Project Network Diagram: Types & How to Draw One [2026]

A task list tells you what has to happen; it does not tell you what happens if one thing slips. A project network diagram does — it lays out every activity and the dependencies between them, so you can trace which delays ripple to the finish date and which ones the schedule can absorb. It is the backbone of any serious project schedule and a staple of the PMP and CAPM exams. This guide covers the project network diagram in full — what it is, the two ways to draw one, how to build it, and how it reveals the critical path.

What is a project network diagram?

A project network diagram is a visual map of a project's activities and the dependencies between them, drawn as a set of nodes connected by arrows that flow from the project's start to its finish. It shows the order work must follow — which activities depend on which — and, crucially, it exposes the critical path, the longest chain of dependent activities that determines the shortest possible project duration.

It is more than a picture. Because the diagram captures every dependency, it lets you calculate the earliest and latest each activity can start and finish, and therefore how much slack (float) each one has. The network is usually built from the work breakdown structure and feeds directly into the critical path method.

Activity-on-node vs. activity-on-arrow

There are two ways to draw a project network diagram, and the difference is what the boxes and arrows represent.

• Activity-on-node (AON), also called the precedence diagramming method, puts each activity in a node (box) and uses arrows only to show dependencies. This is the modern standard — it is what PMI teaches and what virtually all scheduling software uses, because it handles the different dependency types cleanly.
• Activity-on-arrow (AOA), the older style, puts each activity on an arrow and uses nodes to represent events (the start or end of activities). It is largely historical now and can require "dummy" activities to show certain relationships.

For the exam and for practice, assume activity-on-node unless a question explicitly says otherwise.

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How to create a project network diagram

Building a network diagram is a straightforward sequence that turns your task list into a connected schedule:

1. List the activities. Break the project down, usually from the work breakdown structure, into the individual tasks to be scheduled.
2. Sequence the dependencies. For each activity, identify which tasks must come before it. These predecessor relationships define the network's shape.
3. Draw the nodes and arrows. Place each activity in a box and connect the boxes with arrows in dependency order, flowing left to right from start to finish.
4. Add durations and run the passes. Enter each activity's duration, then work forward through the network to find early start and finish dates, and backward to find late start and finish dates.
5. Identify the critical path and float. The path with zero float is the critical path.

Each node carries a standard set of values once the passes are done — the early and late dates and the float — usually laid out like this:

How network diagrams reveal the critical path

Two passes through the diagram do it. The forward pass moves left to right and computes each activity's early start (ES) and early finish (EF) — the soonest it can happen. The backward pass moves right to left and computes the late start (LS) and late finish (LF) — the latest it can happen without delaying the project.

The gap between the two is the total float: how long an activity can slip before it pushes out the finish date. Total float equals LS − ES (or LF − EF). Activities with zero float sit on the critical path, so any delay to them delays the whole project; activities with float have slack the schedule can absorb. Our PMP formulas cheat sheet lists the float formulas alongside the other schedule calculations.

Project network diagram example

Here is the method on a small website launch, four activities in all. Design (4 days) must finish before anything else can begin. Once it is done, Build (6 days) and Content (3 days) run on parallel paths — and Test (2 days) can start only when both are complete. Running the forward and backward passes gives every activity its dates:

The diagram tells the whole story. There are two paths from start to finish: Design → Build → Test totals 4 + 6 + 2 = 12 days, while Design → Content → Test totals 9. The longer path is the critical path — drawn in red — and every activity on it has identical early and late dates: zero float, no room to slip. Content is the exception: it can finish as early as day 7 but is not needed until day 10, so it carries 3 days of float and can slip that far without moving the launch. And notice Test: it waits for Build, the later of its two feeds, because an activity cannot start until every path arriving at it is finished.

Network diagrams on the PMP® and CAPM® Exams

In the PMP exam, network-diagram questions are rarely "what is a network diagram" — they are applied. A question describes a schedule or gives a small network and asks you to reason about float, the critical path, or the effect of a delay. The common trap is treating an activity with float as if it were critical, or the reverse: forgetting that once a delay consumes an activity's float, that path becomes critical and has no slack left. Read every schedule question for how much float exists and where, before deciding what a delay actually costs.

Just as important is knowing that a delay to a non-critical activity does not move the finish date until it exceeds the float — so the correct response is often to monitor rather than to act. But watch for the flip side: when the float is used up, "keep reporting on schedule" is wrong, because the project has lost its buffer. The CAPM tests the same ideas more simply (reading a small network, identifying the critical path, and computing float) without layering in as much judgment. Our PMP Complete Study Guide works through the forward and backward pass step by step so the calculations become automatic.

PMP Practice Question: Network Diagrams and Float

During execution, an activity on a non-critical path that had 3 days of total float is reported 3 days late. A second, longer activity on that same path is scheduled to start next. The project sponsor notes that the project's completion date has not changed and asks the project manager to keep reporting the project as on schedule.

What should the project manager do next?

a) Continue reporting the project as on schedule, since the completion date has not moved.

b) Update the schedule to show that the path now has zero float, and flag the reduced flexibility and increased risk to the sponsor.

c) Crash the delayed path immediately to restore the original 3 days of float.

d) Reassign resources from the critical path to the delayed activity to prevent any further slippage.

Correct answer: B.

Rationale: The 3-day delay has consumed all 3 days of float, so that path now has zero float and is effectively critical — the completion date has not moved yet, but the buffer is gone, and any further slip on that path will now hit the finish date directly. The correct next step is to update the network to reflect the lost float and communicate the increased risk, not to report "on schedule" as though nothing changed, which is choice a). Choice c) crashes to restore a buffer the plan does not require, spending money and adding risk before any impact analysis. Choice d) protects the newly critical path by pulling resources off the already-critical one, trading one problem for a worse one. Reporting the real schedule status and the reduced flexibility is the professional response. For full-length, realistic, scenario-based practice built to train the PMI® mindset, take our PMP practice exams or, at the entry level, our CAPM practice exams.

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