The presentation is part of Ace the PMP Exam, available on the iBookstore. Go to http://Aceitguides.com for more information. The critical path is the longest path in a network diagram, and therefore determines the shortest time that it will take to complete a project. This systematic way of determining the critical path uses the techniques of forward pass and backward pass. For a simple way of determining the critical path, useful for quickly answering some questions on the PMP® exam, see A Simple Method of Determining the Critical Path video in this series.

1. The Critical
Path Method
This presentation is part of
Ace the PMP Exam

2. A systematic method for determining the
critical path
The critical path is the longest path in a network
diagram, and therefore determines the shortest time
that it will take to complete a project.
This systematic way of determining the critical path
uses the techniques of forward pass and backward
pass.

3. A systematic method for determining the
critical path
You use a forward pass to calculate the Early Start and Early Finish times and a
backward pass to calculate the Late Start and Late Finish times, and therefore
calculate the float. Let’s look at what these mean.
•Early Start — the earliest time that the activity can logically start
•Early Finish — the earliest time that the activity can logically finish
•Late Start — the latest time the activity can logically start without delaying
the project or a milestone
•Late Finish — the latest time the activity can logically finish without delaying
the project or a milestone
•Float — the amount of time an activity can be delayed without affecting the
project schedule

4. The Forward Pass
Touch the screen to continue

5. We will use the forward pass to determine the Early
Start and Early Finish values of all the activities.
A D F
2 3 3
The Forward Pass
B
0
0
8
Start E End
2
C
4
Touch the screen to continue

6. The Early Start is the value The Early Finish is the
We will use the
from the Start Milestone forward passplus the
Early Start to determine the Early
Start and Early Finish values of all the activities.
duration of the activity
0 2
A D F
2 3 3
B
0
0
8
Start E End
2
C
4 Activity A
Touch the screen to continue

7. The Early Start is the value The Early Finish is the
from the Start Milestone Early Start plus the
duration of the activity
0 2
A D F
2 3 3
The Early Start is the
value from the Start The Early Finish is the
Milestone Early Start plus the
0 8
B duration of the activity
0
0
8
Start E End
2
C
4 Activity A
B
Touch the screen to continue

8. Activity C
0 2
A D F
2 3 3
The Early Start is the
value from the Start The Early Finish is the
Milestone Early Start plus the
0 8
B duration of the activity
0
0
8
Start E End
2
The Early Start is the 0 4
value from the Start
C
The Early Finish is the
Milestone 4 Activity B
Early Start plus the
duration of the activity
Touch the screen to continue

9. The Early Start is the The Early Finish is the
Early Finish value from Early Start plus the
Activity A Activity C
duration of the activity
0 2 2 5
A D F
2 3 3
0 8
B
0
0
8
Start E End
2
The Early Start is the 0 4
value from the Start
C
The Early Finish is the
Milestone 4 Activity D
Early Start plus the
duration of the activity
Touch the screen to continue

10. The Early Start is the The Early Finish is the
Early Finish value from Early Start plus the
Activity A duration of the activity
0 2 2
A D 5 F
2 3 Early Start is the
The 3
Early Finish value from
Activity B
✓ (not Activity C) as this The Early Finish is the Early
Start plus the duration of
0 8 is the later Early Finish
B time. the activity
0
0
8
8 10
Start E End
✗ 2
0 4
C
4 Activity D
E
Touch the screen to continue

11. The Early Start is the Early Finish value The Early Finish is the Early
from Activity B (not Activity D) as Start plus the duration of
this is the later Early Finish time. the activity
✗
0 2 2
A D 5 8 F 11
2 3 Early Start is the
The 3
Early Finish value from
Activity B
✓ (not Activity C) as this The Early Finish is the Early
Start plus the duration of
0 8 is the later Early Finish
B time. the activity
0
0
8
8 10
Start E End
✗ 2
0 4
C
4 Activity F
E
Touch the screen to continue

12. The Early Start is the Early Finish value The Early Finish is Early
The value for the End milestone is the the Early
from Activity B FinishActivity D)Activity F (not Activity E) as
(not value from as Start plus the duration of
this is the later Early Finish is the later Early Finish time.
this time. the activity
✗ ✓
0 2 2 5 8 11
A D F
2 3 3
✓
0 8
B
0
0 11
11
8
✗
8 10
Start E End
2
0 4
C
4 End Milestone
Activity F
Touch the screen to continue

13. The value for the End milestone is the Early
That completes Finishforward pass F (not Activity E) as
the value from Activity
this is the later Early Finish time.
✓
0 2 2 5 8 11
A D F
2 3 3
0 8
B
0
0 11
11
8
✗
8 10
Start E End
2
0 4
C
4 End Milestone
Touch the screen to continue
End

