Time buffers are inserted where scarce resources are needed for an activity.

Critical Chain Project Management (CCPM) is a project management methodology that considers finite resources such as people, equipment, and physical space as the key project constraint. 

CCPM can be thought of as a response to the Critical Path Method — a project scheduling algorithm that effectively calculates project deadlines based on task duration, but treats every other resource as if it were infinite.

In this CCPM guide, we’ll explain:

• How Critical Chain Project Management is different from the Critical Path Method,
• How to manage projects using CCPM, and
• What are the advantages and disadvantages of CCPM.

• The difference between the Critical Chain and the Critical Path
  • What is the Critical Path?
  • What is the Critical Chain?
• How to manage projects with CCPM in 4 steps
  • Step 1: Find the Critical Path
  • Step 2: Level the resources
  • Step 3: Implement buffers
  • Step 4: Focus on the Critical Chain
• Critical Chain Project Management advantages
  • CCPM increases performance
  • CCPM features some built-in risk management
• Critical Chain Project Management disadvantages
  • CCPM clashes with workplace cultures based on honesty and openness
  • CCPM does away with dates and milestones
  • CCPM favors the wrong project management skills
  • CCPM lacks in volume of case study statistics that support its promises
• Conclusion: CCPM builds upon CPM and requires commitment

The difference between the Critical Chain and the Critical Path

Before we can discuss Critical Chain Project Management in further detail, we must talk about the Critical Path Method as a point of reference.

This is because CCPM and CPM are very similar. You can think of CCPM as an extension of CPM.

If a project really did have infinite resources, its Critical Path and Critical Chain would be identical. But since this is rarely the case, CCPM seeks to paint a more realistic picture of the project schedule.

What is the Critical Path?

The Critical Path is the longest sequence of dependent tasks in a project. 

If we take task durations to be the only project constraint, we can use CPM to calculate the optimal Critical Path.

The duration of the Critical Path becomes the project’s deadline.

What is the Critical Chain?

The Critical Chain is the longest sequence of tasks in a project once the schedule has been leveled for resources. 

It’s also not necessarily a sequence of dependent tasks, as the Critical Chain also accounts for resource dependence.

Unlike with the Critical Path — where there is only one optimal and mathematically correct solution — the goal here is not to find the optimal Critical Chain. 

Due to the added variables, doing so would be impossible or difficult to the point of being counterproductive. 

Instead, the goal is to find a Critical Chain that’s good enough to see the project through.

How to manage projects with CCPM in 4 steps

To effectively manage projects using the CCPM methodology, you are required to follow these 4 steps:

1. Find the Critical Path
2. Level the resources
3. Implement buffers
4. Focus on the Critical Chain

Step 1: Find the Critical Path

As mentioned, Critical Chain Project Management can be thought of as an extension of the Critical Path Method.

Therefore, it should come as no surprise that calculating the Critical Path is the first step required for using CCPM.

The Critical Path shows us what the ideal task sequencing would look like if time were the only constraint and all other resources were unlimited.

While Critical Paths rarely coincide with Critical Chains in practice, we can still use them as a functional starting point for finding Critical Chains.

After all, it’s easier to take an existing framework and correct it for limited resource availability than it is to create a Critical Chain from scratch.

To calculate the Critical Path, you need to:

• Create a project Work Breakdown Structure,
• Perform the forward pass (used to calculate the early start and early finish values for each project task), and
• Perform the backward pass (used to calculate the late start, late finish, and total float for each project task).

💡 Plaky Pro Tip

Since Work Breakdown Structure, forward pass, backward pass, early start, early finish, and total float are complex steps that require guides of their own to properly explain, we suggest reading our guide on CPM, as well as this guide on Work Breakdown Structures before proceeding further:

• What is a Work Breakdown Structure (WBS) in project management?

Step 2: Level the resources

Use of resource profiles immensely helps find the Critical Chain.

These are bar charts that show us how project tasks are organized with regard to time (x-axis) and a specific resource (y-axis).

Leveling the resources entails putting a limit on the y-axis and rearranging the tasks so that they never go above it. In all likelihood, this will extend the project deadline calculated using the Critical Path.

Keep in mind that you’re not looking for the optimal rearrangement of tasks, as such an arrangement would be either impossible or prohibitively difficult to find. 

Your goal is to find a good enough arrangement of tasks.

How to level multiple resources at once?

Since resource profiles only have two axes, you’d think that they could only be used to level a single resource at a time.

However, a few simple tricks like using color and shading can effectively check for resource overuse without occupying the y-axis.

For example, you can assign a color to each member and use it to color the visual representation of resource profile tasks that they are assigned to. 

This way, you can easily spot if the Critical Path schedule needs the same person to work on multiple tasks concurrently and have that in mind as you rearrange tasks inside the resource profile. 

Ideally, no one person should be assigned to 2 or more tasks at the same time, as multitasking is shown to inhibit productivity.

