5th Edition PMBOK® Guide—Chapter 6: Process 6.7 Control Schedule

In controlling a project, you must be able to control the constraints of that project, and the time constraint, i.e., the schedule, is an example of that. In the process 6.7 Control Schedule, you have the only process under Schedule Management in the Monitoring & Controlling process group, the rest (6.1 through 6.6) being in the Planning process group.

The purpose of this post is to do a quick overview of the inputs, tools & techniques, and outputs of this process.

1. Inputs

The inputs come from the schedule model (the output of process 6.6 Develop Schedule), but also from the work performance data which are an output of the Integration Management process 4.3 Direct and Manage Project Work.

2. Tools & Techniques

The technique of “performance reviews” actually encompasses some techniques which were also used to create the schedule model, such as the critical path method, the critical chain method. Most crucial for the monitoring and controlling process, however, is earned value management, which tells you how well your project is progressing as compared to the schedule and cost baselines.

Many of the other techniques (resource optimization, schedule compression, etc.) that were used in the creation of the schedule model in the planning process group, can also be used in the monitoring and controlling process group to control the schedule.

3. Outputs

The most crucial outputs are the work performance information in the form of schedule variance (SV) and schedule performance index (SPI). These can be used to forecast future performance of the project based on the performance to date. If this information indicates that there is a significant variance of the performance of the project as compared to the performance baseline, then this may suggest changes to either the project itself in the form of corrective action or preventive action, or changes to the schedule baseline itself if it is determined that the original baseline was unrealistic.

Any of these change requests are then fed as inputs into the change control process, which as you may recall takes place under Integration Management. If there is an eventual change to the schedule baseline, then that will generate a new project schedule. If schedule compression techniques are used, this may create changes in other management areas: cost (in the case of crashing) and risk (in the case of fast-tracking).

Finally, if the reason for the variances is uncovered, this is noted in the lessons learned so that further scrutiny can be given to this throughout the rest of the project.

1. Project Management Plan The two specific elements of this overall plan that are used as inputs are

  • Schedule Management Plan—describes how the schedule will be managed and controlled. It is an output of process 6.1 Plan Schedule Management.
  • Schedule Baseline—used as a reference to compare with the actual results to determine if corrective action, preventive action, or even a change to the baseline itself required. It is an output of process 6.6 Develop Schedule.
2. Project Schedule The project schedule refers to the output of the schedule model. The most recent version of that schedule is used as an input to indicate activities started, activities completed, and any updates to activity start or end dates as of the indicated date. It is an output of process 6.6 Develop Schedule.
3. Work Performance Data Information about project progress such as which activities have been started and the extent of their progress, and which activities have been completed. It is an output of process 4.3 Direct and Manage Project Work from Integration Management.
4. Project Calendars The schedule model may require some activities to be scheduled in different work periods, which may be contained in different project calendars. These are an output of process 6.6 Develop Schedule.
5. Schedule data The schedule model consists of the schedule data (the input) and the project schedule (the output). The schedule data, an output of process 6.6 Develop Schedule, is reviewed and possibly updated as part of the upcoming process.
6. OPAs
  • Policies, procedures, and guidelines for scheduling.
  • Schedule control tools
  • Monitoring and reporting methods
1. Performance reviews Measures, analyzes and compares schedule performance based on data such as actual start and finish dates, percent complete, and remaining duration of work. Techniques used may include:

  • Trend analysis
  • Critical path method
  • Critical chain method
  • Earned value measurement
2. Project Management Software This is a tool (Microsoft Project, Primavera, etc.) which can:

  • Track planned vs. actual dates
  • Report variances from the schedule baseline
  • Forecast the effect of changes on the schedule model
3. Resource optimization techniques Used to adjust schedule due to demand (project time) and supply of resources (resource availability).

  • Resource leveling
  • Resource smoothing
4. Modeling techniques Used to review various scenarios used in risk monitoring to bring schedule model in alignment with project management plan and schedule baseline.

