Module 13: Develop Schedule, Critical Path Method
#outcomes
Learning Outcomes
As a Project Manager, this is the stage in which you create a schedule model as the network diagram
and the activity duration estimates are finished. Develop Schedule involves the correlation between
activities, dependencies, LEADS and LAGS, and estimation. The resulting schedule, represented in a
visual presentation, creates the baseline for the project and is an output to this process. The Develop
Schedule process is iterative and occurs at several times during the life cycle of the project.
At the completion of this module, you will be able to:
 Use PDM networks to sequence and calculate the project’s length of time
 Use Critical Path Method to calculate the length of the project and the float of activities
 Explain the importance of activities on Critical Path
 Explain the difference between Free Float and Total Float
/outcomes
Required Readings
Chapter 5, 6, 9
Activities to supplement/support learning
PMBOK® Guide Chapter 6
Develop Schedule – Inputs
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Schedule Management Plan – outlines the scheduling method and tools used to calculate the
schedule
Activity List – details the activities to be included in the schedule model
Activity Attributes – provides details used to develop schedule
Project Schedule Network Diagrams – reveals the logical relationship of predecessors and
successors used in the schedule
Activity Resource Requirements – identifies the types and quantities of resources
Resource Calendars – determines the availability of resources
Activity Duration Estimates – assessments of the number of work periods required to complete
the activities required
Project Scope Statement
o Assumptions - for schedule development purposes are considered to be true, real, or
certain
o Constraints – limit options e.g. imposed dates, or key events, milestones set by Sponsor
Risk Register – identification of all project risks and the impact to the schedule
Project Staff Assignments – describes which resources are assigned to each activity
Resource Breakdown Structure
Enterprise Environmental Factors
o Standards
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o Communication Channels
o Scheduling tools
Organizational Process Assets
Develop Schedule – Tools and Techniques
PDM (Precedence Diagramming Method) Networks
A special type of AON is the PDM network (a network that can allow you to calculate the Critical Path;
and find the duration of the project) and it is used extensively in Project Management.
Precedence Diagramming Method
 Also referred to as Activity-on-Node (AON)
 Work is done at the “Node”
 Dependency relationship illustrated by arrow
 Is a schematic display of project activities
 Illustrates the interdependence of all tasks and work packages
 Facilitates communication flow because it shows the interrelationship among activities and
project personnel
Why use Precedence Diagramming Method?
 Helps with resource planning
 Creates a baseline for critical activities
 Determines when the project will end (the duration)
 Shows dependencies among activities
Network Diagram Calculation
To get further clarity on Network Diagram Calculations, you can view the following video:
https://www.youtube.com/watch?v=VYUPWwJhUgM
Once the Project Manager has determined the logical sequence of activities in a project, the duration of
the project duration can be calculated. Using network diagram calculation, you will notice that there
may be many paths originating from one point and ending at another point. Every path will have a
duration attached, and the path with the longest duration is known as the Critical Path.
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Critical Path is the sequence of events that if any are delayed, will delay the entire project. This
path also is the sequence of tasks that will take the longest to complete to deliver the project.
The following diagram shows the legend that will be used in the calculation of project duration:
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Using the legend above, you will note that there are 5 activities to meet the project deliverable(s). Each
activity is assigned a duration (5, 6, 3, 4, 2 days).
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Forward Pass
The first calculation necessary for determining the duration of a project is called the Forward Pass.
Forward Pass is a calculation starting with the first activity and culminating with the last activity
performed to fin the early dates and the duration of a specific project.
#note
When calculating forward pass, if there is a merge relationship, the largest number is brought forward
(see end activity – 11)
/note
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EF = ES + Duration
ES = Max EF of related predecessor
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Backward Pass
In order to determine the float of a project, and subsequent Critical Path, use the Backward Pass
calculation. Backward pass is a scheduling calculation done to determine the activity late dates. This
calculation begins with the last activity and project duration and culminates with the first activity.
#note
When calculating backward pass, the smallest number is brought backwards.
/note
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LS = LF – Duration
LF = Min LS of related successor
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The float is calculated by demining the difference between either:
 EF and LF, or
 EX and LS
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#key point
Critical Path
/key point
Float
Float is the number of days that an event or lag can be delayed or extended without impacting the
completion of the project.
Free Float
Free Float is the amount of time that a schedule activity can be delayed without delaying the early start
date of any successor or violating a schedule constraint.
