# Dependencies & Predecessor Dates

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edited 12/09/19

Hello,

I am having trouble with predecessor dates.   I would like the duration and dates to be set automatically for line 10 as Rows 9 and Rows 17 change to accommodate variables.  I'd like the date to load as one day after the Finish Date of row 9, and end one day before the begin date of row 17.  It isn't working out that way.  Can someone please explain my error in thinking?

I used the predecessor setting 9FS+1d, 17SF+1d

Thank you!

• Employee
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Hello,

Thanks for your post, I'm happy to assist with your predecessors. First, take a look at my response to this other Community Post which clarifies how tasks with multiple predecessors will function: https://community.smartsheet.com/discussion/double-dependencies

To expand on the above, predecessors can only be used to automate either the Start or the End of the dependent task, but they are unable to automate the duration (IE both Start & End) of a task.

When a task has multiple predecessors, the respective dates of that task will adopt the dependency that delays the task most. Here's the breakdown of your current setup:

• Dependent Task - 1d Duration, 9FS, 17SF
• The time frame of the dependent task depends on two things: the start may rely on the end of task 9, or the end may rely on the start of task 17.
• If the end of task 9 is March 3rd, then the start of the dependent task would be March 4th. Since it has a duration of 1d, the end of the dependent task would be March 5th
• If the start of task 17 is March 8th, then the end of the dependent task would be March 7th. Since it has a duration of 1d, the start of the dependent task would be March 6th.
• Since the dependency on task 17 causes the task to occur later (IE Start on March 6th rather than March 4th as it would with Task 9), this is the predecessor that the task will honor.
• If the end of Task 9 is pushed later than March 6th, causing the start of the dependent task to be March 7th, then this is the predecessor that the task will honor because it causes the dependent task to start later (On March 7th rather than March 6th)

There isn't really a way to automate the duration of tasks in a Smartsheet project, but please feel free to submit a product enhancement request with the quick link to the right. One thing that you may consider is using only a single predecessor, 9FS, then in another cell, enter a formula to calculate the duration between the end of Task 9 and the start of Task 17. An example formula is as follows: =NETWORKDAY(\$[End Date]\$9, \$[Start Date]\$17)

Note that the above formula cannot be entered directly into the duration column, so you'll still need to manually enter it after the formula is calculated, but it will be much easier to do with the automatic calculation clearly visible.

Here are some resources related to the above:

I hope this helps!

Isaac J

Smartsheet Support