Critical Path Calculator

The critical path is the longest sequence of dependent tasks in a project. Its length is the minimum time the project can take, and any delay on it delays the finish date. This calculator identifies that path from your activity list and shows how much slack the other activities have, so you know where to focus attention.

How to use it

1. List the activities with their durations.
2. Enter each activity's predecessors, the tasks that must finish before it can start.
3. Calculate to see the project duration, the critical path and the float of each activity.

Worked example: a small office fit-out

• A: Strip out, 4 days
• B: Electrical first fix, 6 days, after A
• C: Plumbing first fix, 3 days, after A
• D: Drywall, 5 days, after B and C
• E: Order furniture, 10 days, no predecessor
• F: Decorate and install furniture, 4 days, after D and E

Path A, B, D, F takes 4 + 6 + 5 + 4 = 19 days. Path A, C, D, F takes 16 days and E, F takes 14 days. The critical path is A, B, D, F. Plumbing has 3 days of float and furniture ordering has 5 days.

Managing the critical path

• Monitor critical activities daily; they have no margin.
• Watch near-critical paths with small float, because a short delay can make them critical.
• Shorten the project by adding resources to critical tasks, overlapping them, or changing logic, not by speeding up non-critical work.
• Recalculate after every progress update, because the critical path can move.