What Is Critical Path in Project Management?

Prioritizing tasks can be tricky. While some activities may look heavier than others, it doesn’t always mean those tasks require the most attention. An important thing to consider is dependencies, or tasks with outputs that are required to start other tasks. Taking dependencies into consideration can make estimating a project’s duration and prioritizing tasks more complex. One useful technique to manage this is the critical path method.

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What Is the Critical Path Method?

The critical path method is the process of identifying the string of tasks and dependencies that take the longest time to complete in a project. This group of to-dos is called the critical path, while the tasks inside it are called critical activities.

The total duration of the critical path is the minimum time you’ll need to complete a whole project. Any delay for critical activities will result in extending the total project duration.

How to Identify a Project’s Critical Path

You can find your project’s critical path by using project management tools that use algorithms to find it for you. However, you can also calculate critical path by doing a forward and backward pass.

Step 1: List All Project Tasks

Start by breaking your project down into milestones, deliverables, and actionable tasks. This helps you visualize the day-to-day activities you and your team have to accomplish to progress.

Here’s an example of all the tasks associated with planning an online press conference:

Step 2: Identify Dependencies and Estimates

Once you have all project tasks laid out, identify dependencies, or the tasks that can’t proceed without another’s output. List them out in a table, along with an estimate of how long each task would take.

Returning to the example above:

Step 3: Use a Network Diagram That Traces Dependencies

A network diagram is a series of boxes and arrows that help visualize the connections of specific variables. In this case, it’s used to represent tasks and their relationships.

Dependencies point to the tasks that can proceed once they’re finished. For example, “Collect contacts to publications” (Task 1) points to “Send out invites” (Task 3) because Task 3 can only proceed once Task 1 is finished.

Step 4: Do a Forward Pass

There are two variables to consider when doing a forward pass:

• Early Start Time (ES): The earliest time a task can start
• Early Finish Time (EF): The earliest time a task can finish

In the diagram, put each task’s ES at the upper-left corner and its EF at the upper-right.

To get the EF, simply add the duration of the time to the ES. So, if Task 1 can start at day 0 and take 0.5 days to finish, then ES = 0 and EF is 0.5.

As for Task 3, the earliest time it can start is when Task 1 is completed. So, Task 3’s ES is 0.5. With a 0.5 day duration, its EF is 1.

If there are conflicts where three tasks are pointing to it, as is the case with Task 11, pick the highest EF as its ES.

In the above example, Task 3’s EF is 1, Task 5’s is 1.5, and Task 10’s is 6. Because 6 is the highest EF, this will be Task 11’s ES.

Step 5: Do a Backward Pass

Once you’re done with the forward pass, you may now do the backward pass; however, there are two new variables to consider:

• Latest start time (LS): The latest time that a task can be started without delaying the whole project
• Latest finish time (LF): The latest time a task can be finished without delaying the project

In the network diagram, the LS is at the lower-left side of the task, while the LF is at the lower-right side of the task.

To start computing for each task’s LS and LF, begin by copying the last task’s EF as its LF. In our case, copy Task 11’s EF (6.5) at its upper-right side, and write it on the lower-right side as well.

Find the LS by subtracting the duration from the LF. In Task 11’s case, LS is 6.

Use task 11’s LS as the LF of all the tasks pointing to it: Task 3, Task 5, and Task 10. Subtract their durations to find their LS, respectively.

For tasks that point to more than one task, use the lower LS as its LF.

An example of this is Task 1. It points to both Task 3 and Task 10. When doing the backward pass, you’ll see that Task 3’s LS is 5.5 and Task 10’s LS is 5. Because of this, Task 1’s LF is 5.

Step 6: Find the Critical Path

To know your project’s critical path, look for the tasks with the same EF and LF. This means that the earliest time it can finish is also the latest time it can finish; therefore, it can’t be delayed.

In this case, the critical path is the creation of the press release:

• Press release outline (Task 6)
• Draft press release (Task 8)
• Finalize press release (Task 9)
• Send out press kit (Task 10)
• Implement press conference (Task 11)

For non-critical activities such as Task 4 (confirming speakers and panelists), failing to finish on day 1 (EF) wouldn’t extend the duration of the project as a whole — as long as it’s finished on or before day 5.5 (LF). But for a critical activity such as Task 9, failing to finish on time will result in the press conference as a whole being delayed.

Read more: Top 5 Steps for Creating a Successful Project Schedule

Benefits of the Critical Path Method

• Prioritizing tasks: Knowing your critical activities will help you identify those tasks you’ll need to pay close attention to and avoid delaying.

• Anticipate and avoid bottlenecks: Laying out tasks and their dependencies can help you anticipate possible bottlenecks you can avoid when you’re scheduling or resource planning.

• Identify slack: Slack, also known as float, is the number of days a task can be delayed before it affects the project’s entire timeline, which can be found by subtracting the EF from the LF.

Limitations of the Critical Path Method

Resource Dependencies

The network diagram used to identify the critical path visualizes process dependencies. What it doesn’t illustrate, however, is resource dependencies.

An example of resource dependency is if there’s only one person assigned to do two tasks. Because of this, one task can’t be started until the person finishes the other. These types of dependencies need to be considered when estimating a project’s duration, as well.

Schedule Interruptions

Another dependency the network diagram doesn’t illustrate is time dependencies, such as seasonal interruptions like software maintenance, office closure, holidays, and others. In short, work can’t resume until they’re finished, so these should also be considered when estimating a project’s duration.

Read more: Significance of Keeping Documentation in Project Management

A Great Method for Planning a Project Timeline

The critical path method is a good way to identify the minimum time you need to finish a project. It also points out your critical activities, or tasks that can’t be delayed without compromising your project’s deadline.

Find your project’s critical path automatically through project management software, like the tools listed below, or manually through a forward and backward pass.