  • What-if scenario analysis: used to assess feasibility of the project schedule under adverse conditions
  • Simulation: calculates multiple project durations based on different sets of assumptions (Monte Carlo analysis)
5. Leads and lags Used to bring project activities that are behind into alignment with the plan.
6. Schedule compression Used to bring project activities that are behind into alignment with the plan.

  • Crashing: adds resources
  • Fast-tracking: activities normally done in sequence are now performed in parallel for part of their duration
8. Scheduling tool Automated scheduling tools contain the schedule model by allowing one to input the scheduling data and to monitor the schedule via the output (the project schedule).
1. Work Performance Information The schedule variance (SV) or schedule performance index (SPI) calculated for the work packages and control accounts of the WBS.
2. Schedule Forecasts Estimates of the future conditions of the project based on the work performance information provided.
3. Change Requests Performance reviews, including schedule variance analysis, may result in change requests to the schedule baseline. These are then input to the Perform Integrated Change Control process 4.5 in Integration Management.
4. Project Management Plan Updates
  • Schedule baseline
  • Schedule management plan
  • Cost baseline: schedule compression technique of crashing may require additional resources
6. Project Documents Updates
  • Schedule data: if a new schedule is generated, more realistic schedule data may result
  • Project schedule: updated schedule data will result in a schedule model which generates an updated project schedule
  • Risk register: schedule compression technique of fast-tracking may generate new risks
7. OPAs
  • Causes of variances
  • Corrective action (if chosen)
  • Lessons learned from schedule control

The next series of posts will cover the tools and techniques of this process, starting with the first technique of performance reviews. As you can see from the chart, this encompasses four separate techniques, all of which will be discussed in the next post.

5th Edition PMBOK® Guide—Chapter 6: Schedule Compression Techniques

1. Introduction

What if you want to shorten the schedule of your project without having to change the scope? To do so, you can use one of the schedule compression techniques, which change one of the other project constraints, either cost or risk.

Technique Description Increases
1. Crashing Shortens schedule by adding resources to activities Cost
2. Fast-Tracking Activities done in sequence are now performed in parallel Risk

The thing to remember about each of these techniques is that they are done on critical path activities. If they were done on non-critical path activities, it would reduce the duration of those activities, but would not necessarily reduce the duration of the project itself.

Crashing is done by adding resources to a group of activities for the least amount of additional cost required to shorten the duration of those activities by the given amount. Having people work overtime, or hiring additional workers on a temporary basis to do an activity are examples of crashing a project.

Fast tracking is done by taking activities that are in sequence and putting them in parallel to a certain extent. This increases the risk because two activities are going on once for at least part of the work.

2. Crashing exam question example

Given the chart below, what is the cost of completing the project so that it only takes 7 days to complete?

Task Duration Predecessor Cost Crash Cost Maximum
Crash Days


None 1500 300/day 1


A 1000 200/day 2


A 2400 300/day 2


B 1100 100/day 1


C 500 100/day 1

Step 1: Figure out the critical path.

If you draw the network, the possible paths through the network from start to finish are A-B-D = 3+ 5 + 3 = 11 days or A-C-E = 3 + 4 + 2 = 9 days.

Step 2: Figure out the various possible options you have of different combinations of activities to crash in order to achieve the given result.

Therefore A-B-D is the critical path and A, B, and D are the activities you must concentrate on therefore to reduce to 7 days. However, if the critical path A-B-D is reduced by 4 days, then the durations of the paths will be A-B-D = 7 days and A-C-E will be 9 days, and it will become the new critical path. In order to shorten A-C-E from 9 days to 7 days, you will also have to reduce its duration by 2 days as well.

