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Scheduling from constraint date when the constraint date is half way through the

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  • #413251 Reply
    Julie Trask

    I need to schedule a project that half way through has a constraint that cannot finish past a certain date. All the tasks above that date need to schedule backwards from that date and after the constraint date, tasks can schedule as normal, finish to start. What is the best way of doing this eg scheduling the first half of the project so it schedules from the constraint date backwards.

    #413252 Reply
    Sai Prasad
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    In Project tab > Project Information, you can choose either forward or backward schedule (Schedule From:) for the entire project; not for the portion of the plan. My suggestion is you choose Schedule From: as Project Start Date, and insert a milestone task midway in the plan. On that milestone, set the deadline (Task Information > Advanced) rather than constraint type as Finish No Later Than. Former option gives you alert in the Indicator column that the milestone is missed and you can compress the schedule to recover, but the latter option will create a schedule a conflict and the schedule will not be achievable.

    #413254 Reply

    Adding to Sai’s comments. For the first half of the schedule, you can set the task Constraint Type to As Late As Possible on all tasks. While still scheduling from the start date forward, the tool will schedule these tasks to occur as late as possible based on dependency relationships. So all first half tasks would be pushed as close to the central constraint date as possible. If the constraint date moved either way, these first half tasks would also move accordingly.
    I’ve done this on a limited basis within my schedule and it seems to work well. I’ve never done it with half the schedule.
    It would also be easy to test once the schedule is constructed.
    First, construct the schedule as you normally would with all the dependencies on all tasks. Add the constraint type column to a task oriented view, set the first task constraint type to As Late As Possible, scroll down to the last task before the constraint, shift click in the Constraint Type column (must be that column), right click in the shaded rows, click Fill Down and the tool will change all highlighted tasks to your desired constraint type as set by the first highlighted row. Then level and check the results.

    #413255 Reply
    Heather Agee

    While the tool will allow you to schedule backwards, there are many reasons why this is not a good methodology. Scheduling backwards using either the “Schedule from Finish Date” or “As Late as Possible” methods is very risky. Basically you will be driving the start date of each task off of the latest finish date and the duration of the task, which means you will wait to start the task until the latest start date possible…and therefore any slip to any task in the schedule is a day for day slip to the project. A better method, in my opinion, is to schedule everything as soon as possible, from the start date of the project. Then put your milestone in with a deadline set for the date you need to hit. This way, your schedule can still move properly left or right with you starting everything on the early start date when possible, but MS Project will warn you when you have breached the deadline that you set on that task. It would probably also be a good idea to baseline that milestone for the date you want to hit so you can watch your finish variance to make sure you stay on your baseline date.

    #413256 Reply
    Larry Christofaro

    I agree with Sai and especially Heather. But to follow up with Daryl’s idea, you could give backward scheduling / as late as possible a test and determine if it provides a value. If it does, set one of your baselines, then resort back to a forward schedule. That baseline could give you valuable information on where you are to your deadline. Hmmm, on another thought, you could also use Free Slack / Total slack and Late Start to determine how much contingency you have to your deadline. You could even setup a special Gantt format that uses Late Start / Late Finish. Anyway, some additional thoughts to try and see if something works for you. Project usually has multiple options and lets the user figure out what option has the best effort / value. Good luck…

    #413257 Reply

    I agree with Heather’s comments. Backwards scheduling and as late as possible add risk because your are telling the tool to schedule each task to start at the last possible moment without impacting the constraint date in the middle of your schedule (or project end). So rather than saying Bob can start task A now because he’s available and all predecessors have been met, the tool may tell Bob not to start task A until 2-3 weeks from now, effectively eliminating all available slack.
    I think the driving question is what you as the PM are trying to achieve.
    Are you simply trying to find out the latest possible project start date. If that’s the case, use the backwards scheduling/as late as possible technique to determine the latest possible start date. Once that’s determined schedule and manage the project as normal using forward pass/as soon as possible.
    If you’re trying to figure out where the constraint date should be set, you can follow Heather’s comments, and the critical path will tell you where to set the milestone constraint date. You can also experiment with changing project start dates and rescheduling to determine a latest possible start date.
    If you plan to manage the schedule with the backward pass/as late as possible configuration, be aware of the risks introduced and understand that every task is now scheduled to start at the last possible moment and there will be basically zero slack.

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