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Understanding Milestone Dates & Their Relationship with the Gantt Chart

This article explains how Milestone dates work in PM3 and how they interact with the Gantt Chart. It is intended to help end users understand which dates they can edit, how those dates behave at different workflow stages, and how updates are reflected across the system.

Understanding Milestone Dates & Their Relationship with the Gantt Chart

This article explains how Milestone dates work in PM3 and how they interact with the Gantt Chart. It is intended to help end users understand which dates they can edit, how those dates behave at different workflow stages, and how updates are reflected across the system.

Terminology

  • Milestone: A Milestone represents a single point in time. It has no duration and therefore no start or end date.

  • Task: A Task has both a start date and an end date, and therefore has a duration.

    Note: Milestones always appear on both the Milestone Page and the Gantt Chart, and updates can be made from either location.

Milestone Dates on the Milestone Page

Each Milestone can contain several different date fields, each serving a specific purpose.

Planned Date

  • The date the Milestone is expected to be completed during initial project planning.

  • Can be edited multiple times while the plan is in Workflow Stage 1 or 2.

  • There is no history of Planned Dates. Updating the date overwrites the previous value.

  • Once the plan enters Workflow Stage 3, the Planned Date is baselined and locked.

  • PM3 Admins can revert the plan back to Workflow Stage 2 if a Planned Date must be changed after baselining.

Revised Date

  • Represents the current expected completion date after the plan has been baselined.

  • Can be entered or updated at any time, in any workflow stage.

  • Allows visibility of:

    1. The original baselined date (Planned Date)

    2. The current delivery expectation (Revised Date)

  • Can be populated even if no Planned Date exists.

Completed Date

  • The date the Milestone was actually completed.

  • Can be entered or updated at any time.

  • May be before or after the Planned Date or Revised Date (if present).

  • Can be entered even if no Planned or Revised Date exists.

Merged Date (Calculated)

  • A system-calculated date that cannot be manually edited.

  • Used primarily to sort Milestones into a logical chronological order.

The Merged Date is calculated as follows:

  1. If a Completed Date exists → Merged Date = Completed Date

  2. Else if a Revised Date exists → Merged Date = Revised Date

  3. Else if a Planned Date exists → Merged Date = Planned Date

  4. If none of the above exist → Merged Date is blank

Milestones on the Gantt Chart

The Gantt Chart can display Tasks, Summary Tasks, and Milestones. Milestones created or updated on the Milestone Page are automatically shown on the Gantt Chart, and changes made on either page stay fully synchronised.

Gantt Chart Date Fields for Milestones

Because the Gantt Chart supports both Tasks and Milestones, it includes some date fields that do not appear on the Milestone Page.

  • Start Date: For Milestones, the Start Date is non-editable. It is always the same as the Estimated Finish date.

  • Estimated Finish: This date determines where the Milestone appears on the Gantt Chart timeline.

    • Represents the current expected completion date.

    • Can be edited directly in all workflow stages.

    • Always matches the Merged Date for the Milestone.

What happens when you edit the Estimated Finish?

The system updates different fields based on the current data and workflow stage:

Scenario Workflow Stage Resulting Action
Planned Date exists, No Revised/Completed Date Stage 1–2 Planned Date is updated
Planned Date exists, No Revised/Completed Date Stage 3+ Revised Date is updated
Revised Date exists, No Completed Date Any Revised Date is updated
Completed Date exists Any Completed Date is updated

Additional Gantt Fields

Revised Date (on the Gantt)

  • Identical to the Revised Date on the Milestone Page.

  • Updating it on the Gantt also updates it on the Milestone Page.

  • If no Completed Date exists, updating the Revised Date will also update:

    • Estimated Finish

    • Start Date (always aligned to Estimated Finish)

Completion Date (on the Gantt)

  • Identical to the Completed Date on the Milestone Page.

  • Updating it on the Gantt also updates it on the Milestone Page.

  • Updating the Completion Date will also update:

    • Estimated Finish

    • Start Date (always aligned to Estimated Finish)

Merged Date (on the Gantt)

  • Fully calculated and never editable.

  • Follows the same calculation rules as the Merged Date on the Milestone Page.

Key Takeaways

  • Milestones are single points in time with no duration.

  • Planned Dates are locked once a plan is baselined (Workflow Stage 3).

  • Revised Dates allow ongoing schedule updates without losing the original baseline.

  • The Gantt Chart and Milestone Page are fully synchronised.

  • The Merged Date always determines where a Milestone appears on the Gantt Chart.

Understanding how these dates interact will help you confidently manage schedules while preserving clear baseline and delivery expectations.