Float vs Free Float vs Total Float: PMP Scheduling Mastery

Float: The Scheduling Concept That Defines the Critical Path

Float — also called slack — is the amount of flexibility an activity has within the project schedule. Understanding float is essential for the PMP exam because it is the mechanism that identifies the critical path, determines schedule risk, and informs resource allocation decisions. The exam tests three types of float, and confusing them is a common source of wrong answers.

Total Float

Total float is the amount of time an activity can be delayed from its early start without delaying the project completion date. It is the most commonly referenced type of float on the PMP exam.

Formula

Total Float = LS - ES (or equivalently, LF - EF)

Where LS = Late Start, ES = Early Start, LF = Late Finish, EF = Early Finish.

Key Points

• Activities on the critical path have zero total float — by definition.
• If an activity's total float is consumed (by delay or extended duration), the activity becomes critical.
• Total float is shared among activities on the same path. If Activity A and Activity B are sequential and share 5 days of total float, Activity A using 3 days of float leaves only 2 days for Activity B.

Free Float

Free float is the amount of time an activity can be delayed without affecting the early start of any immediately following successor activity. It is more restrictive than total float.

Formula

Free Float = ES of successor - EF of current activity (for finish-to-start relationships)

Key Points

• Free float is always less than or equal to total float.
• Free float belongs to the individual activity, not the path. Using free float does not affect any other activity.
• Most activities have zero free float. It typically only exists when multiple paths converge at a single successor node.
• An activity can have total float but zero free float — meaning it can be delayed without affecting the project end date but would affect the next activity's early start.

Project Float

Project float is the amount of time the project can be delayed without exceeding an externally imposed completion date. If the critical path duration is 45 days but the customer requires delivery in 50 days, the project float is 5 days.

Project float is less commonly tested than total and free float, but it appears in questions about imposed deadlines and contract dates.

Worked Example

Consider this network with activities A through F. All relationships are finish-to-start.

Path 1: A(3) → B(4) → E(2) = 9 days. Path 2: A(3) → C(6) → E(2) = 11 days. Path 3: A(3) → D(5) → F(3) = 11 days.

The critical paths are Path 2 and Path 3 (both 11 days). Activity B has total float of 2 days (11 - 9). But what about free float?

Activity B's successor is E. ES of E (via critical path through C) = 9. EF of B = 7. Free float of B = 9 - 7 = 2 days. In this case, total float and free float are equal because B's delay does not affect E's early start (E must wait for C anyway).

Why Float Matters Beyond Calculations

For the PMP exam, float is not just a math exercise. It informs project management decisions:

• Resource allocation: Activities with high float can lend resources to critical activities without schedule impact.
• Risk management: Activities with low float but high uncertainty represent significant schedule risk even if they are not on the critical path.
• Schedule compression: Understanding float helps identify which non-critical activities can absorb delays when crashing or fast tracking rearranges the schedule.
• Stakeholder communication: Float helps explain to stakeholders which delays matter and which do not.

PMP Exam Tips

1. When a question asks about delaying an activity without affecting the project, it is asking about total float.
2. When it asks about delaying without affecting any successor, it is asking about free float.
3. Total float is shared along a path; free float belongs to an individual activity.
4. Zero total float = critical path. Always.

Practice float calculations with step-by-step solutions in our PMP exam preparation platform.