Start date depending on the duration and successor task

Hi there,

I have Task 1 and Task 2. Task 1 is predecessor of Task 2. Task 2 is a milestone set on a specific date.
I’d like Task 1 to have a flexible start date depending on its duration.

Example, if Task 2 is on Feb 1, 2020, and Task 1 takes 10 days, I’d like Task 1 start date calculated automatically 10 days prior. If I move Task 2 date, I’d like that Task 1 would move consequently.
Is it possible?

Thank you!

You may try replacing your dependency type from Finish-Start to Start-Finish and draw it backwards (from Task 2 to Task 1)

Hello Dmitry, thank you so much for you quick answer. Actually it doesn’t work. Start-Finish makes both tasks to start at the same time, as Task 2 is a milestone. I tried different options (FF, SS) or rubber link instead of strong, but it doesn’t work. It seems that the start and duration constraints of Task 1 always prevail. That should be a cool feature that I guess GanttProject doesn’t have yet. (or I didn’t find it).
Thank you anyway

It does work fine. See the attached project. You can move milestone and task_0 start date will change appropriately.

BackwardScheduling.gan (2.6 KB)

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Hello Dmitry, yes it does! I just applied the rule wrongly. My understanding was to add the rule to the milestone task, because in the milestone you define its predecessor, but the rule must apply on the task. Thank you so much for providing me with a sample, very useful, and thank you for your quick support.

Hi Dmitry and Rob, sorry to drag up an old post but I can’t find any other reference to this process.
I cannot duplicate this, it just adds a normal predecessor for me. Can either of you give a quick overview of how you did this. When I look at the task in Dmitry’s project I can see the arrow is pointing in the correct direction as does mine but it always pushes the prior task to be after task 2 instead of before. I am sure it must be something simple.

Knew I would find it after I posted. A normal predecessor is Finish-Start and placed on the second task. The reverse is as Rob mentioned, the predecessor is placed on the first but is set to Start-Finish as well.

My problem is setting the predecessor task to start a defined period before the start of the follow-on task - e.g. a payment milestone 6 weeks before delivery.

3 tasks.
Payment is a “milestone” type task, with “start-to-finish” tasks “payment period”, which has a “finish-to-finish” dependency to “delivery task”.

Does this work for you?