One of the most common questions I hear from project managers is: How do I determine how long a project should take?

Many project managers use the old-fashioned gut check method, in which they rely on past experiences to guess how long it will take to complete a task. While this method may occasionally work for smaller projects, it becomes more difficult to accurately execute as the project grows in size and complexity.

The following methods can guide you in determining your project schedules with a higher degree of accuracy and help your organization efficiently plan and track projects.

Activity definition

Activity definition is when you break down a project into the individual tasks that are necessary to produce the project’s deliverables. By using methods such as Organizational Process Assets, Enterprise Environmental Factors, Work Breakdown Structure, and the Project Scope statement in your project management plan, you can start defining the required activities.

There are many ways to go about this, but I tend to use process decomposition; it allows me to break down each element of the work packages into a scheduled activity by team member based on who is responsible for the package. At this point, you can also create the activity lists, which help define what needs to be done later.

Activity sequencing

Activity sequencing is when you decide the order in which the project’s activities need to be completed. Two common methods for doing activity sequencing are the Arrow Diagramming Method and the Precedence Diagramming Method. I find the Precedence Diagramming Method more flexible for my projects, but I recommend that you assess the pros and cons of both methods to see which one works best for your projects.

Activity duration estimation

Many factors contribute to determining a project’s activity duration; these factors may include business needs or situations that have legal requirements.

To estimate an activity’s duration, start by using your Project Scope statement in order to understand any project constraints or assumptions that could impact your estimating. You can base your estimates on similar activities that have occurred in the past (analogous estimating), or you can estimate based on how long something typically takes to accomplish (parametric estimating). An example of a parametric estimate is: If it takes two weeks to build one house, it will take six weeks to build three houses.

You can also estimate an activity’s duration by using the Program Evaluation and Review Technique (PERT) formula. PERT weighs the average of the pessimistic (P), most likely (M), and optimistic (O) estimates for an activity. For example:

PERT formula = (P+4M+O) / 6

Activity resource estimating

Once you know which tasks to complete, it’s time to figure out: how many resources you need, when you need the resources during the project, and how long you will need the resources.

You shouldn’t need to do much guessing because you can rely upon your Organizational Process Assets, expert judgment, published existing data, or bottom-up estimating when validating your resource requirements. All of these methods are valid ways to put firm numbers in place when determining your resource needs.

Schedule development

During schedule development, you bring together information from activity sequencing, activity duration estimation, and activity resource estimating to help build your project schedule, as well as your project schedule baseline.

If there are any issues at this point in your schedule, you can perform resource leveling or schedule compression. Resource leveling will help you manage your resources during periods where you may have initially found them to be over/under committed. Schedule compression will show you the impact of adding more resources to any critical path items or how running tasks in parallel can benefit the schedule.

Schedule control

While schedule control is part of the necessary Integrated Change Control process, you must also know where your project is at any point in time. This step will help you define and communicate how to handle things that affect the project’s timelines. Any changes that may impact areas such as the schedule baseline or approved change requests need to be handled via this process to ensure you can track their significance on the project.


During the course of any project, you will struggle with questions about what to do and when to do it. By taking a more structured approach when defining and answering your questions about time management, you will put yourself in a better position to come away with a plan that you can explain and execute.

Bill Stronge is a PMP certified Project Manager with a Global CPG organization currently focusing on eBusiness projects. During his 14+ years, he has worked on enterprise-wide applications in both a developer and architect role, as well as a project manager leading teams of various sizes. He can be reached for questions at


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