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# calculate Sum of all slack in ms project

## Microsoft Project

#1
05-09-2011
 Member Join Date: Nov 2008 Posts: 2
calculate Sum of all slack in ms project

Hi all,

I'm trying to calculate the sum of all the slack between two milestones (i.e. how many days milestone 1 can be delayed before it effects milestone 2). They are linked together by a number of activitivies of varying durations, with 'gaps' between end dates and start dates due to other constraints. The two milestones are not on the critical path so total slack does not give me the answer, neither does free slack, because the tasks are also linked to other activities outside of this strand.

I'll try and give a simple example, all items are linked together sequentially, and i have included weekends as working days just to keep the maths simple.

Milestone 1 - 1/05/11 - no days slack
task a - 01/05/11-31/05/11 - 10 days slack (only showing 2 days slack because it's linked to another task starting on 02/06, which is part of another strand linking to a completely different milestone)
task b - 10/06/11-15/06/11 - 5 days slack
task c - 20/06/11-30/06/11 - 5 days slack
Milestone 2 - 15/07/11 - 15 days slack

There is the method of just increasing the start date of milestone 1 until milestone 2 changes, but it's not exactly scientific...any suggestions would be most welcome!

thanks...Luni.

#2
05-09-2011
 Member Join Date: Dec 2007 Posts: 1,728
Re: calculate Sum of all slack in ms project

Add the Start Slack and Finish Slack fields to any task view when you want to review how free slack was calculated. The Start Slack field contains the duration representing the difference between the early start and late start dates. The Finish Slack field contains the duration representing the difference between the early finish and late finish dates. More information can be found here.
#3
05-09-2011
 Member Join Date: Nov 2008 Posts: 2
Re: calculate Sum of all slack in ms project

Hi James,

Thanks for the response, unfortunately, I can't use the Finish slack figures. See my example...
the sum off all the slack between the two milestones is 35 days, however, because 'task a' has two successors (one of which is not in the strand of the two milestones), it is showing only 2 days slack, not 10. Thus giving me 27 days slack overall, this is not correct.

I've attached an example gantt to demonstrate what I mean.
Attached Thumbnails

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