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Understanding the Project Management Triple Constraint

~ By Duncan Haughey

The words fast, cheap and good in coloured circles

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

  • Projects must be delivered within cost
  • Projects must be delivered on time
  • Projects must meet the agreed scope – no more, no less
  • Projects must also meet customer quality requirements
Project Management Triple Constraint Diagram
Figure 1. The Triple Constraint

More recently, the triangle has given way to a project management diamond: cost, time, scope, and quality are now the four vertices, with 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 Diamond Diagram
Figure 2. The Project Management Diamond

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

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 will either have to increase its cost or reduce its scope.

3. Scope: Many projects fail on this constraint because the scope of the project 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 important; for example, the project must cost no more than £50k, be delivered by a particular date, or contain certain 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 one or more of the constraints. What might happen? Here are some examples:

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

Impact: Scope is cut, quality is reduced, and the schedule is pushed back so that cheaper resources can be found. 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 mobile phone handset, your customer asks that the launch date is brought forward two weeks to coincide with a major industry show.

Impact: Costs increase as more people are added to meet the new deadline. Some features of the product 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 client asks that new features be added to the software after learning that a competitor's product will be in direct competition with their own. It is important the product includes these new features if it is to compete successfully.

Impact: The budget and schedule increase as a result of pushing up the final delivery date. More people are added 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, it is the project manager who 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 all changes that will impact cost, time, and scope.

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


Enjoyed this article? Now read 21 Ways to Excel at Project Management


Comments (2)

Topic: Understanding the Project Management Triple Constraint
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21st April 2018 7:17pm
Tor Christensen (PRINCE FREDERICK) says...
Excellent article. I want to know what diamond versus duds means as it applies to manage project change? Is this the same model used for managing project change, or is there a different diamond involved. I saw a video on lynda.com that spoke of this, and I am trying to get to the bottom of it.
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24th November 2015 9:39pm
Nyla Ahmed (Leeds) says...
Thank you for posting an article in Layman's terms. Very clear and concise and easy to digest. I enjoyed the read and even though I am a PM I've never heard of the project management diamond, but still use those as key indicators. Glad, I learned something new, I think this will stick.

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