What is a milestone?

A milestone marks a project event, such as a need date or plan date, a delivery, the fact a (sub)-deliverable is ready, or as a start or finish for project events. A milestone should not be confused by a deadline.

Know the difference!

  • Milestone: marks when a project event WILL take place, based on project progress.
  • Deadline: marks when a project event SHOULD take place, based on (contractual) agreements with project stakeholders.
In the screenshot below you see several milestones. You can recognize a milestone in the Gantt Chart as a little black diamond. A milestone can be added via the tab Task > Milestone > name the milestone, or by entering the name of the milestone directly in the Task Name column and make the duration ‘0’. What is a milestone?1


In the screenshot above, deadlines have been added on the first four milestones (see little arrows pointing downwards in the Gantt Chart). You will learn more about deadlines in this post.


Milestones can slip while a deadline cannot (unless you make a new agreement with your stakeholder). Below you can see an example of a milestone that is too late for the agreed deadline. What is a milestone?3 lets us know if we are late or on time and how much slack we still have until the deadline (slack = the amount of time that a task or milestone in a project network can be delayed without causing a delay).

Watch here how to add a milestone

TIP: do not plan too many milestones as this induces a level of detail that is not necessary. Ask yourself if the project event is big enough to celebrate it.

Milestones as connection points

In a multi-project environment (or program) milestones can also be used as cross-project deliverables, thus acting as ‘connection points’ between schedules to indicate a delivery from or to another schedule. These milestones can be linked; this is described in Maturity Level 3 'Critical Path Management': link between projects. What is a milestone?2
Back to blog