Last edited 19 Jul 2021


Milestones are important project management tools that can be used as a component of project scheduling.

A milestone is a significant event that occurs during the course of a project, the timing of which can influence the scheduling of other activities. With the achievement of successive milestones, management is able to maintain a more accurate understanding of how the project is advancing according to the schedules.

Milestones might include, for example:

Milestones are a feature of many project management software tools and often appear on Gantt charts, represented by diamond symbols. Developing schedule with milestones marked along a project programme can help give clarity to a timeline which can otherwise be very complex and difficult to interpret. This can be particularly useful for some stakeholders who may only need a very general understanding of a project programme.

They may coincide with key decisions or gateways at which the client assesses the state of development of the project and considers whether to progress to the next stage. However, it is important that milestones are allocated to the achievement of a task, not to the task itself.

For example, consultants often describe client decisions as milestones on project programmes, when in fact, the client may need to be provided with information to make a decision, they need time to consider that information, and they may then need to convene a meeting, which if they are senior personnel may only be possible on specific dates (such as at pre-planned board meetings).

Milestones are known as a ‘task of zero duration’ because they represent a particular point of time in a project when an achievement has been reached, they do not represent the activities necessary to complete a task.

They are often used to show progress on critical rather than non-critical activities, that is, items that represent a potential ‘bottleneck’ in the progress of a project. The overall critical path for a project represents the shortest time in which the project can be completed. Achieving milestones on the critical path more quickly than was planned will reduce the overall project programme.

However, this can serve to present a misleading impression of the overall health of the project, as project managers may prioritise resources into achieving critical milestones, whilst neglecting those works that are not identified as a milestone. This can change the critical path so that activities which were not previously critical become so.

To be useful tools in monitoring and controlling a project, project managers must be careful not to overuse milestones as a means of driving progress, whilst ensuring there is no loss in momentum as a result of spacing milestones too far apart. Instead, a compromise must be reached with milestones pinpointing suitably critical deliverables on a consistent basis, commonly at intervals of no longer than every fortnight for projects of several months duration.

Suitable remedies must be planned in the event that a milestone is missed. Resources may need to be reallocated to ensure they continue to be matched to priorities. However, it is important that milestones represent a challenge and should be treated as opportunities to make adjustments as the work is proceeding.

See also: Milestone payment.

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