Total Float vs. Free Float: Formulas & Examples [2026]
A. Togay Koralturk, Best-Selling PMP Author
Last updated on September 15, 2026
10 min read
Two activities can each have "a week of slack," and delaying one is completely safe while delaying the other quietly pushes half your schedule. The difference is total float versus free float — the single distinction that separates project managers who understand a schedule from those who only read it. Get it wrong and you spend float you do not have; get it right and you know exactly which activities you can move and by how much. This guide explains total float vs free float in full — what each is, the formulas, a worked example that shows the two diverging, negative and zero float, and how both are tested on the PMP and CAPM exams.
What is float in project management?
Float — also called slack — is the amount of time an activity can be delayed before it causes a problem. It comes from the forward and backward pass of the critical path method, which gives every activity four dates: early start (ES), early finish (EF), late start (LS), and late finish (LF). The gap between when an activity can happen and when it must happen is its float.
The catch is that "before it causes a problem" has two meanings — before it delays the whole project, and before it delays the next activity — and those are not the same number. That is exactly why float splits into two types: total float and free float. Understanding both, and when they differ, is what lets you manage a schedule instead of just following it.
Total float: definition and formula
Total float is the amount of time an activity can be delayed from its early start without delaying the project's finish date. It is the most commonly used measure of schedule flexibility, and it is what most people mean when they say an activity "has float."
You calculate it from the dates the critical path method produces:
> Total float = LS − ES (or equivalently) LF − EF
If an activity's late start is day 8 and its early start is day 3, its total float is five days: you can start it anywhere in that window and still finish the project on time. An activity with zero total float has no room at all — it sits on the critical path.
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Free float: definition and formula
Free float is the amount of time an activity can be delayed without delaying the early start of any successor activity. It is a stricter, more local measure: it protects the next activity, not just the project's end date.
Its formula compares your activity to the one that follows it:
> Free float = ES of the next activity − EF of this activity
In words: take the earliest your successor can start, subtract the earliest your activity can finish, and the gap is how long you can slip before the successor has to move. Because free float only ever looks at the immediate successor, it is always less than or equal to total float — never more. An activity can have plenty of total float and still have zero free float, which is the single most important idea on this page.
Total float vs. free float
The difference comes down to what each one protects. Total float protects the project finish date and is shared by every activity along a path; free float protects the next activity's start and belongs to one activity alone. Here is the comparison at a glance:
| Total float | Free float | |
|---|---|---|
| Protects | The project's finish date | The early start of the successor activity |
| Formula | LS − ES (or LF − EF) | ES of next activity − EF of this activity |
| Belongs to | A whole path — shared among its activities | A single activity |
| Size | Larger (or equal) | Always ≤ total float |
| If you use it | Project still finishes on time | The successor's early start still holds |
The shared-versus-local point is the one that trips people up. When several activities sit on the same non-critical path, they share one pool of total float — if the first activity uses three days of it, the activities after it have three days less. Free float is what tells you whether spending that float will ripple into the next activity right away. The worked example below shows both numbers on the same schedule.
Worked example: total and free float
Consider a small network with two paths from start to finish. The critical path is A → B → D, taking 10 days (3 + 4 + 3). A parallel path, A → C → E → D, takes only 9 days, so the activities on it (C and E) carry float. After running the forward and backward pass, the dates and float work out like this:
| Activity | Dur | ES | EF | LS | LF | Total float | Free float |
|---|---|---|---|---|---|---|---|
| A (critical) | 3 | 0 | 3 | 0 | 3 | 0 | 0 |
| B (critical) | 4 | 3 | 7 | 3 | 7 | 0 | 0 |
| C | 2 | 3 | 5 | 4 | 6 | 1 | 0 |
| E | 1 | 5 | 6 | 6 | 7 | 1 | 1 |
| D (critical) | 3 | 7 | 10 | 7 | 10 | 0 | 0 |
Look at Activity C: its total float is 1 (LS − ES = 4 − 3), but its free float is 0, because its successor E starts on day 5 and C finishes on day 5 (ES of E − EF of C = 5 − 5 = 0). So C has a day of schedule flexibility for the project, yet delaying it at all immediately pushes E's early start. Activity E, by contrast, has total float 1 and free float 1 (ES of D − EF of E = 7 − 6 = 1) — it can absorb a full day without moving anything.
That one-day-of-total-float, zero-free-float situation on Activity C is the whole point. The total float of 1 is shared between C and E along their path; free float tells you that C cannot touch it without consequences, while E can.
Negative float and zero float
Two special cases round out the picture:
- Zero float: an activity with zero total float has no flexibility — it is on the critical path, and any delay to it delays the whole project. Finding the zero-float activities is finding the critical path.
- Negative float: float turns negative when an activity's late dates fall before its early dates, which happens when the schedule is already behind an imposed constraint or deadline — for example, a hard finish date set earlier than the network naturally allows. Negative float is a warning sign: it tells you the project is late against that constraint and by how much, so you know how much time you need to recover through schedule compression or rescoping.
