Triple Constraint Theory in Project Management

What is triple constraint theory in project management?

The triple constraint theory may sound complicated, but it’s really pretty simple.

Let’s start with a definition. The triple constraint theory in project management says every project operates within the boundaries of scope, time, and cost. A change in one factor will invariably affect the other two.

For example, if a client wants to add a bunch of new features to the project’s scope, they’ll have to budget more time and money to get ‘er done. Or if your boss slashes your project budget, you’ll need to scale back the project requirements.

In other words, it’s all about trade-offs. As project manager, it’s your job to balance these triple constraints and manage expectations so everyone understands what it takes to achieve project success.

The project management triangle

The triple constraint theory is often referred to as the project management triangle. Each side or point of the triangle represents the triple constraints of project management: scope, time, and cost.

Let’s dig a little deeper into each project constraint.

Triple constraint: Scope

Scope creep has a funny way of sneaking up on you. Before you know it, “just one more thing” has turned into a completely different project deliverable.

That’s why it’s important to define—and document—project goals and requirements before work begins. That way everyone knows what “done” looks like, and you have a project truth to refer back to if the scope starts to creep.  

Adding more features can stretch a project’s time and budget constraints. You’ll either need to extend the deadline or assign more people to the work, increasing project costs. Monitoring scope changes enables you to discuss trade-offs early and make necessary adjustments before your project gets off course.

Triple constraint: Time (schedule)

In project management, most folks know, if you want a project done fast, it’s gonna cost you—especially if you’re not willing to bend on the scope. That’s because a short deadline requires more resources to get the work done on time.

A detailed scope document provides the perfect foundation for understanding your project’s time constraint because you can use it to build out a project estimate. Be sure to bring your team into the discussion and look beyond task hours. The time you spend in meetings or holding a stakeholder’s hand through the process counts too.

The more accurate your estimate, the better. After all, it’s what you’ll use to schedule work and drive project decisions if tough choices need to be made to meet the project deadline.

Triple constraint: Cost (budget)

Estimating a project’s time and effort also forms the basis for your project budget. Here are a few costs to consider when formulating a project budget:

• Resource costs, based on estimated hours (or story points in Agile)
• Materials
• Equipment
  

When it comes to budget constraints, remember, it’s best to communicate early and often. No one likes being surprised by a big bill (or the tense conversation that inevitably follows).

If an unexpected expense pops up, take time to explain how it will impact the rest of your project, and let your client decide whether or not it’s worth the extra dough. Your client isn’t a project expert and may not realize how much that shiny new feature will cost them in the end.