Critical path method (cpm)
- 1. Critical Path Method (CPM)
- 2. CPM is a network diagramming technique used to predict total project duration. CPM is an analysis technique with three main purposes: To calculate the project’s finish date To indentify to what extent each activity in the schedule can slip(float) without delaying the project To identify the activities with highest risk that cannot slip without changing the project finish date2
- 3. CPM How does the Critical Path Method calculate the project’s finish date? o Forward pass calculation calculates Early Start and Early Finish dates o Backward pass calculation calculates Late Start and Late Finish dates 3
- 4. Early Start (ES) is the earliest date a task can start Early Finish (EF) is the earliest date a task can be completed Late Start (LS) is the latest date a task can start without delaying the project and date Late Finish (LF) is the latest date a task can finish without delaying the project end date 4
- 5. 5 Start D 5 F 2 C 6 Finish E 4 B 1 A 2 Forward Pass 0 0 0 1511652 550 1515 1111 13
- 6. • Early Start (ES) = Latest related early date of all immediate predecessors ES= immediate Predecessors’ ES max Early finish (EF) = Early Start + Duration EF= ES + D 6 Activity A ES EF ES=3 ES=9 ES=10 D
- 8. Late Finish (LF) = Earliest related late date of all immediate successors LF= immediate Successors’ LF min Late Start (LS) = Late Finish – Duration LS= LF-D 8 Activity A LS LF LF=3 LF=9 LF=10D
- 9. The purpose of backward pass is to find the float. Float is the amount of time an activity can be delayed or lengthened. Also called slack. Total float: the amount of time an activity can be delayed or extended without extending the overall project’s completion time 9
- 10. What is the total Float for activity A? 10 Start D 5 F 2 C 6 Finish E 4 A 2 0 0 0 0 0 108 50 15 15 11 1165 1110 2 550 115 1515 1515 1111 13 B 1 1513
- 11. 11 Total float = LF-ES-D A 2 0 108 65 1110 2 B 1 LFLSEFES 10820 A A Float Float
- 12. Total Float: TF= LF - ES – D TF= LF – (ES+D) = LF-EF TF= LF-D-ES= LS-ES 12 Activity A LS LF ES EF
- 13. Free Float: the amount of time an activity can be delayed without delaying the early start date of its subsequent tasks 13 Activity A LS LF ES EF
- 14. What is the FF for activity A? What would happen if A uses its max float? (A)EF=LF=10 (B) ES=LS=10 IF the early finish date of activity A =5 the early start date of activity B=5 FF=5-2=3 14 A 2 0 108 65 1110 2 B 1
- 15. Free Float: the amount of time an activity can be delayed without delaying the early start date of its subsequent tasks EF= ES(B) – EF(A) EF= ES(earliest successor)- EF 15 Activity A LS LF ES EF
- 16. Why floats are important in the critical path method? If an activity has a TF=0, what does this mean? Floats determine thee criticality of an activity Critical activities have the least amount of Float Floats determine the critical path 16
- 17. The critical path is made of activities that cannot be delayed without delaying the final date of the project If an item is on critical path, it has a zero float The critical path is the path with longest duration It is possible to have more than one critical path 17
- 18. What is the critical path? What is the length of the critical path? 18 Start D 5 F 2 C 6 Finish E 4 A 2 0 0 0 0 0 108 50 15 15 11 1165 1110 2 550 115 1515 1515 1111 13 B 1 1513
- 19. Critical Path Method (CPM) CPM is a network diagramming technique used to predict total project duration A critical path for a project is the series of activities that determines the earliest time by which the project can be completed The critical path is the longest path through the network diagram and has the least amount of slack or float Slack or float is the amount of time an activity may be delayed without delaying a succeeding activity or the project finish date 19
- 20. Calculating the Critical Path First develop a good network diagram Add the duration estimates for all activities on each path through the network diagram The longest path is the critical path If one or more of the activities on the critical path takes longer than planned, the whole project schedule will slip unless the project manager takes corrective action 20