In short, positive float is room to breathe, zero float is the critical path, and negative float is a deadline you are already missing.
Total float vs. free float on the PMP® and CAPM® Exams
On the PMP exam, float is tested two ways. The first is calculation: you may be given a network diagram or a table of ES/EF/LS/LF dates and asked for an activity's total or free float, so both formulas need to be second nature. The second, harder way is situational — a scenario where an activity has total float but little or no free float, and you must reason about what delaying it actually does. The exam rewards knowing that spending total float is safe for the project but can still shift a successor when free float is zero.
The CAPM tests the same material a little more directly, leaning toward the definitions and the two formulas, but the CAPM is scenario-based like the PMP, so expect at least one question that makes you apply the difference rather than just recite it. Both exams treat "float" and "slack" as synonyms, and both expect you to recognize zero total float as the critical path. Our PMP Complete Study Guide works through the forward and backward pass step by step so these numbers become quick and automatic under exam pressure.
PMP Practice Question: Total Float vs. Free Float
While updating the schedule, a project manager reviews Activity C: early start day 12, early finish day 15, late start day 18, late finish day 21. Its only successor, Activity D, has an early start of day 15. A resource conflict means the team wants to delay Activity C by 3 days, and the project manager must respond.
What should the project manager do?
a) Approve the 3-day delay without further analysis, since it fits comfortably inside Activity C's total float and the project's finish date is therefore protected.
b) Reject the delay, because Activity C's free float is zero and any slippage will therefore push out the project's completion date.
c) Approve the delay only after confirming that Activity D and the activities beyond it can absorb a 3-day shift in their early starts, then update the schedule and notify the affected owners.
d) Approve the delay and protect the plan by inserting a 3-day buffer after Activity D, drawn from the schedule reserve.
Correct answer: C.
Rationale: The floats must be computed before any judgment is possible. Total float = LS − ES = 18 − 12 = 6 days, so a 3-day delay cannot move the project's finish date and rejecting outright misstates the mechanics — that is choice b), which reads zero free float as project impact when it only ever threatens the successor. Free float = ES of D minus EF of C = 15 − 15 = 0 days, so the moment C slips, D's early start moves with it, consuming float shared down that path — which is what choice a) ignores by treating total float as if it were free float, the exact confusion this pair of formulas exists to expose. The correct response uses both numbers: the project is safe (total float 6), the downstream is not (free float 0), so confirm D and the path beyond it can absorb the 3-day shift, then replan and communicate. Choice d) spends schedule reserve on a risk that does not exist, since the finish date is already protected by float; reserves cover uncertainty, not a successor shift you can simply plan around. To drill questions where the calculation and the judgment both have to land, work through our PMP practice exams or, at the entry level, our CAPM practice exams.
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Frequently asked questions
What is the difference between total float and free float?
Total float is how long an activity can be delayed without delaying the project's finish date; free float is how long it can be delayed without delaying the early start of any successor activity. Total float is shared across a whole path, while free float belongs to a single activity, so free float is always less than or equal to total float.
How do you calculate total float and free float?
Total float = late start − early start (or late finish − early finish). Free float = the early start of the next activity − the early finish of the current activity. Both rely on the ES, EF, LS, and LF dates produced by the forward and backward pass of the critical path method.
Can free float be greater than total float?
No. Free float is always less than or equal to total float. Free float only measures the delay an activity can absorb before affecting its immediate successor, which is a subset of the delay it can absorb before affecting the whole project. If your numbers show free float exceeding total float, there is an error in the calculation.
Is float the same as slack?
Yes. "Float" and "slack" are interchangeable terms for the same concept — the amount of time an activity can be delayed. Total float is also called total slack, and free float is also called free slack. The PMP and CAPM exams use both words and treat them as identical.
What does zero float mean?
Zero total float means the activity is on the critical path: it has no flexibility, so any delay to it delays the entire project. Identifying the activities with zero total float is how you identify the critical path. Zero free float, separately, means any delay to the activity will push its successor's early start, even if the project end is still protected.
What is negative float?
Negative float occurs when an activity's late dates fall before its early dates, which happens when the schedule is behind an imposed constraint or deadline. It signals that the project is already late against that date and quantifies how much time must be recovered — through schedule compression or rescoping — to meet it.
Is total float vs. free float on the PMP exam?
Yes. Float is a core PMP scheduling topic. The exam tests both formulas through calculation questions on network diagrams and, more importantly, situational questions where an activity has total float but zero free float and you must reason about the effect of delaying it.
Is float on the CAPM exam?
Yes. The CAPM tests float within its predictive scheduling content, usually a bit more directly than the PMP — leaning on the definitions and the total and free float formulas — though the scenario-based format means you should still expect to apply the difference, not just recite it.
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