Three-Point Estimating (PERT) Formula

Hello! I’m Joe, your instructor, and in this lesson, we’re going to explore another incredibly useful project management tool: the Three-Point Estimating, or PERT, Formula.

This technique is incredibly useful for calculating a weighted average duration or cost estimate. It does this by considering three scenarios: an optimistic estimate, a pessimistic estimate, and the most likely outcome. The benefit? This technique helps in providing more realistic estimates by actively accounting for uncertainty.

So, what does this powerful formula look like?

Formula: E = (O + 4M + P) / 6

Let’s break down what each symbol means:

• E stands for the Expected Value, which can be either the Duration or the Cost.
• O is your Optimistic estimate, representing the best-case scenario.
• M is your Most Likely estimate, which is the realistic scenario.
• P is your Pessimistic estimate, covering the worst-case scenario.

Let’s put it into practice with an example:

Imagine a task has an optimistic estimate (O) of 8 days, a most likely estimate (M) of 12 days, and a pessimistic estimate (P) of 22 days.

Using our formula:

E = (8 + 4 × 12 + 22) / 6

E = (8 + 48 + 22) / 6

E = 78 / 6

E = 13 days

The interpretation here is that the expected duration for this specific task is 13 days.

Mastering these formulas and their application is key to your success, especially when you’re tackling practice questions that involve calculations for exams like the PMP. Keep this formula sheet handy for quick reference!