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Schedule a Task to Start As Late As Possible Based on the Start Date of Another Task

Problem Description

I answered an interesting question recently in the Microsoft Answers user forum for Microsoft Project users. The user who asked the question stated that she was new to Microsoft Project. She indicated that she is managing a construction project and wanted to know the latest possible date she could order wood flooring so that it is delivered to the construction site just in time for the flooring to be installed.

Her situation with ordering the wood flooring is very similar to ordering the equipment for the Implement task, such as shown in Figure 1. Notice that the Start date of the Implement task is controlled by a series of Predecessor tasks, namely the Design, Build, and Test tasks. To match the situation faced by the user who asked the question in the forum, suppose that the Order Equipment task must start as late as possible and must finish immediately before the Implement task starts. This requirement is based on historical records that show it typically takes 5 days for new equipment to be delivered, once the equipment is ordered.

Figure 1: Order Equipment must start as late as possible

 

Solution

Although there are several possible solutions to this scheduling problem, the easiest way to solve the problem is to set an As Late As Possible (ALAP) constraint on the Order Equipment task. To do this, double-click the Order Equipment task and then click the Advanced tab in the Task Information dialog. Click the Constraint Type pick list and select the As Late As Possible constraint, such as shown in Figure 2. The behavior of this constraint is as the name implies: it schedules the task as late as it possible can, based on the task’s dependency relationships.

Figure 2 – Set an ALAP constraint on the task

 

Click the OK button when finished. Notice in Figure 3 that Microsoft Project schedules the Order Equipment task as late as possible, which means that it finishes immediately prior to the start of the Implement task. If the schedule slips on the Design, Build, or Test tasks, causing the Implement task to slip, the Order Equipment task will slip as well. This is the desired scheduling behavior for the Order Equipment task in Microsoft Project.

Figure 3: Order Equipment task scheduled as late as possible

 

Dale Howard
Written by Dale Howard

Dale Howard is the Director of Education for PROJILITY. He has used Microsoft Project since version 4.0 for Windows 95 and he has used the Microsoft PPM tool since the first version of released as Project Central in the year 2000. He is the co-author of 21 books on Microsoft Project, Project Server, and Project Online. He is currently one of only 28 Microsoft Project MVPs in the entire world and one of only 6 in the United States.

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3 Comments
  1. Thank you for this,however I think you should mention to this “novice” that in setting it to ALAP she’s removed all flexibility/float. My experience is that things rarely get delivered precisely on time. I would normally put a little bit of “fat” in the duration to allow for that. This is not just a software issue it is about project management and scheduling.

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  2. Suggest to limit/reduce the Order Equipment “duration” to 1d as ordering would not be require an action on Monday AND Tuesday AND Thursday …
    Since the 2nd factor is the delivery on-site delay after order takes typically 5 work days, wouldn’t it makes sense to add a condition in the Implement task that its predecessor task Order Equipment has a 5d delay Finish-Start?

    I can not follow Thomas’ comment, as either the 5d are a “safe” and “verified” delay between order and delivery on site or they are not – in which case I need to increase the 5d delay….

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  3. Thanks for the article Dale. This solution will work in this situation because the “Implement” task has no slack. Unfortunately, the way Microsoft has implemented the ALAP constraint, if there are successors to the ALAP task that have slack these too will be delayed which is rarely what the scheduler would like. Best to insure the ALAP constraint isn’t causing unintended consequences when using it!

    Reply

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