Plan and manage schedule
Plan and manage schedule
What you will learn
- Distinguish total float from free float.
- Compute a three-point (PERT) estimate from optimistic, most-likely, and pessimistic estimates.
- Understand why the critical path has zero total float.
- Connect the float concept to deciding which task can slip without affecting the project's end date.
Knowing the critical path alone isn't enough to manage a schedule professionally — the everyday practical decision is: which task can slip a little without delaying the whole project? That's exactly what float answers, in its total and free forms.
Total float vs. free float
| Total Float | The maximum a task can slip without delaying the project's overall end date. Critical-path tasks always have zero total float. |
|---|---|
| Free Float | The maximum a task can slip without delaying the start of the very next task after it. Its value is always less than or equal to that task's own total float. |
Three-point (PERT) estimating
Optimistic (O)
The best-case scenario with no obstacles.
Most Likely (M)
The most realistic estimate under normal conditions.
Pessimistic (P)
The worst reasonable scenario with real obstacles.
The weighted (Beta) formula
Final estimate = (O + 4M + P) ÷ 6 — gives the most-likely estimate greater weight.
What matters on the exam
- A calculation question with three values (optimistic, most likely, pessimistic) expects (O + 4M + P) ÷ 6 unless stated otherwise explicitly.
- A critical-path task's total float is always zero; any other number in the question means the task isn't on the critical path.
Free float is not a synonym for total float
A common trap: assuming "float" is one single concept. A task might have 5 days of total float (won't delay the project) while its free float is only 2 days (will delay the very next task's start if exceeded) — the two numbers differ because they measure two different effects.
Quick check
Answer in your head first, then reveal.
What is the total float of any task on the critical path?Reveal the answer
Zero.
What is the weighted three-point estimating formula?Reveal the answer
(Optimistic + 4×Most Likely + Pessimistic) ÷ 6.
What is the difference between total and free float?Reveal the answer
Total measures allowed slip without delaying the project; free measures allowed slip without delaying the immediate next task's start.
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Sources
Used to verify the facts. The writing is original to Passuit.