Have you ever been unable to change the start date of a task in Microsoft Project? You type in 11/2 for the start date and it changes back to 11/19. In most cases, Project is not misbehaving; you need to understand what Project assumes when it schedules tasks. In this series, we’ll explore how Project’s scheduling algorithms use links, constraints, preset options, and dates to automatically set your task start and finish dates.
Part 1 of 3 introduces the topic and covers the first two considerations to keep in mind regarding MS Project’s scheduling priorities.
One of the strengths of automated project management tools is their ability to apply some basic project management concepts. For example, if a predecessor task finishes late, Project moves the successor (linked) task to a later date for you. While such automated scheduling features are usually helpful, mastering them requires a complete understanding of how they are designed to work.
If you try to link a task or change the date of a task and MS Project doesn’t cooperate, there are several justifications Project may have for insisting on certain dates. The key is to understand the sense behind Project’s priorities when setting task dates. The main considerations to make are listed below:
- How does the Project Start Date affect a Task Start Date? (covered in this article)
- How can a Task Date Constraint affect a Task Start Date? (covered in this article)
- How do Task Links override a date that I enter? (to be covered in Part 2)
- How do Linked Summary Tasks affect my ability to set a task date? (Part 2)
- How does an Actual Start Date affect a linked task? (Part 2)
- How can setting calculate to manual affect my task dates? (Part 3)
- How do calendars affect the schedule calculation? (Part 3)
- How does Resource Leveling affect the schedule calculation? (Part 3)
Project provides a lot of help to spot these potential problems. To make sure Project is able to help you spot these problems, it’s a good idea to preset a couple of options in your plan.
The first of these is the Show scheduling messages option. This option is selected by default, but you can make sure that it’s set in the Project Options dialog box by going to File:Options. The Show scheduling messages option box is under Schedule:Schedule; make sure that it’s ticked, as in Figure 1.
The other helpful feature is the Planning Wizard, which is also on by default. To ensure that all of the Planning Wizard options are set, go to the Project Options dialog, then go to Advanced:Planning Wizard and confirm that all of the option boxes are checked.
Enlisting Help from Task Inspector
The Task Inspector can be launched from the Task:Tasks tab in the ribbon, by clicking the Inspect button (or by clicking on the drop-down arrow next to Inspect and selecting Inspect Task). As seen in Figure 3, a pane appears on the left side of your screen showing the reasons why a Task Start Date may have the value it does. This series covers several of the tests carried out by the inspector as well as several extra factors that come into play so that you do not have to use the inspector every time.
Consideration #1: How does the Project Start Date affect a Task Start Date?
If there are no other scheduling influences at work, a task will be scheduled to start on the Project Start Date. You can see this at work when all the new tasks line up to start on the same date as you enter them in. You should always be aware of what your Project Start Date is and be ready for the effect on your schedule. If you change the Project Start Date using the Project Information dialog box (found under Project:Properties:Project Information, as seen in Figure 4), then the dates of all tasks scheduled to start on the Project Start Date will change accordingly (as seen in Figure 5).
Consideration #2: How can a Task Date Constraint affect a Task Start Date?
Task constraints often make linking tasks and setting successor start dates a little confusing. If you key a start date for a task, Project will change the default constraint from As Soon As Possible (ASAP) to Start No Earlier Than (SNET) for the date you specified. Likewise, if you key a finish date for a task, Project will change the default constraint from As Soon As Possible (ASAP) to Finish No Earlier Than (FNET) for that date.
For an example of how the SNET constraint works, open a project file and highlight a task. Then, go to the Task Information dialog box by going to Task:Properties:Information in the ribbon. Once in the dialog, you can see–and change–the Constraint date under the Advanced tab.
When you specify date constraints, then the given task will have a calendar symbol in the Indicator column, as seen in Figure 6.
This constraint also affects your task links and successor start date. Figure 7 serves as an example of this. Task 24 has an SNET date of 11/26, and Task 23 (the predecessor) is linked to Task 24 (the successor) with a finish-to-start relationship. If Task 23 ends on 11/19, you might expect Task 24 to start on 11/20, but as Figure 7 illustrates, MS Project honors the Start No Earlier Than constraint and keeps Task 24 scheduled for 11/26.
The above figure shows what appears to be a 4-day lag between Tasks 23 and 24 even though the lag for these linked tasks shows that it is set to zero days (0d).
If you think a date or a link is acting strangely, then don’t give up. Project is doing what it was designed to do; you just need to hang in there and understand how Project deals with dates, links, and constraints as it schedules your tasks. Chances are pretty good that once you understand the mechanics behind it, you’ll agree with the automation.