Three-Point Estimating: Formula, Examples and When to Use It

Quick answer

Three-point estimating: Optimistic, Most likely, Pessimistic → expected = (O+4M+P)/6 (PERT) or (O+M+P)/3 (triangular) — the honest estimate that carries its uncertainty.

The three numbers

O (best case), M (most likely), P (worst case) — the range captures the uncertainty a single number hides.

The formulas

Triangular: (O+M+P)/3; PERT beta: (O+4M+P)/6 — PERT weights the likely; use PERT for skewed guesses.

The variance

(P-O)/6 = standard deviation — the spread tells you how uncertain the estimate is.

Using them

Three points on uncertain tasks → expected values + confidence ranges on the schedule.

Bottom line

Three-point estimating: Optimistic, Most likely, Pessimistic → expected = (O+4M+P)/6 (PERT) or (O+M+P)/3 (triangular) — the honest estimate that carries its uncertainty.

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