Project Management guide · Planning and scope
Project Constraints: The Triple Constraint and Beyond
Constraints are limits that a project must work within. Understanding them, and how they interact, is essential to making good trade-offs.
Key takeaways
- Scope, time and cost form the triple constraint, with quality at the centre.
- Other constraints include resources, risk and regulation.
- Agree which constraint is most fixed and manage trade-offs openly.
The triple constraint
Scope, time and cost are linked: change one and at least one other usually changes. Quality sits at the centre and suffers if the three are squeezed together.
Six common constraints
| Constraint | Example |
|---|---|
| Scope | Must include a payment feature |
| Time | Must launch before the trade show |
| Cost | Budget capped at $200,000 |
| Quality | Must meet accessibility standards |
| Resources | Only two developers available |
| Risk | Low risk tolerance for regulatory issues |
Other constraints include regulation, technology, contracts and stakeholder expectations.
Managing trade-offs
- Agree with the sponsor which constraint is most fixed.
- Show options and their impact when something changes.
- Use techniques such as fast-tracking and crashing for time constraints.
- In Agile, fix time and cost and let scope flex.
Constraints vs assumptions
Constraints are known limits; assumptions are things believed true but not proven. Both should be documented and reviewed.
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Frequently asked questions
What are project constraints?
Limits within which a project must operate, such as time, cost and scope.
What is the triple constraint?
The relationship between scope, time and cost.
Is the project management triangle the same as the triple constraint?
Yes. It is another name for the triple constraint.
Which project constraint is most important?
It depends on the project; agree it with the sponsor.
How do project constraints affect quality?
Squeezing scope, time and cost together typically lowers quality.
Which project constraint covers resources?
The resource constraint: limited availability of people, equipment or materials.
Where are project constraints documented?
In the charter, scope statement and project plan.
What is the difference between a project constraint and a risk?
A constraint is a known limit; a risk is an uncertain event.
How does Agile handle the triple constraint?
It typically fixes time and cost per iteration and lets scope vary.
Can project constraints change?
Yes, but changes should be approved and their impact assessed.