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What are the three primary variables (or triple constraints) of project management?

If you’ve ever taken a project management course, you’ve probably got a knee-jerk response to this question:

  • Scope
  • Time
  • Cost

For 50+ years, the triple constraint theory has been the standard for project managers, but like any model, it may be a bit more complex when applied to real life situations.

What Are The 3 Triple Constraints of Project Management?

Also known as the “iron triangle” or the “project management triangle”, the triple constraints of project management refer to the relationships between a project’s scope, time, and cost.

The "iron triangle" of project management—scope, time, and cost—depends on quality.

Let’s dive into each side of the project triangle to explain this further.


Project scope refers to the extent, range, breadth, reach, confines, dimension, realm, gamut, spectrum, or spread of the work that’s to be done on a project.

It encompasses the sum of products and services to be provided, describing what’s being done and how much of it. You can learn more about scope statements and scopes of work (and a guide to writing them) in our statement of work guide (which includes a handy template).

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Simply put, the duration or amount of time (usually expressed in number of hours) required to complete the project or tasks within the project.


Project cost refers to the resources—financial and otherwise—required for project execution. Costs might include labor, hardware, software, and other charges.

Check out this short & sweet overview here:

How Does The Triple Constraint Affect Projects?

The triple constraint doesn’t exist simply as a cutesy mnemonic device. The whole premise of the triple constraints of project management is that the three factors of scope, project time, and cost are inextricably linked.

Simply put, if you make changes to one side of the triple constraint triangle, it will also affect the other sides of the triangle. Takes you straight back to geometry class.

The most common triple constraint model places “quality” in the center of the triangle to illustrate that the quality of a project depends on the project’s scope, budget, and time spent. If you want to maintain a consistent level of quality (or, in geometry class, a consistent area within the triangle), making changes to one side of the triangle requires the other sides to adjust.

Math aside, this idea is intuitive. If you’re going to ask for something to be delivered faster (time), you have to pay more (cost). If you’re trying to save some money (cost), sometimes you can achieve this by delivering a simpler product (scope).

The triple constraint is especially helpful in conversations with clients, both when initially determining the scope of a project and when handling change requests along the way. Digital agencies live in a competitive environment, and it’s common to feel pressure to deliver something comprehensive as cheaply (and quickly!) as possible.

While that is possible in some scenarios, the project management triangle reminds us that, most of the time, projects cannot be simultaneously cheap, comprehensive, and fast. We have to know our priorities to decide “what’s gotta give”.

The iron triangle teaches us that the Venn diagram for dream projects (comprehensive, fast, and cheap) is often just that—a dream.

A Triple Constraint Example

So, how does this work in practice? Let’s take a website development project:

  • Scope: ecommerce website
  • Time: 6 months
  • Cost: $500,000.

Say the client originally thought that they’d be able to supply content from their team, including SEO-friendly product descriptions. They’ve recently learned that their team doesn’t have bandwidth to produce the content, and so they’re asking your project team to do it. 

Although you might like to say yes to this request, the iron triangle reminds project managers that you can’t increase project scope without factoring in its relationship with time and cost. Naturally, the client would prefer to change the scope without the time or cost of the project changing (this is a whole issue in and of itself—see my post on managing scope creep). 

A savvy project manager understands the dynamic between scope, time, and cost—and you know that trade-offs are inevitable. To deliver a successful project, the project manager must help key project stakeholders understand this dynamic, too.

So, how do you navigate that conversation? The key is not to say no to the request outright. Your mantra is “we can do it, but…”

  • the project schedule will need to shift back a week OR
  • another piece of the scope or functionality must come out OR
  • the client needs to fund an extra week of work.

You know best which lever to pull to get your client to agree. If they still aren’t getting it, whip out the diagram from this article and explain that quality suffers if the constraints change (as do the chances of project success). That tends to spook ‘em. 

Author's Tip

Remember: There are no circumstances in which you can agree to modify one constraint without impacting the other two.

Why The Triple Constraints May Not Be A Triangle Anymore

Despite its longevity, opinions vary as to the accuracy and usefulness of the project management triangle. Some theories have stuck with the triangle concept but changed the types of constraints on each side. Regardless of the varying perspectives, every PM knows that managing a project is more complex than the iron triangle variables suggest.

