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Slack in Microsoft Project 2013

You may be wondering why you can have individual items with slack in your schedule but then have total slack for the whole project show zero. Is there a way to show on your schedule how many days of slack you have for the entire project? The answer is complicated.

First, some basics. Slack is the available time that a task can be delayed (or extended in Duration) without changing the project Finish date.

Now, here’s how to work with slack in Project 2013. First, we’ll create a brand new Project and look at it in the Detailed Gantt View:

Nenad Trajkovski Slack figure 1

As you can see, the project Start date is Tuesday, November 25, 2014 and the project Finish date is Wednesday, December 10, 2014. The total duration is 12 days. Why? Because Tasks 1, 2 and 3 are on the critical path! Critical path is the path on which if any task is delayed, the whole project will be delayed.

Now let’s extend Duration for Task 3 from three days to eight days:

Nenad Trajkovski Slack figure 2

That changes the Finish date to Wednesday, December 17, 2014. The total duration is 17 days.

Notice that Tasks 4, 5 and 6 have 11 days of Total Slack! So if we extend, for example, duration for Task 4 from one day to seven days, we’ll get:

Nenad Trajkovski Slack figure 3

You can see that Finish date is the same, but Total Slack time for tasks 4 through 6 is now five days.

Task 7 still has 16 days of Total Slack.

So why does the Project Summary Task (Task #0) show Total Slack as zero? Because Total Slack is not the sum of all slacks; it must be zero because on every project there is a critical path, and on the critical path, there is no slack! Because there is no slack, the Total Slack is zero.

Now for the complication. In this example, what is Total Slack? Is it 16 days (because that’s the longest slack on Task 7)? Is it five days (because that’s what it is for Tasks 4 through 6?? Or is it 21 (the sum of those two slacks)? Or is it 31 (the sum of all slacks)? It doesn’t make sense at all to have Total Slack for the entire project to be different than zero.

Written by Nenad Trajkovski

MVP – Project

Nenad Trajkovski was born in Zagreb in 1963. year. After completion of Faculty of Electrical Engineering, Nenad has started on the development and implementation of enterprise systems (ERP) in companies of various areas (banks, card houses, production companies, auto industry, wholesale businesses, oil companies, and others). He has extensive experience in working with business processes, people and knowledge in information technology and financial accounting activities.

Currently, Nenad works as a consultant for the implementation of business systems, and as Project Manager. He is trainer for Project Management and Risk Management in Microsoft Innovation Center in Varaždin. At WinDays08 conference he has been declared as the best speaker, and his session as the best one. He was among TOP 10 speakers in the Microsoft Sinergija 2009 and at the Microsoft Vzija 2009. Shared first place as the best lecturer at KulenDays 2009 and the PMI Forum 2009 in Zagreb. Regular speaker at the Microsoft Community. On WinDays10 conference Nenad was among the top three speakers; at the conference Microsoft Vision 9 in Skopje between the top 5 speakers as well as on Microsoft Synergy 11 which was held in Belgrade. Certified Accountant, PMP (Project Manager Professional), PMI – RMP (Risk Manager Professional), MCP (Microsoft Certified Professional), MCTS – Microsoft Project 2010 (Microsoft Certified Technical Professional).  and MCT (Microsoft Certified Trainer).

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1 Comment
  1. So I understand that MS Project is showing sack at the task level throughout the project, is there a way to remove the slack throughout the project and apply it at the end of the project as a project buffer?

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