Schedule · tool 2 of 7

Critical Path Method (CPM)

Critical Path Method (CPM): finds the chain of tasks that sets the project’s end date — the tasks you can’t let slip.

Best for: Deadline-driven projects · Time: 1–2 hours
Domain: Schedule · Focus area: Planning

A → B → D = 10 days is the critical path (blue). C can slip 3 days without moving the end date.

How it works

Tasks and their dependencies form a network. The critical path is the longest chain through it: its tasks have zero “float” (slack), so any delay on them delays the whole project.

Forward pass: earliest start and finish of each task.
Backward pass: latest start and finish without moving the end date.
Float = latest start − earliest start. Zero float = critical.

How to apply it

List activities with durations and predecessors (your Gantt already has them).
Let your tool compute — or calculate — earliest and latest dates.
Highlight zero-float tasks and give them your best people and closest follow-up.
To finish earlier, shorten critical tasks only: add resources (crashing) or overlap tasks (fast-tracking).

In practice

Adding a developer to a non-critical task costs money and gains nothing. Adding one to a critical task can move the end date.

Pro tip

The critical path changes as work progresses. Re-check it every time you update the schedule.

Use it

Playbook: We are going to miss the date

Quick check

Task C has 3 days of float and slips 2 days. What happens to the end date?

Sources

PMBOK® Guide, 8th edition, and The Standard for Project Management (PMI, 2025)

Last reviewed 2026-11-02 against the PMBOK® Guide, 8th edition · Practitioner review pending · How this guide is made