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🧭 Methodologies & Frameworks📅 Scheduling & Time Management

Critical Path Method

The critical path method (CPM) finds the longest chain of dependent activities through a project — the sequence that determines the shortest possible finish date, and the tasks where any delay delays the whole project.

The critical path method is a scheduling technique that models a project as a network of activities with durations and dependencies, then calculates the earliest and latest each activity can start and finish. The critical path is the longest path through that network; its length is the project’s minimum duration. Activities on the critical path have zero float — no slack — so a one-day slip on any of them slips the whole project. Activities off the critical path have float and can move within limits without affecting the end date.

Critical Path Method at a glance

Category
Methodologies & Frameworks · Scheduling & Time Management
Type
Methodology / framework
Also known as
CPM
Appears in
2 sections
Related
Critical Chain Project Management, Program Evaluation and Review Technique, Adaptive Project Management

Also known as: CPM.

Why it matters

CPM tells you two things every project manager needs: how long the project will take, and which tasks you cannot afford to let slip. That lets you focus management attention where it matters, make informed decisions about compressing the schedule (crashing or fast-tracking), and understand the knock-on effect of any delay. Without it, every task looks equally urgent — which means none of them get the right attention.

When to use it

Use CPM on any schedule-driven project with meaningful task dependencies — construction, engineering, product launches, event planning. It is most valuable when the deadline is fixed and you need to know exactly where the risk to that deadline lives. For very small or highly uncertain work, a simpler board or rolling-wave plan may serve better.

How to use it

  1. List all activities and estimate each one’s duration.
  2. Determine dependencies — which activities must precede which.
  3. Draw the network diagram and run a forward pass to get each activity’s Early Start (ES) and Early Finish (EF).
  4. Run a backward pass to get Late Start (LS) and Late Finish (LF).
  5. Calculate float (LS − ES). Activities with zero float form the critical path.

Example

A project has paths A→B→D→F (3+4+5+3 = 15 days) and A→C→E→F (3+2+2+3 = 10 days). The longer path, 15 days, is the critical path; B and D are critical. C and E share float, so a short delay there is absorbed — but any delay to A, B, D or F pushes the finish date.

Template

A CPM worksheet lists each activity with duration, predecessors, ES/EF/LS/LF and float, and flags the critical path. Try it live in the calculator below.

Browse templates →

Tools

Primavera P6Microsoft ProjectExcel (with formulas)SmartsheetGanttPRO

Formula & calculator

Float = LS − ES = LF − EF · Critical path = path with zero float

Try it yourself: Critical Path Calculator computes this from your own figures.

Open the Critical Path Calculator →

FAQs

What is the difference between the critical path and the critical chain?
The critical path is the longest sequence of dependent tasks. The critical chain (from CCPM) also accounts for resource constraints and manages buffers rather than task-level padding.
Can a project have more than one critical path?
Yes. If two paths have equal, maximum length, both are critical — and the project becomes more fragile because there are more tasks with zero float.
What is float or slack?
The amount of time an activity can be delayed without delaying the project (total float) or its successors (free float). Critical activities have zero total float.

Alternatives

  • PERT — adds three-point probabilistic durations to the same network
  • Critical Chain Method (CCPM) — resource-aware scheduling with buffers
  • Kanban / flow — for continuous work where a fixed critical path is less meaningful