Tips for Critical Path, Total Float & Free Float

I would like to start the topics which can bring more fruits with little scope of doubts. If a little attention is paid on these topics, there are very less chances of ambiguity. Yes, you have guessed it right, I will concentrate on the topics with numerical problems.

Today I will talk about the above topics in the subject of the post. Numerical problems are not lengthy and the calculations involved are very simple.

Critical Path - This is the longest duration path in the network diagram but the shortest possible time to complete the project. I am assuming here that you have already prepared the network diagrams and know its basic concepts. Once you have the network diagram ready, look at the each possible path from start to finish, calculate the duration of each path, the path with the longest duration is the critical path. It is possible to have more than one critical paths in a project. More the critical paths riskier the project.

Let's look at an example. Click on the below image to enlarge.





There are three paths -
1. Start-A-C-D-F-H-End = 11 days
2. Start-A-C-E-H-End = 8 days
3. Start-B-G-I-End = 12 days

Path 3 (Start-B-G-I-End) shown in Red is the critical path as this has the longest duration.

Path 1 (Start-A-C-D-F-H-End) is near critical path. A project manager not only should watch out for the critical path but also should concentrate upon the near critical path as this has the potential to become a critical path if not managed well.

Free Float - This is the time by which an activity can be delayed without delaying the early start of its successor activity.

Free float of an activity = (ES of the next activity - EF of that activity) - 1
(Note: -1 is there if you are considering the 1st day of the project as 1 but if you consider the 1st day of the project as 0th day, -1 will be omitted)

Total Float - This is the total time by which an activity can be delayed without delaying the scheduled end date of the project.

Total float of an activity = (LF - EF) of that activity OR (LS-ES) of that activity

Unless specifically asked for free float in questions consider float=total float.

Activities on the critical path have ZERO float.

In the above diagram,

Free Float for activity F = ES of H - EF of F - 1 = 11-10-1 = 0
Total Float for activity F = (LS - ES) of F OR (LF - EF) of F= 11-10 = 1

Free Float for activity E = ES of H - EF of E - 1 = 11-7-1 = 3
Total Float for activity E = (LS - ES) of E OR (LF - EF) of E = 11-7 = 4

20 comments:

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    ReplyDelete
  2. how then do you calculate the free float of an activity and total float of activity that has all equal LFT's AND EST's

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  3. thanks for the information regarding CPM. Its very handy...

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  4. Can you please show using the same network diagram which path can be use to compress the scedule, this has been asked in the exam & i was confused to answer...could you please

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    Replies
    1. Nice job! It will help if you can add dates or make the formula more elaborate.

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  5. this info is very useful however, i would like to know which software did you use to make this diagram as i have my project, where it asks us to use this similar kind of netwrk diagram.

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  6. A great article which grasp me to understand the topic.
    Cheers!

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  7. When I calculated the CP, two paths actually are critical. Any explanations?

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  8. I have a question that i have been trying to work out but can't seem to get it right. the question is about drawing a network diagram and calculating the critical path and the total float

    if there is anyone willing to help please email me on veroneca.mpofu@gmail.com

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  9. Total float for F is calculated incorrectly.
    It has to be 11-9=2 or 12-10=2 .. it is incorrectly mentioned as 1.. Other than that, superb article....!!!

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    Replies
    1. how are you saying It is incorrect, i guess as per the formulae LS - ES or LF - EF it has to be 1 and it is correct ?

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  10. many thanks for the free float example.
    in the diagram, if add date in start/end and use start = 0 to demo, it would be easier to understand.

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  11. thanks...helpful

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  12. "Thank You

    The given information PMP tips is very effective
    i will keep updated with the same
    "

    ReplyDelete
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  14. simple language and very informative to understand..

    ReplyDelete