The document discusses the forward and backward pass technique used to find the critical path in a project schedule network diagram. The forward pass is used to determine the early start and finish times by calculating the early finish as the early start plus duration minus one. The backward pass then calculates the late start and finish times by setting the late finish to be the highest early finish and calculating late start as late finish minus duration plus one. Float is defined as the difference between late start and early start, and the critical path is the path with zero float.

1. Project Management
Key Concepts

2. CPM:
The Forward and Backward Pass

3. Forward and Backward Pass
Activity 2
Activity 1 Activity 4
Activity 3
Schedule network diagram:
Early start Duration Early finish
Activity Name
Late start Float Late finish

4. What is it?
When finding the critical path on our schedule
network diagram, we first need the early start and
finish times (via the forward pass), and then the late
start and finish times (via the backward pass).
Float is the difference between “Late Start” and
“Early Start”, and the critical path is the path that has
zero float.
Forward and Backward Pass

5. Forward and Backward Pass
5
Activity 2
5
Activity 1
15
Activity 4
10
Activity 3
1. Enter Durations
Early
start
Duration
Early
finish
Activity Name
Late
start
Float
Late
finish

6. Forward and Backward Pass
6 5 10
Activity 2
1 5 5
Activity 1
16 15 30
Activity 4
6 10 15
Activity 3
2. Perform the Forward Pass
Early
start
Duration
Early
finish
Activity Name
Late
start
Float
Late
finish
• Early start and Early finish times
• EF = ES + Duration – 1
• ES = (highest) previous EF + 1

7. Forward and Backward Pass
6 5 10
Activity 2
11 15
1 5 5
Activity 1
1 5
16 15 30
Activity 4
16 30
6 10 15
Activity 3
6 15
3. Perform the Backward Pass
Early
start
Duration
Early
finish
Activity Name
Late
start
Float
Late
finish
• Late start and Late finish times
• Enter highest EF in last box
• LS = LF – Duration + 1
• LF = (lower) LS – 1

8. Forward and Backward Pass
6 5 10
Activity 2
11 5 15
1 5 5
Activity 1
1 0 5
16 15 30
Activity 4
16 0 30
6 10 15
Activity 3
6 0 15
4. Calculate Float
Early
start
Duration
Early
finish
Activity Name
Late
start
Float
Late
finish
• Late start – Early Start