project management geeks float

How to calculate float after critical path?

Few week ago, we shared a superb easy guide to calculate a critical path in six easy steps. If you have followed that guide and successfully able to find the critical path, we highly recommend you to calculate float by carrying same critical path method. Before directly jumping to maths for determining float, we would like to share some other important information which can be useful for you being a project manager of any career level.

Is there any difference in word “Float” and “Slack”?

Absolutely No! There is no difference between Float and Slack except spellings. They are the same thing. If you ever try to certify yourself as PMP® from PMI, you will find Slack written in their official training material as well as exam. For now, just put in your mind that Float = Slack and Slack = Float.

What are types of float?

There are three types of floats and each one has minor different among all. Let’s view the definition of each float type from high level:

Total Float – Total float is the time that an activity can be delayed without bringing any impacts on project’s finish date. It will give you a room to play before project gets delayed.

Free Float – Guess, you have two or more activities having a common successor. Free float will give you the time an activity can be delayed without impacting the early start date of its successor.

Project Float – That’s something for management or customer. It means the amount of time a project can be delayed without impacting imposed dates by the customer or management. (yes it happens, see a real example below).

A customer signed up with our organization to integrate one of the giant money exchange company so they can bring remittances. They tied up a festival month as Go Live date to capture the maximum remittances. They signed the contract with us 6 months before and efforts were required to integrate the money exchange was 2 months. Now do maths!

Project Float = 180 (Customer given deadline) – 60 (Our Efforts) = 120 days!

Benefits of Calculating Float?

Importantly, you should know that why to calculate float and exactly where it is going help you. Being a project manager, you should know your cushions with each activities along with it’s impacts on overall target date of project so you can tackle emergencies, delays and issues. Furthermore, you can also take time to improve quality of your deliverable if high float is available.

In large and complex projects where number of activities are big in size, you will need to use a tool like MS Project to make your life easier and paper free 🙂

Zero float usually represents the critical activities in project. Project becomes risky and single point of failure will be created that will delay the whole project if not managed properly.

Now, Let’s Calculate Float

Calculate float by using Precedence diagram is much easier, so we going to cover Precedence Diagram method in this tutorial. For other methods, you can specifically ask in comments section on through contact form.

Here is the sample precedence diagram covering real example from our project library.

project management geeks float

There are three paths in above diagram and by looking at the duration of each path you can identify the critical path. In this case, Path 1 duration = 7+14+15+10 = 46 days, Path 2 duration = 7+14+6+10 = 37 days and Path 3 duration = 7+14+5+4+3+7+10 = 50 days. So critical path in above picture is Path 5, means we have to calculate float for each activity resides in Path 1 and Path 2.

To calculate the float for non critical path activities, you must identify the next longest path and then minus its duration from duration of the critical path. Confuse? Put values in following formulae you will have the float:

Float for Path 1 = Duration of Critical Path – Duration of Path 1

= 50 – 46 = 4 days.

Float for Path 2 = Duration of Critical Path – Duration of Path 2

= 50 – 37 = 13 days.

Float for each activity lie on Path 1 will be 4 days and Path 2 will be 13 days except Initiating & Planning as both are related to Critical Path as well.

Learn how to present / display float?

You have learned how to calculate float, but communicating numbers to management will not be a good ideas as per top management communications approaches. Float results should be presented like serious threats or opportunities with brief descriptions. For instance, you can write in your report that, “Although module 2 can be delayed, not more than 4 days to avoid impacts on projects.”

Was not it a easiest way to determine float after critical path? We are sure that you must have got some great methods and would like to hear back those in comments section of this post. You can also share your feedback and suggestions on our contact form too.

One comment

  1. A couple of thoughts … float and slack are different. Slack has to do how long the start of an activity can be delayed while float pertains to how long its finish can be delayed. The numbers are the same in most simple examples, but when you get to real projects with calendars, they are often different.

    Calculating slack or float from the path durations only works when there are no interconnections among the paths. In the examples above, add Modules 1A, 1B, 2A, and 2B with durations of 3 days each. Then connect 1A to 3B and 2B to 3C. Even ignoring calendars so that float and slack are equal, you’ll have to calculate it for each activity by subtracting ES from LS or EF from LF.

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