How to Find the Critical Path

The critical path method (CPM) is a way for project managers to make a schedule and estimate how long a project will take as a whole.

The CPM method, also called critical path analysis (CPA), uses a network diagram to show how the tasks needed to finish a project need to be done in order. Once these task orders or paths are set, their lengths are calculated to find the critical path, which tells how long the whole project will take.

CPM Key Elements

Before we can learn how to figure out the critical path, we need to know a few important CPM concepts.

Earliest start time: This is the earliest time that a task in your project can be started. You can’t figure this out until you know if any tasks depend on each other.

Latest start time (LS): This is the very last minute you can start a task before it threatens to push back the schedule for your project.

Earliest finish time (EF): The earliest a task can be finished, based on how long it takes and when it begins.

The latest time an activity can be finished, is based on how long it takes and when it started.

Float, also called “slack,” is a term for how long you can put off a task before it affects the order of other tasks and the project schedule. Tasks on the critical path have no wiggle room because they can’t be put off.

How to Find a Project’s Critical Path in 8 Steps

1. Collect Project Activities

Use a work breakdown structure to keep track of all the project tasks that lead up to the final product.

2. Identify Task Dependencies

Find out which tasks can’t start until you’ve done something else. Use your own judgement and what your team says. If you don’t correctly define how tasks depend on each other, the critical path method is useless.

3. Make a Critical Path Diagram

A network diagram or critical path analysis chart shows the order of events.

4. Estimate Timeline

To use the critical path method, you have to guess how long each task will take. Use information from past projects and other sources, like experts in the field, to help you figure out what to do.

5. Use the Critical Path Algorithm

There are two parts to the critical path algorithm: a forward pass and a backwards pass.

Forward Pass

Use the network diagram and an estimate of how long each activity will take to figure out when it will start and when it will end (EF). The ES of an activity is the same as the EF of the activity that came before it. The EF of an activity is found by the formula EF = ES + t. (t is the activity duration). The EF of the last activity shows how long it is expected to take to finish the whole project.

Backward Pass

Starts by making the earliest finish time of the last activity its latest finish time. The formula for finding the LS is then LS = LF – t. (t is the activity duration). For the activities that came before, the LF is the earliest start time for the activity that comes right after it.

6. Identify the Float or Slack of Each Activity

Use this formula to figure out how much time each task gives you. Float = LS – ES

7. Identify the Critical Path

The critical path is made up of tasks that can’t be moved around. Except for the first task on your CPM schedule, all of these tasks on the critical path depend on each other. All project tasks that have more time than they need are not on the critical path.

8. Revise During Execution

As you move through the execution phase, keep making changes to the critical path network diagram.

These steps of the critical path analysis help figure out which tasks need to be done right away and which ones can be delayed without hurting the project schedule. Now that you know what you need to know, you can plan the critical path schedule better and have a better chance of finishing your project on time.

You should also think about any other changes or restrictions that could affect the project schedule.

The better your critical path schedule will be, the more you can plan for these unexpected events or risks. When these constraints add time to a project, it is called a “critical path drag,” which is how much longer the project will take because of the task and the constraint.

Critical path analysis has these pros

• Find out what tasks depend on each other, what resources can’t be used, and what risks the project has.

• Figure out how long each task will take.

• Set the order of tasks based on how much free time they have. This helps with project planning and allocating resources.

• Find the most important tasks that can’t be put off and make sure they are done on time.

• Watch how your project is going and see how the schedule is changing.

• Use techniques like crash duration or fast-tracking to squeeze more into your schedule.

Conclusion

Projects are made up of tasks that need to be done on time and according to a plan. It sounds easy, but if you don’t map out the work, the scope of your project can quickly get out of hand, and your project will get off track.

When managing a project, it’s important to use the critical path method because it helps you figure out all the tasks that need to be done to finish the project, which ones must be done on time, which ones can be put off if necessary, and how much float or slack you have.