14. The Backward Pass
Touch the screen to continue

15. We will use the backward pass to determine the Late
Start and Late Finish values of all the activities.
0 2 2 5 8 11
A D F
2 3 8 3 11
The Backward Pass
0 8
B
0
0 11
11
8
8 10
Start E End
2
0 4
C
4
Touch the screen to continue

16. The Late Start is the Late Finish minus The Late Finish is the value
We will usethe duration of the activity to
the backward pass determinethe End Milestone
from the Late
Start and Late Finish values of all the activities.
0 2 2 5 8 11
A D F
2 3 8 3 11
0 B 8 Activity F
0
0 11
11
8
8 10
Start E End
2
0 4
C
4
Touch the screen to continue

17. The Late Start is the Late Finish minus The Late Finish is the value
the duration of the activity from the End Milestone
0 2 2 5 8 11
A D F
2 3 8 3 11
0 B 8 Activity E
F
0
0 11
11
8
8 10
Start E End
The Late Start is the Late 9 2 11 The Late Finish is
0 C 4
Finish minus the duration of the value from the
the activity End Milestone
4
Touch the screen to continue

18. The Late Start is the Late Finish minus The Late Finish is the Late
the duration of the activity Start value from Activity F
0 2 2 5 8 11
A D F
2 5 3 8 8 3 11
0 B 8 Activity D
E
0
0 11
11
8
8 10
Start E End
The Late Start is the Late 9 2 11 The Late Finish is
0 C 4
Finish minus the duration of the value from the
the activity End Milestone
4
Touch the screen to continue

19. The Late Start is the Late Finish minus The Late Finish is the Late
the duration of the activity Start value from Activity F
0 2 2 5 8 11
A D F
2 5 3 8 8 3 11
0 B 8 Activity C
D
0
0 11
11
8
8 10
Start E End
9 2 11
The Late Start is the
0 4
Late Finish minus the C The Late Finish is the Late Start
duration of the activity 5 4 9 value from Activity E
Touch the screen to continue

20. 0
✓
A 2 2 D 5 8 F 11
2
The Late Start is the Late 5 3 8 8 3 11
Finish minus the duration
of the activity
The Late Finish is the Late Start value
0 B 8 Activity C
from Activity F (not Activity E) as
0
0 11
this is the earlier Late Start time.
11
✗
0 8 8
8 10
Start E End
9 2 11
The Late Start is the
0 4
Late Finish minus the C The Late Finish is the Late Start
duration of the activity 5 4 9 Activity B
value from Activity E
Touch the screen to continue

21. The Late Start is the Late The Late Finish is the
Finish minus the duration Late Start value from
of the activity Activity D
0
✓
A 2 2 D 5 8 F 11
2 5
The Late3Start is the Late 5 3 8 8 3 11
Finish minus the duration
of the activity
The Late Finish is the Late Start value
0 B 8 from Activity F (not Activity E) as
0
0 11
this is the earlier Late Start time.
11
✗
0 8 8
8 10
Start E End
9 2 11
0 4
C
5 4 9 Activity A
B
Touch the screen to continue

22. The Late Start is the Late The Late Finish is the backward
That completes the pass
Finish minus the duration Late Start value from
of the activity Activity D
0 2 2 5 8 11
A D F
3 2 5 5 3 8 8 3 11
0 8
B
0
0 11
11
0 8 8
8 10
Start E End
9 2 11
0 4
C
5 4 9 Activity A
Touch the screen to continue
End

23. Calculating float
If an activity can be delayed it is said to have float (or
slack). To calculate float you subtract the Early Start
from the Late Start (or the Early Finish from the Late
Finish, it amounts to the same thing).
The amount of float is indicated as a number above the
box.

24. Calculating float
Here is the network diagram with the float indicated
above each activity
3 3 0
0 2 2 5 8 11
A D F
3 2 5 5 3 8 8 3 11
0
0 8
B
0
0 11
11
0 8 8 1
8 10
Start E End
5 9 2 11
0 4
C
5 4 9

25. The Critical Path
The critical path is the path through the activities that
have no float, in this case activities B and F.
3 3 0
0 2 2 5 8 11
A D F
3 2 5 5 3 8 8 3 11
0
0 8
B
0
0 11
11
0 8 8 1
8 10
Start E End
5 9 2 11
0 4
C
5 4 9

26. A systematic method for determining the
critical path
That was a systematic method of determining the
critical path in a network diagram using the forward
pass and the backward pass.
For a simple way of determining the critical path, useful
for quickly answering some questions on the PMP®
exam, see A Simple Method of Determining the
Critical Path video in this series.

27. The Critical
Path Method
This presentation is part of
Ace the PMP Exam