Float (also called slack) is schedule cushion. Total float is how long an activity can be delayed without moving the project completion date. Free float is how long it can be delayed without delaying the very next activity. Activities with zero total float are on the critical path. Float is calculated by the CPM schedule from early and late start and finish dates.
Why it matters
Float is a shared, limited resource. When one trade burns it, the next trade inherits a tighter schedule. Who owns float is often defined in the contract (frequently “the project”), and that affects time extensions: a delay that only consumes float usually does not earn extra days.
Worked example
Illustrative: on Riverside Medical Center, painting a Level 2 corridor has 12 working days of total float. A 5-day slip uses 5 of those days; the job still finishes on time and the activity now has 7 days left. In contrast, the Level 3 fire damper install has zero float, so a 5-day slip there moves substantial completion 5 days.
Common mistakes
- Treating float as belonging to whoever uses it first.
- Padding activity durations to hide float, which makes the schedule less useful.
- Ignoring “near-critical” paths with only a few days of float.
How os.construction handles it
We’re building schedule views that can show remaining float next to the RFIs and submittals tied to each activity, so float erosion is visible early.