HKSM
Late Start Date (LS)
In critical path method scheduling, the latest time an activity can begin its remaining work without delaying the project, as dictated by the network logic, the required project finish date, and any schedule constraints.
Key Points
- Calculated during the backward pass of the critical path method.
- Driven by successor relationships, the target project completion date, and schedule constraints; tighter limits reduce the LS.
- Computed as LS = LF - duration, accounting for any leads or lags.
- On the critical path (zero total float), LS equals ES.
Example
Assume the project must finish by day 60. Activity X has a duration of 6 days, and the backward pass yields a latest finish (LF) of day 40. The late start (LS) is 40 - 6 = day 34. Starting Activity X after day 34 would push its finish beyond day 40 and risk delaying the overall project.
PMP Example Question
An activity has a duration of 4 days and a latest finish (LF) of day 18. What is its late start (LS)?
- Day 14
- Day 18
- Day 22
- Cannot be determined without early dates
Correct Answer: A — Late start is day 14
Explanation: LS = LF - duration = 18 - 4 = 14. Early dates are not needed to compute LS from LF and duration.
