Planning & Scheduling 101

Planning & Scheduling 101 - the basics (fundamentals)

Critical Path Method: Getting Started in CPM & CPA (Critical Path Analysis)

This CPM guide gives you everything you need to start using the Critical Path Method—clear steps, worked examples, and practical schedules—so you can finish your next project faster and with less stress.

The Critical Path Method (CPM) is a straightforward but powerful way to analyse, plan, and schedule complex projects. It identifies the critical path—the longest chain of dependent tasks that determines the earliest possible finish date.

• CPM (also called Critical Path Analysis, CPA) maps task dependencies and pinpoints which activities are critical to on-time delivery.

CPM is one of project management’s foundational strategies. This beginner-friendly guide explains the core CPM formula and shows you how to apply it to your own projects.

• Early roots go back to large wartime projects (e.g., Manhattan Project), where structured planning techniques were developed to deliver results on time.

• The key insight: map the most important tasks and their order to estimate completion dates reliably.

Today, CPM remains a cornerstone of planning: when you can list key tasks and durations, you can estimate the timeline and budget with confidence.

If this sounds like jargon—don’t worry. This guide breaks CPM down step by step.

Understand the Critical Path Method

Have you heard of the Theory of Constraints (TOC)?

• Introduced by Eliyahu Goldratt (The Goal, 1984).

• Progress is limited by a small number of constraints.

CPM is similar in spirit but focuses on time and task sequence:

• A project’s success depends on completing certain tasks, in order, along the critical path.

• Delay a critical task → delay the whole project.

What is the Critical Path Method, and what is a Critical Task?

Every project has core tasks that must happen for completion. A critical task is one where any delay delays the entire project.

Example: Making a pizza

• Critical steps:

  • Make the pizza base

  • Heat the oven

  • Prepare the pizza toppings

  • Bake the pizza

• Non-critical add-ons (nice, but optional): seasonings, veggies/cheese, etc.

• The sequence of the three core steps is the critical path for this “project”.

That’s CPM in a nutshell: identify the minimum sequence of must-do tasks and their order.

Critical Path Method Definition

PMBOK® definition: "The Critical Path Method is the sequence of scheduled activities that determines the project's duration.”

Key points:

• Activities on the critical path must be done and in order.

• In any project there are multiple sequences; the critical path is the longest (by duration).

• The total duration of that path gives the minimum project length.

House-build example (simplified):

• Some sequences take longer (e.g., foundation → walls → roof) than others (e.g., fixtures).

• The longest valid sequence determines the overall schedule.

The Critical Path Algorithm Explained

CPM is an algorithmic way to decide what matters most and when.

Basic mechanics:

• Build a network (flowchart) of activities with durations.

• For each activity, compute:

  • ES (Earliest Start) = max (EF of all predecessors)

  • EF (Earliest Finish) = ES + duration

• The path with the largest EF at the end node is the critical path.

• That final EF is the minimum project duration.

Practical steps:

• List tasks with durations and predecessors.

• Draw a network diagram with arrows for dependencies.

• Forward-pass to calculate ES/EF across the network.

• The longest resulting path is critical.

Float or Slack in Project Management

Float (slack) is how long you can delay a task without causing a delay.

• Free float: delay permitted without delaying the next dependent task.

• Total float: delay permitted without delaying the overall project.

• Tasks on the critical path have zero float.

Why float matters:

• Guides resource allocation:

  • High-float tasks can spare resources temporarily.

  • Zero-float (critical) tasks demand priority attention.

Quick example (pizza):

• “Heat the oven” = zero float (critical).

• “make the pizza base” = float (can be done before baking the pizza).

DEALING WITH CONTINGENCIES AND CONSTRAINTS

Projects rarely go exactly to plan. CPM supports two classic schedule compression techniques:

1. Fast Tracking

• Run eligible activities in parallel to shorten the duration.

• Only for tasks without hard finish-to-start constraints.

• Trade-offs:

  • Requires more coordination/resources.

  • Potential quality risk if spread too thin.

2. Crashing

• Add resources to reduce the duration of certain activities.

• Works best when:

  • More resources meaningfully speed the task (linear-ish gains).

  • You can pull from high-float tasks without jeopardizing the schedule.

• Use sparingly; focus on tasks that truly benefit from added capacity.

