What Is Float in a Construction Schedule?
By Wyatt Cooper · Published · 4 min read
Key takeaways
- Total float is how long an activity can slip without moving the project's finish; free float is how long it can slip without moving the next activity.
- Activities on the critical path have zero total float; negative float means the schedule already misses a required date.
- Many contracts say the float belongs to the project, so whoever needs it first, owner or contractor, can use it.
Float (also called slack) is the number of working days an activity can be delayed. Total float is the delay it can take without moving the project's finish date; free float is the delay it can take without moving the early start of any activity after it. Critical-path activities have zero total float.
Total float and free float on one network
Five activities on a made-up slab job, in working days, linked finish-to-start: excavate (A, 3 days); footings (B, 5 days) and underground plumbing (C, 2 days) after A; the under-slab inspection (D, 1 day) after C; the slab (E, 2 days) after B and D. The job takes 10 days. Total float is late finish minus early finish; free float is the earliest early start of the activities after it, minus its own early finish.
| Activity | Early start–finish | Late start–finish | Total float | Free float |
|---|---|---|---|---|
| A Excavate (3) | 0–3 | 0–3 | 0 | 0 |
| B Footings (5) | 3–8 | 3–8 | 0 | 0 |
| C Plumbing (2) | 3–5 | 5–7 | 2 | 0 |
| D Inspection (1) | 5–6 | 7–8 | 2 | 2 |
| E Slab (2) | 8–10 | 8–10 | 0 | 0 |
C and D share the same 2 days of float. If the plumbing (C) slips one day, the inspection (D) moves a day too, because C has no free float, but the slab still starts on time. If the inspection alone slips two days, nothing else moves: its free float covers it. A third day on either one moves the finish to day 11. That is why the critical path is the chain to watch, and the float on the chain next to it the second.
Negative float and who owns the float
Microsoft's Total Slack field page notes that total slack can be negative: the time that must be saved so the finish is not delayed. That is what a schedule shows when its finish is held to a contract date it can no longer make. The Free Slack page defines free slack as the delay a task can take "without delaying any successor tasks".
Who may spend the float is a contract question. The Army Corps of Engineers' UFGS 01 32 01.00 10 says float "belongs to the Project" and is available to both the contractor and the government, and it forbids artificial constraints such as "zero free float". Private contracts vary, so check yours before you plan to use float as your own cushion.
How it works in Conflo
Conflo's schedule calculates total float in working days on the project's calendar, measured against the latest finish on the schedule, and marks tasks with none as critical. It doesn't calculate free float, and because float runs to the schedule's own finish rather than to a contract date, it doesn't show negative float: a slipping finish shows as variance against the baseline instead.
The bottom line
Total float protects the finish date; free float protects the next crew. Read both before you let an activity slide.
Read your contract's float clause before you treat float as yours, and mark the zero-float work on your three-week look-ahead so the field sees it.
Sources
- UFGS 01 32 01.00 10, Project Schedule (August 2026), §3.3.8 and §3.10 Ownership of Float — U.S. Army Corps of Engineers (Whole Building Design Guide). Read October 16, 2026.
- Total Slack (task field) — Microsoft Support. Read October 16, 2026.
- Free Slack (task field) — Microsoft Support. Read October 16, 2026.
Questions
Is float the same as slack?
Yes. Primavera P6 and most specifications say float; Microsoft Project calls the same numbers total slack and free slack.
Can free float be more than total float?
No. Free float is at most total float, because a delay that moves the finish date also moves whatever follows the activity, or is the finish itself.
What does negative float mean?
The schedule's logic and durations can't meet a constrained date, usually the contract completion date. The number is how many working days must be recovered on that path.
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