Critical Path : is a combination of activities that, if any are delayed, will delay the project’s finish date.
Purpose of critical path method:
1. To calculate the project’s finish date.
2. To identify how much individual activities in schedule can slip with delaying project
3. To identify the activities with the highest risk that cannot slip without changing the project finish date.
Float Calculation using CPM
● Float is the amount of time an activity can be delayed without delaying the project end date.
● Float is always Zero on Critical Path activities.
● Critical Path is longest path of network diagram.
Each activity have same box
ES : Early Start
EF : Early Finish
LS: Late Start
LF : Late Finish
Float = LS-ES or LF-EF
Late Start(LS) – Early Start(ES)
Late Finish(LF) – Early Finish (EF)
You are the project manager of project at SkillsMag and following activities are identified along with the activity effort.
|Activity||Preceding Activity||Duration (Wks)|
First prepare schedule network Diagram
Calculate the ES and EF of each activity using forward pass technique.
Remember the following formulas for calculation.
Early Start (ES) = Early Finish(EF) of Predecessor activity. If no predecessor activity exists then 0.
Early Finish (EF) = Early Start (ES) + Activity Duration
Activity E is highlighted as it has 2 predecessor activities. we take higher one.
Under this technique, we will start calculating the value from last activities on the path i.e. from G,H and I.
Thumb Rule : Take highest EF.
Our case we have EF 15 is highest for activity H.
The formula for LS(Late start) is
Late Start (LS) = Late Finish – Activity Duration
Activity c has 2 successor activity,take lowest one.
Step 4 : Float calculation