can wait before proceeding with the subsequent task. In order to make most out of float time, it is crucial for project lead to identify and strategically plan the activities.

Identification of float time improves the productivity of projects as every Project is unique and may involve many complex sequences of tasks, some of these tasks are critical tasks, which means that project lead has to make sure that these tasks are completed in defined timeline.

However, some of the tasks are non-critical tasks which can be done in less time & these tasks do not have any impact on subsequent tasks, the difference in Critical task time and non-critical task time is referred as float time.

 

Below is simple Example of float in CPM: -

 

Activity	Activity Time	Intermediate Predecessor
Start	0	-
A	4	Start
B	6	A
C	6	A
D	5	B
E	7	C, D
End	0	E

 

 

 

 

With reference to above diagram and calculation, it’s important to Identify critical and non-critical activities. Critical activities must be completed within specified timelines to prevent project delays while non-critical activities have some flexibility and by distinguishing between these two, project lead can focus on utilizing float time for non-critical activities without compromising project deadlines.  

Utilization of float time can be determined to understand the potential impact on the project, resources required for meeting timeline of other critical tasks, Engaging resources in Improvement project like process improvement, professional skill development or Innovation activities etc.

Saurabh has given the best answer to the question. Well done!