Likewise, if you’re already using colors to mark task ownership but have to consider the use of a physical space — let’s say a conference room — as another limited resource, you can use shading to distinguish the tasks that depend upon the second resource. This way, you can easily make sure that no two tasks that require the use of the conference room are scheduled at the same time if you’ve only got one conference room.

The best way to prevent multitasking is by using a project management tool like Plaky to assign tasks to team members. With Plaky, you can set deadlines and monitor who’s doing what task, all while ensuring that no employee is assigned two tasks at the same time.

Once you’ve leveled the resources, you can see which tasks constitute the Critical Chain.

Step 3: Implement buffers

We know how to find the Critical Chain now, but there’s more to CCPM than just making the calculations.

Namely, this project management methodology also seeks to increase performance and measure progress.

Both of these goals are achieved simultaneously through the use of buffers.

Buffers are the extra resources you leave on the side in case something goes wrong and delays project tasks.

Traditional project management still allocates extra time to each activity to ensure any difficulties encountered along the way don’t affect the project timeline. 

For example, if a task is given an 8-day duration, the task can likely be completed within 4 or 5 days. The extra time is given to ensure unexpected wrinkles can still be ironed out without delaying subsequent tasks.

CCPM finds this approach suboptimal because of Parkinson’s Law, which states that “…work expands so as to fill the time available for its completion”. 

In other words, if a task was assigned an 8-day duration, then it will take 8 days to complete, even if it could have been completed faster on a shorter deadline, without sacrificing quality.

The use of buffers (especially project buffers) in CCPM serves the purpose of increasing performance by preventing Parkinson’s Law and student syndrome (the tendency to wait until the last minute to start working on a task) from festering.

There are 3 types of buffers in CCPM:

• Project buffers,
• Feeding buffers, and
• Resource buffers.

Project buffers

The project buffer is the most important buffer in CCPM, as it shows you how much extra time you have to complete the tasks inside the Critical Chain.

To find out what your project buffer is, take the project duration and split it in half.

If the project is calculated to take 50 days to complete, act as if you want to get everything done in 25 days. 

The remaining 25 days act as a buffer to help ensure you don’t cross the deadline. When a task inside the Critical Chain takes longer to complete, you detract the extension from the project buffer.

Keep in mind that the 50-day mark is still considered the deadline!

This is the number that is communicated to clients.

You shouldn’t even expect to finish the project within 25-days. This is not the goal.

The goal here is only to combat student syndrome and Parkinson’s Law, with the assumption that 50% of the task will take longer to complete but the other 50% won’t. This is where the extra productivity comes from.

The rate of project buffer expenditure is used to gauge how well the project is performing.

If a quarter way through the project, you’ve expended 25% of your project buffer, you are doing well and are on the path to meeting the 50-day deadline.

If a quarter way through the project, you’ve already expended 40% of your project buffer, you can take this as a sign that there is a problem and that you will not meet the 50-day deadline — unless you figure out what the problem is and address it.

Feeding buffers

Feeding buffers (also known as feeder buffers) are the equivalent of total float in CPM — they show you how much extra time you have for the completion of task sequences that aren’t on the Critical Chain.

The use of feeding buffers does not affect your total project buffer.

Last but not least, if adding a feeder buffer would result in creating a new Critical Chain, make the feeder buffer shorter. 

Feeder buffers cannot be part of the Critical Chain. They can only feed into it, hence the name.

Resource buffers

Resource buffers are placed within the Critical Chain to ensure critical activities have all the resources (time, equipment, etc.) they need.

Not every CCPM project will have resource buffers, since these are extra resources that the company or the client may not grant.

Step 4: Focus on the Critical Chain

By performing steps 1, 2, and 3, you’ll be able to identify the Critical Chain and monitor project progress.

Technically, the first three steps are enough to use CCPM.

However, none of this will function as intended unless you make sure the people performing critical tasks are free of all distractions.

The Critical Chain is often likened to a relay race — a team racing competition where multiple athletes stationed at different parts of the racecourse work in sequence to carry a baton across the finish line.

The comparison is apt, with team members acting as athletes and the baton acting as tasks within the Critical Chain.

In some CCPM teams, an actual baton — or some approximation — is passed off from person to person working on the Critical Chain. Seeing a team member with the baton should be taken as a sign not to disturb them with anything and to offer assistance if requested.

Virtual teams can still simulate this. 

For example, if the project team is using a team communication tool, they can update their status using an agreed-upon baton emoji ( 🏃). This emoji will be displayed next to their name and online status and act as the baton, similarly to how an icon of a hamburger shows when they’re on lunch break.

Critical Chain Project Management advantages

The main advantages of using CCPM are twofold.

Namely, this project management methodology:

• Increases performance, and
• Features some built-in risk management.

CCPM increases performance

In theory, the main advantage of Critical Chain Project Management is that it can increase performance by speeding up task completion.

In traditional project management, turning in tasks as soon as they are finished has no bearing on the project deadline.

If tasks A and B both take 10 days to complete and task C is dependent on both, then faster completion of task A won’t result in task C starting any sooner.