#note
Float is sometimes referred to as slack or slide time.
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Total Float
Total Float is the amount of time that as schedule activity can be delayed or extended from its early start
date without delaying the project finish date or violating a schedule constraint.
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PDM Network Practice
#activity
PDM Network Example 1
Look at the following PDM and calculate the Forward Pass.
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/reveal
Now calculate the Backward Pass.
#reveal
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/reveal
And finally calculate the Float and the Critical Path.
#reveal
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/reveal
PDM Network Example 2
Look at the following PDM and calculate the Forward Pass. REMEMBER: when there are burst or merge
activities the largest duration is brought forward.
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#reveal
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/reveal
Now calculate the Backward Pass.
#reveal
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/reveal
And finally calculate the Float and the Critical Path:
#reveal
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/reveal
PDM Network Example 3
Look at the following PDM and calculate the Forward Pass. REMEMBER: when there are burst or merge
activities the largest duration is brought forward.
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#reveal
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/reveal
Now calculate the Backward Pass on Example 3. REMEMBER: When calculating backward pass, the
smallest number is brought backwards
How did you do?
#reveal
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/reveal
And finally calculate the Float and the Critical Path:
#reveal
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The Total Float is the amount of time an activity can be delayed without delaying the project end date
or an intermediary milestone is calculated as follows. Note that the Critical Path activities are: B,E,D,G
as they all have a float of zero.
/reveal
Test Your Understanding
Do the Forward Pass and Backward Pass and then determine the Critical Path on the following example:
#reveal
The project duration is 14 days and the Critical Path actitivities are: A, B, D, and E. How did you do?
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/reveal
Key Terminology
Forward Pass - A calculation starting with the first activity and culminating with the last activity
performed to find the early dates and the duration of a specific project.
Backward Pass - A scheduling calculation done to determine the activity late dates. This calculation
begins with the last activity and project duration and culminates with the first activity.
Float - The number of days that an event or lag can be delayed or extended without impacting the
completion of the project.
Early Start (ES) - The earliest that an activity can start.
Early Finish (EF) - The earliest that an activity can possibly finish.
Late start (LS) - The latest that an activity can start and not impact project completion.
Late Finish (LF) - The latest that an activity can be completed without impacting the project completion.
Critical Path- is the longest continuous chain of activities through the network schedule that establishes
the minimum overall project duration. Project managers should apply extra monitoring and control
activities on activities on Critical Path as any delay on them will impact the length of the project. In the
following modules you will learn about strategies to deal with such scenarios.
Develop Schedule – Outputs
As a minimum, the project schedule should include project start and project finish dates for each
activity. Often graphically presented, 3 common forms:
1. Bar Charts
2. Milestone Charts
3. Project Schedule Network diagrams
Often the Baseline is shown in the same graph: each task bar is split in top (current/actual) and bottom
half (baseline).
The outputs of Develop Schedule are as follows:
 Schedule Baseline
 Project Schedule
o Bar Charts
o Milestone Chart - reflects status of events over time. Advantages/disadvantages similar
to Gantt chart
The following is an illustration of a Milestone Chart:
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 Project Schedule Network Diagrams
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 Bar Chart (aka Summary Schedule)
o Reflect status of activities over time
o Depict schedule and progress against plan
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Schedule Data
o Milestones, activities, attributes
o Assumptions and constraints
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o Could include alternative schedules, contingency reserve
o Resource Histograms, Cash-flow projections, Order & Delivery Schedules
Project Calendars
Project Management Plan Updates
Project Documents Updates
o Activity Resource Requirements
o Activity Attributes
o Calendar
o Risk Register
#assignment
Assignment #9
Using the following information:
1. Calculate the forward pass
2. Calculate the backward pass
3. Determine the length of the project
4. Identify the activities on the Critical Path
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/assignment
Summary
This module focused on the use of PDM networks to determine the Critical Path and the float of each
activity. Using Critical Path, you were able to find the longest path in the network and from there the
length of the project. The calculation behind finding Critical Path is crucial to learning scheduling
concept of the project as it applies to all projects and all scheduling software in the market.
If you find you have any questions about any of this, pose your question on the “Questions about Course
Content” discussion forum. Read the forum regularly; you may be able to answer someone else’s
question. Your instructor will also watch the forum and answer your questions there so everyone can
see the response.