⏱️ Late Start (LS) & Late Finish (LF) in Microsoft Project

Late Start and Late Finish tell you the last safe moment a task can start/finish without delaying the project’s final finish date (CPM logic).

CPM (Critical Path Method) Schedule flexibility Float / Slack Construction-ready meaning

✅ What LS & LF mean (simple)

In Microsoft Project, Late Start (LS) and Late Finish (LF) answer this: “How late can this task move without pushing the project end date?”

Late Start (LS)
The latest date a task can start without delaying the project finish.

“How long can I wait before starting this task?”

Late Finish (LF)
The latest date a task can finish without delaying the project finish.

“How late can I finish this task safely?”

Important: If a task starts after LS or finishes after LF, you risk a project delay (finish date slips).

🖼️ Visual references

Microsoft Project Late Start Late Finish columns example — Example view of late dates in scheduling.

Critical path late dates diagram — Late dates used in CPM backward pass.

CPM schedule float illustration — Float/Slack concept linked to LS/LF.

Float example diagram — How float creates safe movement window.

🔹 1) Late Start (LS)

Definition: The latest date a task can start without delaying the project finish.

If a task starts after its Late Start, the task is eating more than its allowed float and can push the project end date.

Memory idea: “How long can I wait before starting this task?”

🔹 2) Late Finish (LF)

Definition: The latest date a task can finish without delaying the project finish.

If a task finishes after its Late Finish, the project completion date can slip.

Memory idea: “How late can I finish this task safely?”

🧮 Relationship (easy formula)

Late Finish (LF) = Late Start (LS) + Task Duration Late Start (LS) = Late Finish (LF) − Task Duration

Tip: Think of LS/LF as the “backward plan” dates (calculated from the project finish date backward).

📊 Simple example

Task	Duration	Late Start	Late Finish
Foundation	5 days	Day 10	Day 15

👉 This means:

You can start as late as Day 10
You must finish by Day 15
Starting on Day 11 → ❌ risk of project delay

🟥 Critical Path connection (very important)

Critical tasks

Early Start = Late Start
Early Finish = Late Finish
Total Float = 0

Non-critical tasks

Late dates are later than early dates
Positive float (slack)
Can be moved safely (within float)

Site mindset: Critical tasks are “no delay allowed.” Non-critical tasks are “can move a bit” — but only up to LS/LF.

🔍 Why LS & LF matter (construction / engineering use)

🛠 Reschedule safely without delaying handover
👷 Move labor & resources to urgent tasks
⚠️ Identify risky tasks with very small float
📈 Recover delays using float wisely (crash/fast-track only when needed)

One-sentence memory trick:
Early = soonest possible
Late = last safe moment

📌 Next steps (tap to open)

Where do I show Late Start (LS) and Late Finish (LF) in Microsoft Project?

In a Task Sheet view, right-click any column header (like “Start” or “Finish”) → Insert Column → search for Late Start and Late Finish → insert them.

LS/LF vs Float vs Slack — what’s the difference?

LS/LF = last safe dates (schedule boundaries)
Total Float (Slack) = how much a task can slip without delaying the project finish
If Total Float = 0 → task is critical (no safe slip)

How do I use LS/LF to recover a delayed construction schedule?

Check tasks with small float (near-critical) and protect them.
Move resources from tasks with larger float to the urgent ones.
Use crashing (extra labor/overtime) only on tasks that affect the finish date.
Use fast-tracking carefully (overlap tasks) where quality risk is acceptable.

Want me to add a construction mini-case (foundation → columns → slab → walls → roof) and show exactly how LS/LF + float control manpower? Tell me your sample durations and I’ll build it.

✎ Edit Post ↑ Top Up

Late Start (LS) & Late Finish (LF) in Microsoft Project