However, if tasks A and B are allocated 5 days to complete, with 5 days of buffer time on top of this, and they’re both completed without burning through any buffer time, then task C can start 5 days early.

CCPM features some built-in risk management

CCPM basically has some form of risk management baked into it, as all scheduling changes made by resource leveling are effectively risks you’ve avoided. 

Furthermore, due to the project buffer, CCPM allows project managers extra time to deal with unknown risks.

To clarify, CCPM is not a replacement for risk management and it doesn’t account for all potential risks.

You should still conduct proper risk management on any project. CCPM just aids these efforts a bit.

Critical Chain Project Management disadvantages

For all its advantages, though, CCPM is rife with disadvantages.
For example, CCPM:

• Clashes with workplace cultures based on honesty and openness,
• Does away with dates and milestones,
• Favors the wrong PM skills, and
• Lacks in volume of case study statistics that support its promises.

CCPM clashes with workplace cultures based on honesty and openness

CCPM works under the assumption that employees either lie about how long it takes them to complete tasks or are inept to make realistic predictions.

If an employee estimates a task will take 10 days to complete, the project manager will only put 5 days on the project schedule. They’re ready to give back the extra 5 days that went into the buffer, but you can see how this whole exchange can breed hostility and bitterness within the team.

And, the more honest and accurate employees are in their task duration predictions, the worse CCPM gets.

CCPM does away with dates and milestones

It’s not just the team members that need to get on board with radical changes required for CCPM project management. Executives also have to get comfortable with the idea of not using dates and milestones in favor of buffer-based progress tracking.

Buffer expenditure causes CCPM schedules to constantly change. This means milestones and dates would constantly shift, causing the project to appear worse for wear even if the project buffer shows everything is fine.

The project manager knows this, but clients and executives aren’t necessarily people with intimate knowledge of CCPM. They prefer the simple-to-understand and no-nonsense nature of dates and milestones over the amorphous nature of project buffer progress signaling.

CCPM favors the wrong project management skills

In their paper titled “A Critical Look at Critical Chain Project Management”, the authors concluded that project performance depends less on the PM’s skill for managing the schedule constraints and more on their interpersonal and leadership skills. 

CCPM, by its very nature, sabotages the good relations between PMs and team members required for interpersonal and leadership skills to shine.

This isn’t to say that scheduling skills aren’t important — just that they shouldn’t come at the expense of soft skills that also contribute to project performance.

💡 Plaky Pro Tip

To do their job properly, PMs are required to excel at many soft and hard skills. You can find the complete list of PM skills here:

• What are project management skills?

CCPM lacks in volume of case study statistics that support its promises

Last but not least, there is a striking lack of case study data confirming the effectiveness of Critical Chain Project Management. 

Of course, there are some positive case studies. Japanese construction companies have used CCPM to great effect, cutting costs and completing work faster.

However, such case studies are few and far between, especially if we narrow them down by industry.

All of this is to say that, while the advantages of CCPM check out in theory, we lack substantial data that details the effects it has in practice. The same cannot be said about other project management methodologies. 

Conclusion: CCPM builds upon CPM and requires commitment

Critical Chain Project Management helps to create a resource-oriented project plan that accounts for many of the things that CPM simply doesn’t take into consideration.

If you stop at step 2 of our guide to CCPM — leveling the resources — you can use it simply as a scheduling algorithm and still overcome some of the limitations of CPM.

However, unlike CPM and PERT, CCPM is not merely a scheduling algorithm. 

The moment you implement buffers, it becomes a fully-fledged project management methodology that asks you to abandon milestones and reduce team members’ task duration estimates for the chance to increase productivity. 

All this is to say that CCPM is a methodology that can work, but that requires complete corporate and employee buy-in to function properly.

References

• Critical Chain Concepts. (n.d.). Scitor Corporation. Retrieved June 6, 2022, from http://www.zeusconsult.com.mx/critical_chain_concepts.pdf 
• Heptinstall, I. (2012). Construction Procurement and Project Management in Japan’s Public Sector. “Win-Win-Win”, A case study in collaboration and change. PM World Journal, 1(1). https://pmworldlibrary.net/wp-content/uploads/2013/02/PMWJ1-Aug2012-CaseStudy-HEPTINSTALL-ProcurementiInJapansPublicSector.pdf
• Parkinson, C. N. (2020, July 10). Parkinson’s Law. The Economist. https://www.economist.com/news/1955/11/19/parkinsons-law
• Raz, T., Barnes, R., & Dvir, D. (2004). A Critical Look at Critical Chain Project Management. IEEE Engineering Management Review, 32(2), 35. https://ieeexplore.ieee.org/document/1302743
• The critical path or the critical chain? The difference caused by resources. (n.d.). PM Knowledge Center. Retrieved June 8, 2022, from http://www.pmknowledgecenter.com/dynamic_scheduling/baseline/critical-path-or-critical-chain-difference-caused-resources
• Verma, E. (2022, March 14). What is Critical Chain Project Management. SimpliLearn. https://www.simplilearn.com/what-is-critical-chain-project-management-rar68-article