Critical Path Example (CPM): Find the Real Finish Date, Float, and What Can’t Slip
If your plan “looks fine” but deadlines keep slipping, the problem is usually the same: the team isn’t clear which tasks actually control the finish date. This critical path example shows how to calculate it quickly—so you can protect the work that cannot move.
What “critical path” actually means (in plain language)
The critical path is the longest chain of dependent tasks from start to finish. Any delay on that chain delays the entire project. Tasks not on the critical path have float (also called slack)—they can move a little without changing the final finish date.
A simple critical path example (CPM) you can do in minutes
Let’s use a small project with dependencies. Your goal is to find the earliest finish date and identify which tasks have zero float.
| Task | Duration (days) | Depends on |
|---|---|---|
| A — Define scope | 2 | — |
| B — Requirements | 4 | A |
| C — Design | 3 | B |
| D — Build | 6 | C |
| E — Test | 3 | D |
| F — Training | 2 | C |
| G — Launch | 1 | E, F |
Step 1: Forward pass (Earliest Start / Earliest Finish)
- A finishes at day 2.
- B starts at day 2 → finishes at day 6.
- C starts at day 6 → finishes at day 9.
- D starts at day 9 → finishes at day 15.
- E starts at day 15 → finishes at day 18.
- F starts at day 9 → finishes at day 11.
- G depends on E and F, so it starts at the latest of their finishes: max(18, 11)=18 → finishes at day 19.
Step 2: Backward pass (Latest Start / Latest Finish) + Float
Now work backward from the finish date (day 19) to find how late each task can start without moving the finish date. The key takeaway most teams care about is float:
In this example, the chain A → B → C → D → E → G controls the finish. Task F has float because it finishes earlier than task E, and G can’t start until E is done anyway.
How to use CPM with your Gantt (without turning it into a math project)
- List tasks with clear start/finish definitions.
- Add dependencies (what truly must happen before what).
- Estimate durations in days (don’t over-precision this).
- Identify the critical chain and mark it visually.
- Manage weekly by protecting critical tasks and removing blockers early.
