Critical Path Method Example: Step-by-Step With Numbers

The critical path method is arithmetic, not software. This is one complete pass on a ten-activity office relocation, with every number shown, so you can reproduce it on any project by hand.

Step 1 — activity list and dependencies

Step 2 — forward pass (early dates)

Early Start = the latest Early Finish among predecessors. Early Finish = Early Start + duration. Day 0 is the morning of day one, so an activity finishing at 4 has consumed days one to four.

Project duration is 44 working days. That is the earliest possible completion given this logic — not a target, a consequence.

Step 3 — backward pass (late dates)

Set the final activity's Late Finish equal to its Early Finish (44), then walk backwards. Late Finish = the earliest Late Start among successors. Late Start = Late Finish − duration.

Step 4 — float and the critical path

The critical path is A → B → C → E → H → I → J, totalling 4 + 6 + 8 + 15 + 6 + 3 + 2 = 44 days. The D → F → G chain carries three to four days of float, which is why paying a premium to accelerate IT procurement would buy exactly nothing.

Step 5 — compress the schedule

Compress by five or more days and the D → F → G chain becomes critical too. Recalculate after every change; a compressed schedule usually has more critical activities and therefore less tolerance than the plan it replaced.

Doing this on your own project

1. 1List activities at work-package level — ten to forty rows is the useful range for a hand calculation.
2. 2Record only genuine predecessors; convenience dependencies invent a false critical path.
3. 3Run the forward pass for early dates, then the backward pass for late dates.
4. 4Compute total float and mark every zero-float activity as critical.
5. 5Re-run after every actuals update — the critical path migrates during delivery.