With the pathway A-B-D, you can shorten A by 1, B by 2, and D by 1 for a total of 4 days. With A-C-E, since you have already shortened A, you must either shorten a combination of C or E by 2 days in order to reduce it by 2 days. Since C can be shortened by 2, and E by 1, there are two ways of doing this:

Option 1: Shorten C by 2 days

Option 2: Shorten C by 1 day, and E by 1.

Step 3: Compare the costs of the different options.

Task Duration Predecessor Cost Crash Cost Maximum
Crash Days
Option 2


None 1500 300/day 1 300 300


A 1000 200/day 2 400 400


A 2400 300/day 2 600 300


B 1100 100/day 1 100 100


C 500 100/day 1 100
Subtotal 6500 1400 1200
Total 7900 7700

The cost of accomplishing the activities A through E without crashing are 6500. With crash option 1, you are adding 1400 of cost, and with crash option 2, you are adding 1200 of cost. Since 1200 is the option with the least amount of additional cost, you should choose this for a total of 6500 + 1200 = 7700.

Note: be carefu; of the wording of these questions. Some questions will ask you how much it will cost to crash the project, meaning what is the cost of reducing the duration of the project. Other questions, like this one, will ask about the total cost of the project, which will equal the regular cost plus the cost to crash the project.

This is the last of the tools & techniques, except for the project management information software (Microsoft Project, Primavera, etc.). The next post will discuss the last of the schedule management processes, this one being the process used to monitor and control the schedule.

5th Edition PMBOK® Guide—Chapter 6: Leads and Lags

One technique for adjusting the schedule module by reducing the duration of certain activities is adjust their leads and/or lags. This post will review what leads and lags are, describe the technique, and give a typical exam question involving leads and lags.

1. Leads and lags–definition


Leads The amount of time whereby a successor activity can be advanced with respect to a predecessor activity.
Lags The amount of time whereby a successor activity is required to be delayed with respect to a predecessor activity.

2. Leads and lags as scheduling technique

If there is a given lead or lag for an activity, it can be seen that increasing the lead of the successor activity will reduce the total duration of the two activities. Likewise, decreasing the lag of the successor activity will also reduce the total activity of the two activities. However, looking at the definitions above, and given that the lag is usually a requirement, and a lead is the amount of time that a successor activity can be advanced, it is more likely that you will be able to increase a lead rather than decrease a lag.

3. Typical exam question using leads and lags.

Activity 1 has a duration of 20 days, Activity 2 of 10 days, Activity 3 of 5 days and Activity 4 of 6 days. The relationship between activity 1 and activity 2 is FS, between activity 2 and activity 3 is FF-2 (2-day lead), and between activity 3 and 4 is FS+3 (3-day lag). What is the minimum total duration between the Milestones A and B?

  1. 36 days
  1. 37 days
  2. 39 days
  3. 42 days

This is an example of a question showing LEADS and LAGS.  You have to know the four dependencies, which are

FS  = successor activity cannot start until predecessor activity is finished 

FF  = successor activity cannot finish until predecessor activity is finished

SS = successor activity cannot start until predecessor activity has started

SF = successor activity cannot finish until predecessor activity has started

 In each of these four combinations, the first letter represents the PREDECESSOR activity, and the second letter represents the SUCCESSOR activity.   That’s a good way to remember that the PREDECESSOR activity is the one that comes first before the SUCCESSOR activity.   

FS is the most common relationship and it shows that the activities are done in SERIES, one after the other.
FF and SS are the next most common relationships and they show that the activity are done in PARALLEL (i.e., at the same time). SF is rarely used and you will not most likely not see it on the exam.

So with that background, here’s how you figure out the question.

Step 1: Activity 1 starts at 0 and ends at 20 days (you are given the duration of 20 days in the question).   When does Activity 2 start?   Well, the FS means that Activity 2 (the successor activity) starts IMMEDIATELY after Activity 1 is finished, so it starts on day 20 as well.   

