How to Calculate Slack Time in Excel (2 Ideal Examples)

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Slack time is a significant factor in project management. To finish a project on time, finding slack time is reasonably necessary. If you don’t know what slack time is and how to calculate it then you have visited the right place. In this tutorial, we’ll demonstrate the easiest way to calculate slack time in Excel with a proper example.


Introduction to Slack Time: Definition and Formula

Definition:

Slack time is the time difference between the necessary date to accomplish the critical path and the fixed completion date. Simply we can say that slack time in PERT analysis is the amount of time that can delay the finishing of a task without delaying the other tasks or without affecting the fixed deadline of a project.

Float is also called Slack, both are the same in project management.

Slack Time Formula:

Simply, the slack time formula is equal to the difference between the latest start date and the earliest start date. So, the formula is:

  • Slack Time = LST – EST

Where,

  • LST is “Latest Start Time”.

The time when an activity can be started as late as possible except affecting the deadline of the project.

  • EST is “Earliest Start Time”.

The time or date when an activity can be started as early as possible if the predecessors can complete before their set finish time.

There is another way to find the slack time, that will result in the same:

  • Slack Time = LFT – EFT

Where,

  • LFT is “Latest Finish Time”.

The time or date when an activity can be completed as late as possible except affecting the total project deadline.

  • EFT is “Earliest Finish Time”.

The time when an activity can be finished as early as possible.

Also, we can say it is the Activity Slack Formula. “Activity Slack” and “Slack Time” mean the same thing.


How to Calculate Slack Time in Excel: 2 Suitable Examples

Now we’ll demonstrate a practical example to learn how to calculate the slack time for each activity of a project. The dataset contains the EST, EFT, LST, and LFT of 11 activities of a project.

How to Calculate Slack Time in Excel

Read More: How to Calculate Elapsed Time in Excel


1. Calculating Slack Time Using the Start Time in Excel

Firstly, we’ll calculate the slack time using the start time of the activities. We already know that the slack time is equal to the difference between the latest start date or time and the earliest start date or time, so we’ll apply this formula in Excel.

Steps:

  • Insert the following formula in Cell G5
=E5-C5
  • Next, just hit the Enter button to get the slack time for the first activity.

Calculating Slack Time Using the Start Time

  • Then to calculate the slack time of the other each activity, just drag down the Fill Handle icon to copy the formula.

Use Fill Handle Tool for Calculating Slack Time Using the Start Time

Here’s all the slack time for each activity.


2. Calculating Slack Time Using the Finish Time in Excel

We can calculate the slack time using the finish time too. So here, we’ll find the difference between the latest finish date or time and the earliest finish date or time.

Steps:

  • In Cell G5, type the following formula-
=F5-D5
  • Later, press the Enter button for the output.

Calculating Slack Time Using the Finish Time

  • Finally, use the Fill Handle tool to copy the formula to calculate the slack time of the other each activity.

Use Fill Handle Tool for Calculating Slack Time Using the Finish Time

Have a look, we got the same output.


Importance of Calculating Slack Time

  • Calculating slack time in project management helps to finish a project on time.
  • It helps to determine the available time within the activities.
  • It can shorten the PERT chart to improve productivity.
  • Slack time can increase productivity and efficiency in project management.

What Is Slack Time in Critical Path?

After evaluating the slack time for all the activities in project management, we choose a path that has zero slack time for each activity, that path is the critical path.


Difference Between Free Slack and Total Slack

Free Slack: It is the amount of time an activity can be delayed except by delaying the deadline of succeeding tasks.

Total Slack: It is the amount of time an activity can delay except delaying the deadline of the project. “Slack” or “Float” also means total slack.


Download Practice Workbook

You can download the free Excel workbook from here and practice independently.


Conclusion

That’s all for the article. I hope the procedures described above will be good enough to calculate slack time in Excel. Feel free to ask any question in the comment section and please give me feedback.


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Md. Sourov Hossain Mithun
Md. Sourov Hossain Mithun

Hello! I am Md. Sourov Hossain Mithun. Currently, I am working at Exceldemy as an Excel and VBA Content Developer. Excel is an amazing software to learn or work. Here, I will post Excel related useful articles. I am a graduate of Bangladesh University of Engineering and Technology. I love to learn new things and work with them. Thank you.

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