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About Task Dependency Relationships and Lag

In Project Task Gantt you can create a task dependency relationshipA relationship between two tasks. If a task is completed early or late, this has an effect on the start and end date of the task that succeeds it. between two tasks using dependency types. You can also specify a lagThis term is either a delay or an overlap between tasks in a dependency relationship. According to the dependency type, lag is added (or subtracted when a negative value) to the start or end time of the successor task. time on a task dependency relationship.

Note:

Note

When you create a task dependency relationship in Project Task Gantt, the default lagThis term is either a delay or an overlap between tasks in a dependency relationship. According to the dependency type, lag is added (or subtracted when a negative value) to the start or end time of the successor task. time of 0 is applied. When you change the dates of a dependent task, for example by dragging the task bar on the Schedule pane, the preceding task's dates are not updated in accordance with dependency rules.

To re-apply dependency rules:

• Right-click a task and select Apply Dependency Rules.
• Click Resolve Dependencies.

When you save changes dependency rules are not re-applied.

You cannot create a dependency relationship between a parent task and any other task.

Task Dependency Relationship Types

There are several types of dependency relationships that you can apply between two tasks. The first task in the relationship is known as the predecessor and the second called the successor. Dependency types and descriptions are provided here:

When a dependency is created between two tasks, the successor task's details are recalculated according to the dependency type you apply. The recalculation is also influenced by which duration unit each task is set to. The predecessor task does not move unless you manually change its details. When there are more than two tasks in a dependency, the predecessor task's details are recalculated appropriately when it is also a successor to another predecessor task.

Successor Task Recalculation Examples

We've provided some examples here to explain the recalculation of a task's details when it becomes the successor in the relationship depending on:

• The dependency type applied between two project tasks.
• Combinations of hours and days duration units set for tasks.

Successor Task Dependency Recalculations with Both Tasks in Days Examples

These examples show the recalculation of the successor task when both tasks are in duration units of days.

Predecessor		Successor		Dependency Type Applied	Recalculated Successor
Mon 01/01	9am - 5pm	Wed 03/01	9am - 5pm	Start to Start	Mon 01/01	9am - 5pm
Mon 01/01	9am - 5pm	Tue 02/01	9am - 5pm	Finish to Finish	Mon 01/12	9am - 5pm
Mon 01/01	9am - 5pm	Wed 03/01	9am - 5pm	Finish to Start	Tue 02/01	9am - 5pm
Mon 01/01	9am - 5pm	Tue 01/01	9am - 5pm	Start to Finish	Fri 29/12	9am - 5pm

Successor Task Dependency Recalculations with Predecessor Task in Days and Successor Task in Hours Examples

These examples show the recalculation of the successor task when the predecessor is in the duration unit of days and the successor task is in hours.

Predecessor		Successor		Dependency Type Applied	Recalculated Successor
Mon 01/01	9am - 5pm	Mon 01/01	11am - 3pm	Start to Start	Mon 01/01	9am - 1pm
Mon 01/01	9am - 5pm	Mon 01/01	7am - 2pm	Start to Start	Mon 01/12	9am - 4pm
Mon 01/01	9am - 5pm	Mon 01/01	11am - 6pm	Finish to Finish	Mon 01/01	10am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	8am - 3pm	Finish to Finish	Mon 01/01	10am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	11pm - 3am	Finish to Start	Mon 01/01	5pm - 9pm
Mon 01/01	9am - 5pm	Mon 01/01	7am - 2pm	Finish to Start	Mon 01/01	5pm - 12am
Mon 01/01	9am - 5pm	Mon 01/01	7am - 2pm	Start to Finish	Mon 01/01	2am - 9am
Mon 01/01	9am - 5pm	Mon 01/01	3am - 7am	Start to Finish	Mon 01/01	5am - 9am
Mon 01/01	9am - 5pm	Mon 01/01	7pm - 2am	Start to Finish	Mon 01/01	2am - 9am

Successor Task Dependency Recalculations with Predecessor Task in Hours and Successor Task in Days Examples

These examples show the recalculation of the successor task when the predecessor is in the duration unit of hours and the successor task is in days.

