A constraint is a limiting factor that affects the execution of a project, program, portfolio or process.
In past versions, the PMBOK® Guide described the concept of the Triple Constraint. The Triple Constraint is made up of the scope, schedule and cost (budget) constraints that affect all projects.
Triple Constraint
Project Constraint Hexagon
On most projects all of these are important, but one is typically the most critical. By understanding what the most critical constraint driver is in a project, decisions can be made to support it.
For example, if your project was to build a stadium for the next Summer Olympics, your most critical constraint driver would be schedule. If you don’t meet the due date, nothing else matters!
When one of these constraints changes in a project, at least one other will also change. The Project Constraints and the critical driver must be considered throughout the project life cycle to analyze the impact of changes and support good decision making.
Project Constraint Changes
As represented below, to increase the scope of a project, e.g., add more seats to our Olympic stadium, or add functionality on a software development project, the cost will be higher, and likely the schedule will increase (lengthen) as well.
To shorten the schedule for a project, the cost will increase, or the scope must decrease, or the quality will be reduced, or the risk is increased, or some combination of those changes must take place.
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Materials are based on the Project Management Institute, A Guide to the Project Management Body of Knowledge, (PMBOK® Guide) 7th Edition, Project Management Institute, Inc., 2021
PMBOK is a registered mark of the Project Management Institute, Inc.