This post was originally published on January 22, 2019, and updated most recently on March 20, 2021.
Every project is made up of different tasks, some of which are dependent on each other (i.e., tasks you can’t start until the previous task has been completed). While the execution of certain tasks can greatly impact a project’s completion date, others have more flexible timelines.
With so many jobs flying around, it’s perilously easy to become distracted and overlook crucial project-dependent tasks. This is where the critical path method (CPM) comes in.
What is a critical path?
In a nutshell, the critical path method, or CPM, helps you identify the most important tasks and then work out the quickest way to complete a project. It’s commonly paired with the Process Evaluation Review Technique (aka the PERT chart).
To work out your critical path, you simply identify the longest stretch of dependent tasks. This gives you a kind of ‘bare minimum’ timeframe, which you can then use to schedule your project.
Adopting the CPM has three overarching benefits:
- It cuts out distracting noise and identifies the most important tasks.
- It’ll uncover your tasks’ interdependencies.
- It identifies which tasks will benefit from duration reduction, which helps you reduce your overall timeline.
A real-life example
To use a simple dessert-based analogy: In order to make a cake, you need to break some eggs, whisk, mix with flour and butter, then bake. You can’t cover it in frosting until you’ve done these other steps. These are all dependent tasks. Meanwhile, you need to wash the dishes and find a cake tin. The cake will take the longest, and the tasks that go into making it are the most important, so work out the time it’ll take to complete from start to delicious finish, and you’ll have your critical path. This is the least amount of time your project will take. Phew!
Who can benefit from the critical path method?
Anyone working on a project — whether that’s an hour-long cake baking session, a month-long construction job, or a year-long app development project — can benefit from prioritizing the right tasks in the right order.
Okay, maybe an hour-long cooking session isn’t worth the time it takes to work out the critical path, but it’s definitely worth the effort for bigger projects with several streams of dependent tasks.
Critical path glossary
Before we get into the ‘how,’ let’s quickly run through the terms you need to know.
- Earliest start date: The earliest date or time a task can begin. The first one in the project is easy enough to work out, but to calculate the earliest start dates for the other tasks, you’ll need to figure out how long it’ll take to complete each preceding one.
- Earliest finish date: Work out how long it’ll take to complete each task, and you’ll have your earliest finish date(s).
- Latest start date / latest finish date: This is the latest possible time you can start a task before it threatens to derail the overall project. Similarly, latest finish date is the longest time you can take to complete a task before it starts impacting the other tasks in the project.
- Float or Slack: This refers to the amount of time a task can be delayed before it causes an overall delay or impacts the other tasks. When you’re analyzing tasks to work out your critical path, they should have zero float. If they do, then take them out of your critical path. This means that if your project experiences a delay, everything can still finish on time.
- Crash duration: This describes the shortest amount of time in which you can complete a task. You achieve this by directing more resources toward the completion of the project or place an emphasis on speed over quality.
- Critical path drag: This has a dual meaning. It refers to both the amount of time a task constraint will add to the project duration and to how much longer a project will take because of the task and constraint.
How to calculate critical path
Now that you know the ‘whats’ and ‘whys,’ it’s time to take a deep dive into that ‘how.’ First thing’s first: Your critical path model will include the following four steps:
- Create a list of each and every activity that goes into completing the finished project. These are usually categorized within a work breakdown structure.
- Record the amount of time it’ll take to complete each task.
- Determine all task dependencies.
- Take note of all the milestones and deliverable times.
- Update your critical path diagram as your project progresses.
Once you have all this info, you’re ready to calculate your critical path. You can also work out which tasks are critical and which can feasibly be delayed without impacting the overall project (float). Once you have your critical path up and running, you can then:
- plan your schedule,
- allocate resources and budget,
- create a project proposal,
- conduct the project’s risk assessment and accurately predict task-dependent delays,
- identify resource conflicts and hidden dependencies,
- accurately predict your project’s completion date, and
- compare your planned schedule with your actual schedule.
Changes to your critical path
As with anything in life, projects are often unpredictable. Even a perfectly laid out critical path can be subject to change with the unforeseeable pops up. Maybe you ran out of resources for one step or one team member was unable to deliver a task on time. It’s important to remain as flexible as possible when this happens.
Any of these scenarios will obviously change some of the aspects of your plan, a due date here, a completion there. But it’s also possible that it will change your overall critical path. If you have to bypass a step or rearrange some of your steps, it’s possible that your critical path itself will change. It might involve different steps or splinter off in a different direction than you had originally calculated. It’s important to stay mindful of this and be ready to change if the need arises.
Keeping your critical path on track
Your critical path isn’t set in stone. As you’ve probably come to learn, tasks change, schedules change — you can’t predict everything. This is why you must monitor your critical path as you go.
There are two ways you can go about this.
- Create a network diagram, which shows you all the tasks that make up your project, along with their dependencies, start dates, and end dates. While network diagrams are extremely useful tools, when it comes to the critical path method, they can be a little cumbersome. That’s because you’ll need to dedicate a significant chunk of time to calculate all the different variables. Which brings us to your second option…
- Let your project management software do the heavy lifting! Okay, we realize not everyone has project management software, in which case, option one is your only choice. But if you do, then you’re in for a treat. Simply open up your advanced Gantt chart settings, automate your critical path calculations, then filter your chart so it shows only the relevant tasks. And voilà, it’s that easy!
Looking to invest in some project management software? Backlog has cloud-based sharing options and plenty of automation tools that help you crunch data and track your projects in real-time. Not only will this help you save time, but you’ll be able to share your plans and adjustments with the wider team, so everyone’s on the same page every step of the way.