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Find the critical path, one step at a time
Which activities control the finish date? Use this five-activity CAPM example to find the critical path, calculate float and check what a delay really changes.
The longest connected path controls the earliest finish. A delay on a shorter path may use up spare time before it delays the project.
1. Start with the work and what must happen first
A team is setting up a training room. Preparing the room and configuring the equipment can happen at the same time. Installation must wait for both.
| Activity | Duration | Must wait for |
|---|---|---|
| A · Confirm requirements | 2 days | Nothing |
| B · Prepare the room | 4 days | A |
| C · Configure equipment | 3 days | A |
| D · Install equipment | 2 days | B and C |
| E · Test and hand over | 1 day | D |
For this example, every link is finish-to-start: the earlier activity finishes before the next begins. Assume one working calendar, no waiting gaps and enough people for B and C to run together.
2. Compare complete paths, not individual tasks
Follow each connected route from the start to the finish and add its durations.
Through room preparation
9 working days
2 + 4 + 2 + 1 = 9
Through equipment configuration
8 working days
2 + 3 + 2 + 1 = 8
The critical path is A → B → D → E. It takes nine working days and controls the earliest finish in this schedule. The equipment can be configured sooner, but installation still has to wait for the room.
3. Find how much delay the shorter path can absorb
Total float is how long an activity can move without delaying the project finish or violating a schedule constraint. Here, C can take one extra day before it holds up D: the two paths differ by one day.
If C takes one extra day
Both paths take nine days. The project can still finish in nine days, but C has no float left. Both paths are now critical.
If B takes one extra day
The longer path becomes ten days. With no other change, the project finishes one day later. B had no float to absorb the delay.
This path-length shortcut works for this simple network. Larger networks need a forward and backward pass to calculate each activity's early and late dates. Do not assume every noncritical activity has the same float.
4. Try a change before reading the answer
Equipment configuration, activity C, now needs five days instead of three. Everything else stays the same. What is the new critical path, and how long does the project take?
Check the answer and reasoning
A → C → D → E is now the critical path: 2 + 5 + 2 + 1 = 10 days. The other path still takes nine days.
C increased by two days, but the project finish moved by only one day. Its first extra day used the float; the second delayed installation. Recalculate after a change instead of assuming the original critical path still controls.
Sources and scope
The training-room example and calculations were created by LevelUP. These PMI references explain the underlying scheduling method and terminology.
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Try the flashcardsThese are original LevelUP practice examples, not PMI exam questions. LevelUP is an independent education provider and is not affiliated with or endorsed by PMI.