Slack time measures how long an activity can be delayed without delaying later activities or the project completion date. Calculate it from earliest and latest schedule times. section 13.3.3
Use the schedule comparison to classify activities:
- Compute slack as latest start minus earliest start, or latest finish minus earliest finish; both calculations produce the same result. section 13.3.3
- Classify activities with zero slack as critical path activities because any delay directly affects the project timeline. section 13.3.2
- Treat activities with positive slack as noncritical, allowing delay up to the available amount without affecting completion. section 13.3.3
- Obtain earliest times through a forward pass and latest times through a backward pass across the project network. section 13.3.3
Automated reporting tool schedule
The computed schedule assigns activities F and H five weeks of slack and activity I nine weeks. Activities A–E, G, and J–L have zero slack and therefore form the critical path.
For larger networks, represent activities, dependencies, and expected durations in a pandas DataFrame, then automate forward-pass, backward-pass, and slack calculations with Python and NumPy. section 13.3.4
