# A critical path method example you can work through

Calculate a critical path with a small original project network, see how float works, and understand why dependencies and resource limits still matter.

Source: https://tirtle.com/blog/critical-path-method-example
Publisher: Tirtle | Updated: 2026-10-10

## The short answer

The critical path is the longest duration path through a project's logical schedule network. In a simple unconstrained network, it determines the earliest possible finish. Calculate the connected paths, then check dependencies, calendars, resource limits, and changes before using the result as a delivery commitment.

## Build a small network

Consider an original project to prepare a training room. All durations are working days. Activities use finish-to-start relationships, with no lag. Configuration and content preparation can happen in parallel, and the example assumes the necessary people are available.

The work is listed below. Testing waits for both configuration and content preparation. That join is important: you cannot start testing just because the shorter branch is ready.

| Activity | Duration | Predecessor |
| --- | --- | --- |
| A: Confirm requirements | 2 days | None |
| B: Configure equipment | 4 days | A |
| C: Prepare training content | 3 days | A |
| D: Test the room | 2 days | B and C |
| E: Train the facilitator | 1 day | D |

## Calculate each complete path

The configuration path is A → B → D → E. Its duration is 2 + 4 + 2 + 1 = 9 days. The content path is A → C → D → E. Its duration is 2 + 3 + 2 + 1 = 8 days. The configuration path is critical in this network.

Use an elapsed-time convention starting at time zero. A finishes at time 2. B finishes at 6 and C at 5. D can start at 6, when both predecessors are complete, and finishes at 8. E finishes at 9. Stating the convention avoids confusing these values with inclusive calendar dates.

## Find the flexibility on the shorter branch

C could finish at time 6 without delaying D, so it has one day of total float in this simple network. It could start at 3 instead of 2 and still finish at 6. The critical activities have zero total float under the example's assumptions.

That does not make C unimportant or give everyone an extra day to spend. Float belongs to the schedule logic and may be shared across activities on a path. Constraints or resource changes can also alter it. Keep the schedule current rather than treating the first calculation as permanent.

## See how the critical path can change

Now change C from three days to five. The content path becomes 2 + 5 + 2 + 1 = 10 days. The configuration path remains nine. The content path is now critical, and the earliest finish becomes time 10 under the same assumptions.

If you shorten B by one day at this point, you do not shorten the project. D still waits for C. This is why a recovery action should target the actual controlling dependency. Even on a critical activity, adding people only helps when the work can realistically be shortened without unacceptable cost or risk.

## Check the model against real work

A logical network is useful, but it does not guarantee that a person can work on two parallel tasks at once. If B and C need the same specialist, account for that resource limit. Check nonworking days, review availability, external dates, and uncertainty in durations.

For practice, increase D by one day and calculate both paths again. The original network then takes ten days, with A → B → D → E still critical. Explain why changing a shared activity affects both paths before calculating a larger example.

## Your next step

Find the longest connected path, then validate the assumptions that let that schedule work. The critical path can change as the work changes.

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## Sources

- [PMI Lexicon of Project Management Terms (registration may be required)](https://www.pmi.org/standards/lexicon) | Project Management Institute

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