Estimation II — 3-point, COCOMO, function points

3-point (PERT) estimation

Instead of a single number, give three: Optimistic, Most-likely, Pessimistic. The weighted estimate is (O + 4M + P) / 6. The range (P − O) communicates uncertainty — a wide range means you're guessing; a narrow range means you have data.

COCOMO

COCOMO (Constructive Cost Model, Boehm 1981; COCOMO II 2000) is a parametric model for software effort. Inputs are roughly: source-lines-of-code (SLOC), project type (organic / semi-detached / embedded), and a set of effort multipliers (team experience, tools, complexity). Output: person-months.

↳ real-talk on COCOMO

You will be asked about COCOMO on the PMP. You will probably not use it day-to-day. Modern teams use story-point velocity for software. COCOMO matters as exam content and historical context, not as a daily tool.

Function points

Function point analysis (Albrecht, IBM 1979) sizes software by counting functions — inputs, outputs, queries, files, interfaces — weighted by complexity. Language-independent (a function point is the same regardless of whether you build it in COBOL or TypeScript), which is its main advantage over SLOC-based methods.

When to use each

Method	Use it for	Avoid for
3-point	Any deliverable where you need a defensible range	Where stakeholders only accept a single number

Estimation II — 3-point, COCOMO, function points.

3-point (PERT) estimation

COCOMO

Function points

When to use each

Sources cited