Understanding the basics of a project development schedule

The two main components of a project development schedule (aka project programme) are activities and milestones. These can be tracked in a couple of important aspects: dates, and completion status. In this article, we will take a deep dive into the details and explain how it all works.

Project Development Schedule

Activities and Milestones are the two key components in a schedule.


Activities can be interpreted as "tasks" that need to be completed in order for a project to be finalized. An activity will always have a start and end dates. For these dates, the following are date types that need to be tracked

  • planned dates, are the original approved plan that the team has agreed upon
  • forecast dates, new plan dates based on recent developments
  • actual dates, are the real dates that the activity started and finished

The level of detail an activity (and the schedule) has will depend on the intended use.

A very granular and specific schedule is typically intended for a team that is working with it on a day-to-day basis such as an onsite team executing a certain scope of work. On the other hand, a high-level schedule that provides a general overview is used for strategic and informative purposes; this is the schedule type a stakeholder (such as a project owner, financier, tenant) can benefit of.

The beauty of a well managed schedule is that a granular and high-level schedule can be derived from the same master schedule. This is possible thanks to concept of hierarchies, which is formally called work breakdown structure (WBS). You can think of a WBS as nesting activities in different layers and rolling them up into groups, also known as levels. A typical granular schedule has up to 5 levels of detail.

An activity can have a few additional key characteristics that are important for schedule development purpose, such as total float (when total float is zero, it means the activity is part of the critical path), logic ties, sequencing and more. Reviewing these characteristics is a topic of its own and will be discussed on a separate blog post.

Completion status

A completion status is used to measure the completeness of an activity and its tracked in percentage. The percent of completion for an activity can be defined in many ways and its up to the project management team to establish this criteria. The typical definition for it, is the completion of the deliverable from a scope of work perspective (e.g. physical progress). For instance, if the activity is to install 100 meters of pipe and the team in charge has currently installed 60 meters, the completion status for that activity is 60%.

The percent complete bring a perspective to the activity progress status since it helps reflect a more accurate completion date estimate.


A milestone is a single-date event that is of relevance for the project as it moves forward towards the overall completion. For the most part, a milestone is linked and depends to a preceding activity that marks that milestone's date. A milestone will also have the different date types: planned, forecast and actual. Since a milestone doesn't have a start and end date, there is no wya to track completion status of it.


This article highlights the basics of a project development schedule, to help anyone that has a schedule in their hands and make sense of it. Activities (and their levels), milestones and completion status covers what should matter the most to a construction project stakeholder.

Written By
Pablo R.