Activity Starts Ends
Activity 1 0 20
Activity 2 20
Activity 3
Activity 4

 Step 2:

Activity 2 starts at 20 and ends at 30 days (you are given the duration of 10 days in the question).   When does Activity 3 start?    Well, you are given FF, so you can’t figure out directly when it starts like you could for Activity 2 which used FS.   Since you are given FF, it means you can figure out when it FINISHES.   FF – 2 days means that Activity 3 finishes 2 days BEFORE Activity 2 finishes.   Since Activity 2 finishes on day 30 (see beginning of paragraph for reference), Activity 3 finishes on day 30 – 2 = 28.  

Activity Starts Ends
Activity 1 0 20
Activity 2 20 30
Activity 3 28
Activity 4

 Step 3:

When does Activity 4 begin?   According to the chart, it starts on FS + 3 days, meaning that it starts 3 days AFTER activity 3 ends.   Since activity 3 ends on day 28, activity 4 begins on day 28 + 3 = 31.   When does activity 4 end?   Since the duration is given as 6 days, the answer is 31 + 6 = 37 and the answer is therefore B.

Although not required for the answer, I have filled in the activity 3 starting date of day 23 because it ends on day 28, and has 5 days duration, meaning the start is on day 28 – 5 = 23.

Activity Starts Ends
Activity 1 0 20
Activity 2 20 30
Activity 3 23 28
Activity 4 31 37

This shows you how to use the knowledge of leads and lags to answer a typical exam question. The next post deals with the two methods of schedule compression: fast-tracking and crashing.

5th Edition PMBOK® Guide—Chapter 6: Modeling Techniques

This post covers Modeling Techniques, one of the types of tools & techniques used in the final planning process under Schedule Management, process 6.6 Develop Schedule.

1. What-If Scenario

The purpose of the technique is to refine the schedule model by accounting for the effect of various risks or scenarios on the project schedule, such as: What will happen if there is a delay in the delivery of a major component?

The idea is that the effect on the project schedule of various scenarios or risks are assessed. How vulnerable is the schedule to these adverse conditions? Can contingencies or response plans be prepared to reduce the impact to the schedule of these various adverse conditions? Contingency reserves that pay for these contingencies or response plans may be needed to be added to the project estimate to get the cost baseline.

If the scenario is tied to a certain activity or stage of the project, and that scenario does not occur, then the contingency reserves tied to that scenario may be deemed no longer necessary, and can be used to reduce the cost baseline. Also, the potential negative impact on the schedule may be deemed no longer necessary, which can be used to reduce the range for the duration of that particular activity.

This shows that, as the risk on a project gets reduced throughout a project, this also reduces the uncertainty in both the budget and the schedule.

2. Simulation (Monte-Carlo Analysis)

A three-point estimate gives a range of durations for each activity, the tP or pessimistic estimate, the tO or optimistic estimate, and the tM or most likely estimate. What happens when you get a large number of activities, each with their own set of three estimates for the activity durations? How do you determine the likely duration of the project of the whole?

One way is through simulation, which takes the various activities and performs a calculation simulating various possible outcomes for each activity, and then based on this simulation of the individual activities, calculates the possible outcome for the overall project. The most common form of simulation of this type is Monte Carlo analysis. When you are doing a problem in the form of Estimated Monetary Value in risk management, you are doing a very simple form of this simulation using only two scenarios. If you can imagine extending this type of calculation for scenarios involving hundreds or more activities, you can get an idea of what the Monte Carlo analysis does and why it takes a computer to figure it out.

3. Conclusion

These modeling techniques offer a layer of refinement to the estimate of the duration of the schedule by showing the affect of risk. This is important because it not only makes the schedule more robust, i.e., able to be executed under adverse conditions, but can also become a tool in managing the risk on the project as well as its schedule.

The next tool and technique to be reviewed is that of leads and lags. Unlike modeling techniques, leads and lags are a tool that lends itself to questions involving calculation on the exam.

