Start Date, Finish Date, and Duration Relationships

Start Date, Finish Date, and Duration are all interrelated and a change in one may dynamically affect the others on the same task as well as other tasks. Within a task, the Start Date, Finish Date and Duration must always remain in sync such that:

  • Finish Date is greater than or equal to Start Date (must be working days)
  • Duration = (Finish Date – Start Date + 1) – Nonworking Days
 

Note: If the task starts and ends on the same day, the Duration is one (1) day.

Additionally, the Start and Finish Dates and Duration of parent tasks cannot be edited. The Start Date of a parent task always remains equal to the earliest Start Date across all its subtasks. Likewise, the Finish Date always remains equal to the latest Finish Date across all its subtasks. The Finish Date must always be greater or equal to the Start Date, which would make the value for Duration greater than or equal to one (1) as well.

Actions that result in an update of one of the values results in changes in Start Date, Finish Date, and / or Duration on a task. The project task Scheduling Preference is examined when changes are made directly to Start or Finish dates to determine what takes priority when making adjustments to keep Start Date, Finish Date, and Duration in sync. For more information, see Scheduling Preference.

Dependencies

Dependencies allow start and finish dates of Successor tasks to automatically adjust as Predecessor task start and / or finish dates are changed. This allows the project plan to accommodate changes while preserving the relationship between tasks.

Setting Dependencies

Dependencies can be set by:

  • Clicking on the Source Task (Predecessor) and dragging to the Target Task (Successor) on the Gantt Chart. This creates Finish-to-Start dependencies with no lag.
  • Typing task line numbers and optional Lag directly on the grid in the Predecessors or Successors columns
  • Selecting two or more tasks and selecting the Link option from the right-click context menu options. This creates Finish-to-Start dependencies with no lag.

When dependencies are set, the start date of the task is set to the latest finish date of all of predecessors + 1 day. This is adjusted plus / minus (+/-) based on any specified lag. The start date is then adjusted forward to accommodate any applicable work calendar and associated exceptions to ensure the start date falls on a working day. The finish date is then adjusted to accommodate a fixed duration of the task, for example, the same duration as before the dependency applied.

If dependencies are broken, the Start Dates of Successor tasks should remain fixed as previously set by the dependency.

Dependency Rules

The following rules apply for setting dependencies:

  • A task cannot have a Successor set for which it is already a Predecessor
  • A task cannot have a Predecessor set for which it is already a Successor
  • A task cannot be linked to a task which indirectly links back to the task
  • Tasks cannot be linked in a way that leads back to the first task
  • A task cannot be linked to its parent

  • A task cannot be linked to its child

If a validation fails and the requested dependency created a change to either the Predecessor or Successor columns, the Predecessor and Successor columns revert to their entries immediately prior to the invalid request.

The resulting dependencies that are validated and created have:

  • One or more Finish to Start dependencies
  • The Start Date and Finish Date of the task adjusted
  • An arrow drawn on the Gantt Chart from the Source Task to the Target Task

  • Predecessor and Successor columns in sync. For example, if line 6 has a Predecessor set to 3, then line 3 will have a Successor set to 6.

  • Two parent tasks that are linked and create an implied dependency on the children of the second task

Updating DEPENDENCIES

Dependencies may be updated by:

  • Typing task line numbers and optional Lag directly on the grid in the Predecessors or Successors columns
  • Adding / moving / deleting lines using the right -click context menu options. The new ordering or rows results in adjustments to the current order and updates to the line numbers of any other reordered rows.
 

Note: Any Predecessors and Successors referencing updated line numbers will need to be updated to reflect the updated line numbers.

REMOVING DEPENDENCIES

Dependencies may be removed by:

  • Right-clicking on the dependency in the Gantt Chart on the arrow and selecting Delete
  • Deleting line numbers in the grid from the Predecessor and / or Successor columns
  • Selecting one or more tasks in the grid and then using the Unlink option from the context menu
 

Note: Selecting one task to unlink removes all links from the task as well as the links on the associated tasks.

When a Predecessor is deleted from one task, this results in the Successor also being deleted from the related task.