The Project Management Institute (PMI) agrees. In its latest version of the Project Management Body of Knowledge (PMBOK), PMI recognizes that project managers usually deal with more than three constraints that may shift throughout the project life cycle. Sample constraints might include quality standards, sustainability guidelines, or regulatory compliance requirements.

Despite the added complexity, the triple constraint model is still a great way to conceptualize the relationships between the high-level dynamics involved in project management.

3 Tips For Managing The Triple Constraint IRL

Although admittedly simplistic, the triple constraints of project management are often a useful way to represent expectations in a project. Here’s how to use it in real life to establish parameters that make the most sense based on your clients’ chosen priorities.

Is Cost The Biggest Priority?

If you absolutely have to stay within a fixed project budget, then the client may need to be more flexible on timeline and scope. With delivering on budget as the biggest priority, it’s likely that only the most business-critical change requests will be approved.

So, when changes come up, you’ll probably look to these measures:

  • adjust the project schedule
  • scale back the scope of the project
  • agree upon reduced quality of select project deliverables

To help you communicate the costs and cost estimates of the project to your clients, use resource management software, where you can draw up reports on the project team’s capacity, resource utilization, and performance for projects, clients, and individuals.

You could also use a Gantt chart to create a detailed work breakdown structure (WBS).

Is Time The Biggest Priority?

In cases where the deadline matters most, then more flexibility will be required with respect to the cost and/or scope.

Expediting the project to satisfy the time constraint might mean:

  • putting more resources on the line, increasing cost
  • cutting back the scope and/or quality of the end product

When precise time estimates and deadlines are a priority, you should take a moment to set yourself up with the right time tracking tools: use past project reports to make accurate time estimates and track team member hours to make sure you’re staying on schedule and hitting milestones as the project progresses.

Is Scope The Biggest Priority?

If scope matters most, the client may need flexibility to add features throughout the project as they discover more about their customers. If what matters most is being able to accommodate the features that are in scope, then the client has to remain open to:

  • flexible timing as the team accommodates scope changes
  • increased cost for adding deliverables to the scope that were not included during project planning at the outset of the project

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Looking For More?

Project constraints will always exist. It’s up to you as the project manager to communicate this give-and-take relationship with your clients so they understand that, if one constraint changes, the other constraints are likely to be affected, potentially putting the project goals in jeopardy.

For more information on managing project constraints, check out my blog and newsletter, or scan DPM’s list of the best project management software, most of which include a bundle of features for time management, scheduling resources, and creating process documentation.

By Sarah M. Hoban

Sarah is a project manager and strategy consultant with 15 years of experience leading cross-functional teams to execute complex multi-million dollar projects. She excels at diagnosing, prioritizing, and solving organizational challenges and cultivating strong relationships to improve how teams do business. Sarah is passionate about productivity, leadership, building community, and her home state of New Jersey.

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  • Thank you, Sarah, for your insightful article. I particularly appreciated the extra constrains you were mentioning on top of the usual three. In the world of IT systems integration projects, the quality standards, missed requirements and compliance requirements' impact are often derailing the projects


  • Such a good article! Will be visiting this website more often


  • The triple constraints of project management - cost, time, and scope - are essential for ensuring a successful outcome. Balancing these constraints effectively can be a challenging task, but it is crucial for delivering a project on time, within budget, and to the satisfaction of all stakeholders.


  • I really like this example. It shows that PM can manage the project and make a right decision.


  • Nice read! Great article 👍 Thank you so much 😊


  • Hi, this link is not working "best project management tools"


  • I think this model is great and definitely worth keeping as the quality, benefit and risk are quite similar to a project's scope. Thanks for sharing, Ben. This article was quite insightful.


  • You can only change the pyramidal triangle if you have speed and skill


  • nice read


  • Great article!! Thanks so much. This really lays out a comprehensive overview of considerations when building and responding to request for adjusting scope. The other linked articles are also extremely helpful - great layout for diverse learners (ie: including all the software logos/images, then detailed breakdowns). Thank you!


  • I believe the below constraints are still very valid. PM's sometimes get a good idea where the trade offs can be done (what is flexible, cost or time) during the charter phase and can steer the team accordingly based on what is truly important in terms of business outcomes.