Calculate a critical path
Use forward and backward passes to find how much each activity can move. In a finish-to-start network, a successor begins only after each of its immediate predecessors is finished.
A project with a parallel branch
A: Set the brief, 3 days. B: Build the prototype, 5 days after A. C: Prepare the test plan, 2 days after A. D: Run testing, 4 days after B and C. E: Release milestone, 0 days after D.
Forward pass
Begin A at 0 and finish it at 3. B and C start at 3. B finishes at 8 and C finishes at 5. Testing waits for both, so D starts at 8 and ends at 12. E marks the earliest finish at 12.
Backward pass and float
Start at the project finish of 12. D must start by 8, so C must finish by 8 and start by 6. Its early start was 3. C has 6 − 3 = 3 days of total float. A, B, D, and E have zero total float. They form the critical path.
Check what the model assumes
Use consistent time units. This calculator assumes finish-to-start dependencies with no lead or lag. Calendar closures, resource limits, and deadlines can change a real project schedule.
Try this example in the diagram builder →
See the Project Management Institute’s explanation of critical path calculations.