In this lesson, we will discuss working with Date Constraints and Deadlines. Both may be useful when building a dynamic schedule.
As mentioned in the section on Backward Pass Calculations and Finish Date Constraints, a Must Finish On Constraint Type with the Constraint Date set to the project due date, is the preferred method to assign the project due date. Below we will demonstrate the reason.
Following this, we will show how Deadlines can be used for assigning interim due dates. Interim due dates are key task and milestone dates within the schedule that we are trying to meet. For example, our sponsor has requested that we deliver the Project Management Plan by a specific date.
A Deadline will show a green arrow in the Gantt Chart area on the Deadline date, and if the Finish date is later than the Deadline, will show a warning icon in the Indicators column.
Deadlines are set in the Task Information dialog under the Advanced tab, just above where the Must Finish On constraint is set.
Using a Must Finish On, versus a Deadline, versus no finish date constraint for our project due date:
The example below illustrates the reason we recommend assigning your project due date with a Must Finish On constraint.
We have a project that our Sponsor has indicated must be complete by February 3, 2023. Our current forecast Finish (Early Finish) for our project is 1/27/23.
We show three scenarios:
- No finish date constraint.
- Deadline date.
- Must Finish On constraint.
These three methods provide varying results:
- Using no finish date constraint provides NO visibility to our due date of 2/3/2023. The Total Slack is 0 for the entire path.
- Using a Deadline date of 2/3/23 displays a green arrow at the due date but provides NO information about the number of days between when we are currently scheduled to finish (1/27/23) and our due date (2/3/23). The Total Slack is 0 days for the entire path.
- Only by using the Must Finish On constraint do we have visibility to our due date with milestone E (our Target Complete milestone), our current finish date (1/27/23 on our Project Complete milestone) AND a quantified value (Total Slack = 5 days) that represents the difference between when we CAN finish (1/27/23) and when we MUST finish (2/3/23).
The scenario using no finish date constraint, and the scenario using the Deadline, show no changes to reflect the fact that we now have 3 additional days to complete our project.
In both cases, we see the impact to the Total Slack and are able to understand, and quantify, that based on our current plan, we will finish 3 days late.
With the Deadline, there is also a warning indicator displayed.
What this indicates is that your Total Slack is going negative. The default choice highlighted is Cancel. NEVER select the default! Always change it to Continue, so that you can see the resulting impact to the project.
Total Slack will always be 0 or negative if a Deadline is assigned for the project due date.
** Best practices:
- Always assign the due date of your project with a Must Finish On Constraint Type with a Constraint Date set to the project due date to enable the Total Slack on your critical path to be correct, whether it is positive, negative, or zero.
Interim Project Due Dates
Your project may have additional key dates that need to be represented in your schedule. These may include contract dates, gate dates, and other dates that you have committed to your customer or sponsor.
Deadlines may be used to specify these dates in your schedule. We will demonstrate how this works with a simple schedule model.
This schedule has 2 paths, and a Must Finish On (MFO) Constraint Type assigned to the Target Complete milestone with a Constraint Date of 1/27/23. Based on the MFO, the top path has 6 days of Total Slack and the bottom path has 4 days of Total Slack.
Following are examples of how the schedule is calculated, depending on whether that date is earlier than the Finish (Early Finish) date, later than the Late Finish date, or in between the two dates (EF and LF) for that milestone.
For these examples we are changing the Deadline date. In your actual project, the same effects will occur if the calculated milestone dates change due to schedule progress or schedule modifications.
First, we will look at the effect of a Deadline that is earlier than the Finish (Early Finish) date of the milestone, by assigning a Deadline date of 1/13/23.
The backward pass is recalculated starting at that milestone. The Deadline is earlier than the Late Finish date, so the backward pass is calculated using that date (the earliest late date).
The Deadline date drives the backward pass to be earlier than the forward pass so the Total Slack is negative and the warning indicator is shown for the milestone.
The backward pass is again recalculated starting at that milestone. The Deadline is earlier than the Late Finish date, so the backward pass is calculated using that date (the earliest late date).
The date drives the backward pass to earlier dates than before (with no Deadline), so the Total Slack for that path is recalculated, and reduced from its original value of 6 days to 3 days. This reflects the requirement to be done on 1/20/23.
The backward pass is not recalculated because the Deadline is later than the Late Finish date, so the backward pass is calculated using existing Late Finish date (the earliest late date).