Hi,

today I will show you relation between Slack and Costs using MS PROJECT 2019 / Online.

First I will create new Project

and some Resources:

Finally, I will assign Resources to Tasks:

Using Format Tab, I will show Critical Tasks, and Slack:

OK. What is Critical Path (Task are marked red!)? It is path in which, if any activity will be late, the whole Project will be late, e.g. Project finish date will be “damaged”!

On the other hand, slack is amount of time which I have in some path, when Tasks can be delayed without jeopardizing Project finish date!

So, as you can see, all Tasks on Phase 1 are on critical path, and this path determines the duration of the Project, and Finish date (9 days Duration, and Finish date is 26.03.2020)

On the other hand Phase 2 has slack 3 days (6 days Duration, and Finish date is 23.03.2020).

Let me show you Costs. To do that, I will apply Cost Table:

As you can seem Total Cost of Task 6 is $14.400. This is because, Task 6 has Duration = 3 days, and Jim is going to work 8 hours per day, e.g. 3 Days * 8 hours / Day = 24 hours! Since cost per hour for Jim is $600, Total Cost for Task 6 is 24 hours * $ 600 = $ 14.400

Now, let’s say that Task 6 will last 5 Days instead of 3 Days:

As you can see, Project Finish date remains the same (e.g. 26.03.2020), Phase 1 will finish 2 days later (e.g. 25.03.2020), and Finish date is not jeopardized .

BU! Let’s say Cost Table again:

As you can seem Total Cost of Task 6 is now $24.000. This is because, Task 6 has Duration = 5 days, and Jim is going to work 8 hours per day, e.g. 5 Days * 8 hours / Day = 40 hours! Since cost per hour for Jim is $600, Total Cost for Task 6 is 40 hours * $ 600 = $ 24.000.

So, when you have a Slack, it means that some Task can last longer without “moving” Project Finish date, but it doesn’t mean that Cost are going to remain the same.

And, for the end of this post, lets, say that Task 6 will have 9 days Duration:

Now, Critical path is changed, so all Tasks at Phase 2 are on it. Project Duration is 12 days, and Finish Date is determined by Phase 2 (e.g. 31.03.2020). And Phase 1 has Slack 3 days!

To conclude, lot of people think that if you have a Slack than you are in a “comfort zone”. It is not a case!

Regards!