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