Predecessor		Successor		Dependency Type Applied	Recalculated Successor
Mon 01/01	11am - 3pm	Mon 01/01	9am - 5pm	Start to Start	Tue 02/01	9am - 5pm
Mon 01/01	7am - 2pm	Mon 01/01	9am - 5pm	Start to Start	Mon 01/01	9am - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	9am - 5pm	Finish to Finish	Mon 01/01	9am - 5pm
Mon 01/01	11am - 6pm	Mon 01/01	9am - 5pm	Finish to Finish	Tue 02/01	9am - 5pm
Mon 01/01	2am - 7am	Mon 01/01	9am - 5pm	Finish to Start	Mon 01/01	9am - 5pm
Mon 01/01	7am - 2pm	Mon 01/01	9am - 5pm	Finish to Start	Tue 02/01	9am - 5pm
Mon 01/01	7am - 2pm	Mon 01/01	9am - 5pm	Start to Finish	Fri 29/12	9am - 5pm
Mon 01/01	7pm - 2am	Mon 01/01	9am - 5pm	Start to Finish	Mon 01/01	9am - 5pm

Successor Task Dependency Recalculations with Both Tasks in Hours Examples

These examples show the recalculation of the successor task when both tasks are in the duration unit of hours.

Predecessor		Successor		Dependency Type Applied	Recalculated Successor
Mon 01/01	7am - 2pm	Mon 01/01	11am - 3pm	Start to Start	Mon 01/01	7am - 11am
Mon 01/01	11am - 3pm	Mon 01/01	7am - 2pm	Start to Start	Mon 01/01	11am - 6pm
Mon 01/01	11am - 3pm	Mon 01/01	9am - 5pm	Finish to Finish	Mon 01/01	7am - 3pm
Mon 01/01	11am - 3pm	Mon 01/01	7am - 2pm	Finish to Finish	Mon 01/01	8am - 3pm
Mon 01/01	7am - 2pm	Mon 01/01	4pm - 10pm	Finish to Start	Mon 01/01	2pm - 8pm
Mon 01/01	7am - 2pm	Mon 01/01	11am - 3pm	Finish to Start	Mon 01/01	2pm - 6pm
Mon 01/01	7am - 2pm	Mon 01/01	11am - 3pm	Start to Finish	Mon 01/01	3am - 7am
Mon 01/01	7pm - 2am	Mon 01/01	11am - 3pm	Start to Finish	Mon 01/01	3pm - 7pm

About Lag Time on Task Dependency Relationships

Lag can be applied when there is a dependency relationship between two project tasks. The lag is the time gap added or subtracted from the end of a predecessor task before the successor task can start. The default lag is 0. Lag time can be a positive or negative value. For more information, see the description for the Lag field.

Formulas recalculate project task start or end dates and times accordingly in dependencies when you update the dependency’s lag time.

Lag Formula Examples

We've provided some examples to explain recalculation of the successor task's details according to the lag you apply to your dependencies.

Finish to Start Lag Formula Examples

Predecessor		Successor		Successor Duration Unit	Lag Time Applied	Recalculated Successor With Lag
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2d	Thur 04/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2d	Fri 28/12	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2h	Mon 01/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2h	Mon 01/01	9am - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2d	Wed 03/01	3pm - 9pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2d	Sat 30/12	3pm - 9pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2h	Mon 01/01	5pm - 11pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2h	Mon 01/01	1pm - 7pm

Start to Finish Lag Formula Examples

Predecessor		Successor		Successor Duration Unit	Lag Time Applied	Recalculated Successor With Lag
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2d	Tue 03/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2d	Wed 28/12	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2h	Mon 01/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2h	Mon 01/01	9am - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2d	Wed 03/01	5am - 11am
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2d	Sat 30/12	5am - 11am
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2h	Mon 01/01	7am - 1pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2h	Mon 01/01	3am - 9am

Start to Start Lag Formula Examples

Predecessor		Successor		Successor Duration Unit	Lag Time Applied	Recalculated Successor With Lag
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2d	Wed 03/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2d	Thur 28/12	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2h	Mon 01/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2h	Mon 01/01	9am - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2d	Wed 03/01	11am - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2d	Sat 30/12	11am - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2h	Mon 01/01	1pm - 7pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2h	Mon 01/01	9am - 3pm

Finish to Finish Lag Formula Examples

Predecessor		Successor		Successor Duration Unit	Lag Time Applied	Recalculated Successor With Lag
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2d	Wed 03/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2d	Thur 28/12	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	2h	Mon 01/01	9am - 5pm
Mon 01/01	9am - 5pm	Mon 01/01	9am - 5pm	Days	-2h	Mon 01/01	9am - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2d	Wed 03/01	9am - 3pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2d	Sat 30/12	9am - 3pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	2h	Mon 01/01	11pm - 5pm
Mon 01/01	11am - 3pm	Mon 01/01	10am - 4pm	Hours	-2h	Mon 01/01	7am - 1pm

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