Critical path
The critical path is the longest chain of dependent tasks through a project. It sets the earliest possible finish date, its tasks have zero total float, and any delay to one of them moves the project's finish by the same amount.
A project usually has several chains of work running side by side. The longest one decides when the project can finish; the shorter ones have float, time they can slip without moving the end.
The critical path changes as work happens. A task with float can slip by more than its float, and its chain then becomes the longest: the critical path has moved.
Worked example
| Task | Duration | Depends on | Scheduled | Total float |
|---|---|---|---|---|
| 1. Plan | 3 days | None | Days 1 to 3 | 0 days |
| 2. Build | 5 days | 1 | Days 4 to 8 | 0 days |
| 3. Write docs | 2 days | 1 | Days 4 to 5 | 3 days |
| 4. Release | 2 days | 2, 3 | Days 9 to 10 | 0 days |
Plan, Build and Release form the longest chain, so the project finishes on day 10; 3 tasks are critical. Write docs runs alongside Build with 3 days of float, so it is not on the critical path.
Open this example in the free delay simulator to change the durations, the links or the delay and watch the schedule move.