Understanding the Project Management Triple Constraint

Role of the Project Manager | By Duncan Haughey | Read time minutes

Colourful project management scope triangle reading - done quickly, high quality and low cost

Today, we carry out projects under certain constraints – traditionally, cost, time and scope. These three factors, commonly called the triple constraint, are represented with a triangle (see Figure 1). Each constraint forms the vertices and quality as the central theme:

  • Project managers must deliver projects within cost.
  • Project managers must deliver projects on time.
  • Projects must meet the agreed scope – no more, no less.
  • Projects must also meet customer quality expectations.
Project management triple constraint triangle with cost, scope, time, and quality in the centre
Figure 1. The Project Management Triple Constraint

Sometimes, a diamond replaces the triangle with cost, time, scope, and quality making up the four vertices and customer expectations as a central theme (see Figure 2). No two customer expectations are the same, so you must ask specific questions about the customer's expectations:

Project management quadruple constraint with cost, time, scope, quality, and expectations in the centre
Figure 2. The Project Management Quadruple Constraint

1. Cost: All projects have a finite budget; the customer is willing to spend a certain amount of money to deliver a new product or service. If you reduce the project's cost, you will need to reduce its scope or increase its time to delivery.

2. Time (Schedule): As the saying goes, time is money, a commodity that slips away too easily. Projects have a deadline date for delivery. When you reduce the project's time, you need to increase its cost or reduce its scope.

3. Scope: Many projects fail on this constraint because the project's scope is either not fully defined or understood from the start. When you increase a project's scope, you will either have to increase its cost or time.

Once a customer asks you to complete a project, the person will state what is necessary; for example, the project must cost no more than £50k to deliver by a particular date or contain certain product features.

The triple constraint is about balancing each constraint to reach a successful conclusion. As the project progresses, the project manager may find that any changes impact any of the constraints.

What might happen? Here are some examples:

1. During an automotive engineering project, your project receives an unexpected budget cut after the company posts poorer than expected 4th quarter financial results.

Impact: This leads to reduced project scope, reduced quality and a delay in the schedule to find more cost-effective resources. The most significant constraint, in this case, is the cost (the money the company is willing to spend).

2. During a project to create a new innovative mobile phone handset, your customer asks to bring the launch date forward two weeks to coincide with a major industry show.

Impact: Costs increase as the project manager adds more people to the project to meet the new deadline. Some product features are removed and put into a phase two release to reduce delivery time and meet the new launch date. The most significant constraint, in this case, is time (project schedule).

3. During a software development project, your customer, increases the scope. The customer asks for new software features after learning that a competitor's product will be in direct competition with their own. The product must include these new features if it is to compete successfully.

Impact: The budget and schedule increase as a result of pushing out the final delivery date. The project manager adds more people to the project to minimise disruption to the project schedule, thereby increasing the project's overall cost. The most significant constraint, in this case, is scope (features of the product).

In each of these examples, the project manager needs to rebalance the project to meet new constraints and deliver success for the customer.

The adage, Fast – cheap – good: You can have any two, has more than a grain of truth. Rarely do project managers find that they have the budget to deliver top quality on time. More often, a project manager needs to weigh one constraint against another to reach the best result.

As a project manager, you need to educate your customers about project management's triple constraint, create the best balance, and be aware of the changes that will impact cost, time, and scope.

The triple constraint represents vital elements of a project that, when balanced well, lead to success.

Recommended read: A Project Management Primer: Basic Principles - Scope Triangle by Nick Jenkins.


What's Next?

You may also be interested in