WHAT ARE THE BENEFITS OF THE CRITICAL PATH METHOD?

• Reduce delays: focus on the tasks that drive the end date.

• Visualize dependencies: clarify sequencing and handoffs for all stakeholders.

• Improve organization: break complex work into manageable, ordered activities.

• Optimize efficiency: allocate people and budget according to task criticality.

• Use float smartly: shift resources from high-float to zero-float activities as needed.

• Exam relevance: CPM is fundamental for PMP® preparation.

HOW TO USE THE CRITICAL PATH METHOD

PMs use CPM to schedule tasks for the fastest, most economical delivery while anticipating dependencies, bottlenecks, constraints, and risks.

• If you understand Work Breakdown Structure (WBS), CPM becomes intuitive.

• Below is a practical process you can follow.

A STEP-BY-STEP PROCESS FOR USING CRITICAL PATH METHOD

Prerequisite: a solid WBS (deliverables broken into components).

Step #1: Identify activities based on WBS

• WBS lists deliverables (nouns); CPM needs activities (verbs).

• Create a thorough activity list required to produce each deliverable.

Step #2: Identify all dependencies

• Classify tasks as:

  • Dependent (must follow others).

  • Concurrent (can run in parallel).

• Create activity sequences by ordering dependent tasks.

Step #3: Create a network diagram

• Draw nodes for activities; connect with arrows for dependencies.

• This becomes your critical path analysis chart.

Step #4: Estimate the duration of each activity

• Use:

  • Experience, historical data, benchmarks, or extrapolation.

• Consider three-point estimates:

  • A (best), B (most likely), C (worst)

  • Simple average: (A + B + C) / 3

  • Weighted (more weight on B): (A + 2B + C) / 4

• Add durations to your network diagram.

Step #5: Calculate the Critical Path

• Forward-pass:

  • First activity starts at 0; EF = ES + duration.

  • For each successor: ES = max(EF of predecessors).

• The sequence with the largest ending EF is the critical path.

Step #6 (Optional): Determine Floats

• Compare the critical path to the second-longest sequence:

  • Float ≈ (Critical path duration − Second-longest duration).

  • Activities shared with the critical path have zero float.

• Use floats to guide resource levelling.

CRITICAL PATH METHOD VS. GANTT CHART

• CPM:

  • Best for complex dependencies, accurate duration prediction, and identifying the drivers of the end date.

• Gantt chart:

  • Best for tracking progress and communicating timelines; adapts well to frequent changes.

• Often used together: CPM to analyse criticality; Gantt to visualize and track.

WHY MUST NON-CRITICAL TASKS BE MONITORED?

• They still must be completed before the project finishes.

• If forgotten or allowed to slip excessively, they can become critical and push the end date.

• Regular monitoring keeps them within available float.

CRITICAL PATH METHOD VS. PERT

• PERT (probabilistic):

  • Assumes task durations are uncertain; uses distributions to estimate project length.

• CPM (deterministic):

  • Assumes tasks are well-defined; computes the longest path to determine finish dates.

• Choose based on context:

  • High uncertainty → PERT.

  • Stable, well-defined scope → CPM.

RECENT UPDATES AND DEVELOPMENTS IN CPM

• Elasticity/flexibility concepts: schedule with built-in tolerance for inevitable delays.

• Predictive analytics & AI: analyse patterns to optimize sequences and identify emerging critical paths.

• EVM (Earned Value Management): combine cost, schedule, and scope metrics; often paired with CPM to assess performance against plan.

Most new approaches still build on CPM’s core ideas.

USE CRITICAL PATH FOR BETTER PROJECT MANAGEMENT

CPM remains one of the most practical ways to deliver projects:

• Compress schedules thoughtfully (fast track, crash where it pays off).

• Resolve resource gaps by reallocating from high-float tasks.

• Capture lessons learned to improve future estimates and plans.

Key takeaway:

• Don’t rely only on a quick CPM software package—understand how CPM works so you can apply it correctly and adapt as things change.

• Keep your schedule current (up to date) throughout the project.

• Using project management software with CPM and Gantt capabilities (e.g., enterprise PM tools) makes it easier to model dependencies, visualize critical paths, and update plans rapidly.

Want to learn more? Download your 100-page free e-book 'Planning & Scheduling Fundamentals'