5th Edition PMBOK® Guide—Chapter 6: Resource Optimization Techniques

The duration of a project activity will depend on the availability of resources you can apply to that activity. That is why the process 6.4 Estimate Activity Resources comes before process 6.5 Estimate Activity Durations.

Once you get a schedule model together, you may have to adjust it depending on the supply and demand for resources not only within the project, but between projects in a company. That’s why you may need one of the following resource optimization techniques: resource leveling and resource smoothing.

1. Resource leveling

This is used when critical resources are shared between projects or are overallocated either a) to one or more activities that are concurrent within a project or b) to one or more concurrent projects within an organization.

Thus the demand for resources outstrips the supply, and resource leveling is done to make sure that the supply meets the demand. In practical terms, it often happens like this. If Resource A is assigned to an activity on project #1 for eight hours a day, and resource A is shared between two different projects, project #1 and project #2, then resource leveling would then assign resource A to project #1 for 4 hours a day, and to project #2 for 4 hours a day. Notice that, in terms of project #1, this would double the amount of days it would take to do a particular activity using Resource A.

In fact, it is worthwhile noting that because it necessarily increases activity durations, resource leveling can even have an affect on the critical path of a project.

2. Resource smoothing

This is when the requirements for resources on a project are kept within certain predefined resource limits, for example, if Resource A is only working part-time on a project, the number of hours that Resource A is assigned to the project may be limited. The difference between resource smoothing and resource leveling is that resource smoothing is only used on activities that have float, so they cannot affect the critical path of a project like resource leveling can.

I hope this post clears up the difference between resource leveling and resource smoothing because the terms sound similar, and in fact, are both used for the same general purpose, to adjust the demand for resources on a project with a given supply. The difference between them comes to the fact that resource smoothing is used only for activities that are not on the critical path, whereas resource leveling has no such restriction, and can indeed affect the critical path of a project.

The next post covers the subject of modeling techniques used to model the effect of various risks on the duration of a project.

5th Edition PMBOK® Guide–Chapter 6: Critical Chain Method


One of the tools and techniques used in the process 6.6 Develop Schedule is the critical chain method. Unfortunately, it can be easily confused with the similar-sounding critical path method, which was covered in the last two posts.

The purpose of this post is to explain briefly what the critical chain method is, how it is distinguished from the critical path method, and how the addition of buffers used in the critical chain method differ from merely padding the estimates, a practice frowned upon by PMI.

1. The Critical Chain Method

First of all, why do you need the critical chain method in the first place? In the critical path method, you are given the durations of each individual activity as definite amounts: 7 weeks, for example, to complete activity A as opposed to 5 weeks to complete activity B.

However, when you start to use three-point estimates, you realize that the duration estimates for activities are better expressed in terms of a range of durations: 5-9 weeks, for example, to complete activity A as opposed to 3-7 weeks to complete activity B.

Because the activities themselves have a range of durations, once you figure out the critical path based on, say, the most likely durations of activities, you will have a float for activities on the non-critical path which now will also have a range. There is therefore some uncertainty about the durations of the individual activities and the total duration of a non-critical path. Buffers are added to account for this uncertainty. So if an activity has a float of between 1 and 3, you would place a buffer from 1 and 3 weeks to make sure that the non-critical path feeds into the critical path at the correct time.

There are two kinds of buffers: feeding buffers for each of the non-critical paths, and then a project buffer at the end of the critical path, which the project manager can use to make sure the project finishes on time.

2. The Critical Chain Method vs. the Critical Path Method

The critical path method deals with definite durations, whereas the critical chain method is used to add buffers that account for uncertain durations (i.e., those that can be expressed as a range). It adds a level of flexibility to the critical path method, if you want to put it in those terms.

3. Buffer vs. Padding

How does adding a buffer in the critical chain method differ from simply padding an estimate? Padding an estimate means adding an arbitrary, across-the-board percentage to one’s estimates. Padding is therefore an extremely blunt instrument for making sure your project is done within the schedule. It is wasteful, in that it may add to estimates of certain activities that don’t require any such “padding.” And the arbitrariness means that there really is no basis other than guesswork in how much you add to the estimates.

