Triple Constraint (Scope / Time / Cost)
The three interlocked dimensions that bound every project. Change one without compensation and another must give.
Explanation
Every project is constrained by:
- Scope — what’s being built (features, deliverables, quality)
- Time — when it must be done (schedule, milestones)
- Cost — how much it can cost (budget, resources)
The three are linked. There is no “faster, cheaper, better” without a trade-off:
| Change | Held fixed | Must give |
|---|---|---|
| Scope grows | Budget fixed | Timeline extends |
| Budget shrinks | Scope fixed | Timeline extends |
| Timeline shortens | Budget fixed | Scope decreases |
| Deadline fixed | — | Scope decreases AND budget increases |
Application
- At initiation, the charter fixes scope, time, and cost baselines. Stakeholders must acknowledge they can’t all be rigid.
- During execution, every change request should be evaluated against all three dimensions before approval. See change-management.
- In Agile, the triple constraint is the lens used to evaluate change decisions — scope is the most negotiable dimension since work is sliced into backlog items.
Evidence & Examples
From google-project-management-course: flexibility questions asked during scope definition (“What is the highest priority: hitting the deadline, sticking to the budget, or making sure the result meets quality targets?”) directly map to which corner of the triangle the customer refuses to compromise.