P6 Float Calculator
What is a P6 Float Calculator?
What is P6 Float?
Float (or slack) is the operational flexibility in a Critical Path Method (CPM) network. Total Float measures project finish impact, while Free Float measures immediate successor impact.
Formula
Total Float (TF) = Late Start (LS) - Early Start (ES) = Late Finish (LF) - Early Finish (EF)
Free Float (FF) = Early Start of Successor - Early Finish of Current Activity
Variables Explanation
- ES & EF: Early Start and Early Finish dates derived from forward pass.
- LS & LF: Late Start and Late Finish dates derived from backward pass.
- Next ES: Early Start of the immediate successor activity.
How to Calculate
1. Enter Early Start (ES) and Early Finish (EF).
2. Enter Late Start (LS) and Late Finish (LF).
3. Input Early Start date of immediate successor task.
4. Review Total Float, Free Float, and Critical Path classification.
Worked Example
Current Task (Steel Fabrication): ES = Day 10, EF = Day 18, LS = Day 14, LF = Day 22.
Successor Task (Erection): Next ES = Day 20.
Total Float = 14 - 10 = 4 Days.
Free Float = 20 - 18 = 2 Days.
Interpretation: Task can delay 2 days without affecting Erection, or 4 days without delaying project completion.
Practical Construction & Project Controls Use
Used by delay analysts for Extension of Time (EOT) claims, resource smoothing, and risk mitigation in construction scheduling.
Understanding the Result
Total Float = 0 indicates a Critical Path activity. Negative float indicates a compromised constraint date requiring schedule acceleration.
Limitations & Assumptions
Calculates float based on user-entered dates. In complex P6 networks with lags or start-to-start relationships, float path analysis should be verified.
Frequently Asked Questions
What is Total Float in Primavera P6?
Total Float is the maximum time an activity can be delayed from its Early Start without delaying the project finish date.
How does Free Float differ from Total Float?
Free Float is the delay allowed without affecting the Early Start of any immediate successor activity.
Why does Primavera P6 show negative float?
Negative float occurs when a hard Must Finish By constraint date is earlier than the calculated CPM Early Finish date.
Does zero float always mean an activity is critical?
In standard CPM networks without constraints, activities with Total Float = 0 constitute the Critical Path.
Who owns the float in a construction contract?
Contract terms vary, but generally float belongs to the project as a shared resource unless explicitly stated otherwise.