Understanding Critical Path Method in Simple Words

When we work on project, there are many tasks to do. Some tasks take long, some take short time. Some can be done together, some must wait for others to finish. In this situation, how we know which tasks are most important? Which tasks cannot be delayed at all?

The answer is: critical path method.

This method helps project managers plan and control the schedule. In this article, we explain critical path method, why it is useful, and what are the two types of it – one based on longest path, and one based on total float = 0.

What Is Critical Path Method?

Critical path method, also called CPM, is a way to find the most important tasks in a project. These tasks must be done on time, otherwise the whole project gets delayed.

In simple words, critical path is the longest path in the project schedule. It shows which activities decide the total duration of project. If one of these tasks is late, the project is also late.

Each task in project has early start, late start, early finish, late finish, and float (also called slack). Float means how much delay is okay without affecting project.

Tasks on the critical path have zero float – they cannot be late at all.

Why Critical Path Method Is Important

Using critical path method helps in many ways:

• You know which tasks need full focus

• You avoid project delay by watching the right tasks

• You can plan resources better

• You can manage risks earlier

• You can explain timeline clearly to client or team

So CPM is not just a theory. It is very practical and useful in every kind of project – construction, software, events, product launch, and more.

Two Types of Critical Path Method

In project management, there are actually two ways to define the critical path. Many people don’t know this, but both ways are used in real projects.

Let’s understand them one by one.

1. Critical Path Based on Longest Path

This is the most common method. In this, critical path is the longest path from start to end in the project schedule.

Here, “longest” means total duration in days, weeks, or hours – not number of tasks.

You find all possible paths from project start to finish. Then check which one takes most time. That path is your critical path. Any delay in it will delay the full project.

Purpose: This method is useful to see overall schedule length and where the time is tightest.

Example:

• Path A-B-C takes 15 days

• Path D-E-F-G takes 18 days

• Path H-I-J takes 12 days

So critical path is D-E-F-G because it is longest (18 days).

Good for: Large projects with many paths where time is more important than float.

2. Critical Path Based on Total Float = 0

In this method, you find all tasks that have zero total float. Total float means the time a task can be delayed without delaying the project.

If total float is zero, it means task is critical. Even 1-day delay will delay project.

Here, you don’t only look at path length, but check float of each activity. If float is zero, task is part of critical path.

Purpose: This method is useful when you want to see task-level risk, not just path.

Example:
Let’s say Task X has float 0 → It is critical
Task Y has float 2 → It is not critical
Task Z has float 0 → It is critical

Good for: Projects with more detailed planning where float matters more than duration.

Key Difference Between Two Methods

Sometimes both methods give same result, sometimes not. In complex projects, float-based method gives more clear picture.

How to Find Critical Path in Real Life

Many tools like MS Project, Primavera, and even some Excel templates can calculate critical path method for you. But still, it is good to understand the logic behind:

1. List all activities with durations

2. Show dependencies (which task depends on which)

3. Create a network diagram

4. Do forward pass (to find early start and finish)

5. Do backward pass (to find late start and finish)

6. Calculate float for each task

7. Find longest path or tasks with float = 0

Once you know the critical path, update it regularly. If project changes, critical path also changes.

Tips for Using Critical Path Method

• Keep schedule realistic – don’t make all tasks critical

• Add buffer (contingency) outside critical path

• Watch the critical path regularly, not just one time

• Communicate with team which tasks are critical

• If possible, reduce critical path to save time

In simple words, critical path method is like project heart. If it is healthy, project runs smooth.

Final Words

Critical path method is one of the most useful tools in project management. It helps to find which tasks must be done on time. There are two ways to define it – by longest path and by total float = 0.

Both methods are good, and which one to use depends on your project type. Some projects need focus on timeline, some need focus on flexibility.

Knowing the critical path method gives you more control, more confidence, and better chance of finishing project successfully. It is a must-know for every project manager.