With a buffer, you are adding extra built-in time to the non-critical paths of the project a) at the precise point where they are needed and b) in the precise amount which is needed. So it is a scalpel as opposed to the blunt instrument of padding, and is therefore approved by PMI, whereas padding is frowned upon by PMI.

The next post deals with the next tool and technique of this process, called resource optimization techniques. What the project requires on an optimum (8 hours a day, 5 days a week) schedule and what resources are actually available on a day-to-day basis may be two different things, and this technique reconciles the project durations to the reality of resource availability on that particular project.

5th Edition PMBOK® Guide—Chapter 6: Critical Path Method SHORTCUTS

In the last post, I discussed the formal method for determining the critical path of a network using the forward and backward pass method. This also gives you the float of each activity on the network. Recall that the float of any activity on the critical path is by definition equal to 0, the float of any activity on a non-critical path is the number of time units it can be delayed without affecting the successor activity.

There is a shortcut alternative which I found saves a lot of time, which is especially important when taking the PMP or CAPM exam.

Here’s how it works.

1. Draw the network diagram for the problem.

2. List the potential paths for the project and their durations.

3. Whichever path you find as a result of step 2 has the longest duration is the critical path.

4. Label ALL activities on the critical path as having float of 0.

5. Calculate the float of the non-critical paths found as a result of step 2 by taking the duration of the critical path minus the duration of that path.

6. Take the non-critical path with the next highest float above 0.

7. Label all activities on that non-critical path with the float of that path EXCEPT for those that you already labeled as a result of step 4.

8. Taking the non-critical path with the next highest float above the one you found as a result of step 6.

9. Label all activities on that non-critical path with the float of that path EXCEPT for those that you already labeled in a previous step.

10. Continue until all activities are labeled.

Let me illustrate.

Here is a chart with the activities of a project. Answer these questions.

1. What is the critical path of the project?

2. What is the float of each activity?

Activity Predecessor Duration Float
Start None 0
A Start 2
B A 9
C B 18
D A 6
E D 10
F A 4
G F 14
H E, G 8
I C, H 9
J I 5
End 0

If you draw the network diagram, you get the following  three paths and their durations.

Path #1: A-D-E-H-I-J , Duration = 2 + 6 + 10 + 8 + 9 + 5 = 40

Path #2: A-F-G-H-I-J, Duration = 2 + 4 + 14 + 8 + 9 + 5 = 42

Path #3: A-B-C-I-J, Duration = 2 + 9 + 18 + 9 + 5 = 43

The longest path is path #3, with duration 43. This is the critical path and all activities have a float of 0.

Let’s look at path #2, which has the next smallest duration of 43, and a float of 43 – 42 = 1. All of the activities on path #2 that are NOT ALREADY accounted for in path #3 (the critical path) are assigned a float of 1. That means F, G, H are all have float of 1.

Finally let’s look at path #1, which has the next smallest duration of 40, and a float of 43 – 40 = 3. All of the activities on path #1 that are NOT ALREADY accounted for in either path #3 or path #2 are therefore assigned a float of 3. That mean D and E have a float of 3.

So the finally answer is the duration of the critical path is 43, and the chart below contains the float of all the activities.

Activity Predecessor Duration Float
Start None 0 N.A.
A Start 2 0
B A 9 0
C B 18 0
D A 6 3
E D 10 3
F A 4 1
G F 14 1
H E, G 8 1
I C, H 9 0
J I 5 0
End 0 N.A.

If you would have done that same problem with the forward and backward pass, it would have taken a LOT longer.

The next post will cover the critical chain method; it sounds like the critical path method, but is a different technique altogether, with terminology involving “buffers” borrowed from lean manufacturing.