Project management triangle

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The project management triangle (called also the triple constraint, iron triangle and project triangle) is a model of the constraints of project management. While its origins are unclear, it has been used since at least the 1950s.^[1] It contends that:

1. The quality of work is constrained by the project's budget, deadlines and scope (features).
2. The project manager can trade between constraints.
3. Changes in one constraint necessitate changes in others to compensate or quality will suffer.

For example, a project can be completed faster by increasing budget or cutting scope. Similarly, increasing scope may require equivalent increases in budget and schedule. Cutting budget without adjusting schedule or scope will lead to lower quality.

"Good, fast, cheap. Choose two." as stated in the Common Law of Business Balance (often expressed as "You get what you pay for.") which is attributed to John Ruskin but without any evidence and similar statements are often used to encapsulate the triangle's constraints concisely.^[2][3] Martin Barnes (1968) proposed a project cost model based on cost, time and resources (CTR) in his PhD thesis and in 1969, he designed a course entitled "Time and Cost in Contract Control" in which he drew a triangle with each apex representing cost, time and quality (CTQ).^[4] Later, he expanded quality with performance, becoming CTP. It is understood that the area of the triangle represents the scope of a project which is fixed and known for a fixed cost and time. In fact the scope can be a function of cost, time and performance, requiring a trade off among the factors.

In practice, however, trading between constraints is not always possible. For example, throwing money (and people) at a fully staffed project can slow it down.^[5] Moreover, in poorly run projects it is often impossible to improve budget, schedule or scope without adversely affecting quality.