How float is calculated
The forward pass through the network gives each activity its earliest possible start and finish. The backward pass, working from the project completion or an imposed date, gives the latest start and finish that still permit that date to be met.
Total float is the difference: late start minus early start. Free float is narrower — it is the gap before the earliest of the activity's successors would be pushed, so it belongs to that activity alone and cannot be consumed by anything upstream.
This is why float is never a fixed property of an activity. Add a successor, change a calendar, apply a constraint, or record progress, and the float on that path changes with it.
Reading negative float
Negative float almost always means a constraint or an imposed completion date is earlier than the logic can deliver. Minus fifteen days on a chain means the network says you are fifteen working days short of the date you told it to hit.
Before treating it as delay, check the cause. A 'must finish on' constraint left over from an earlier revision produces negative float that has nothing to do with performance. A genuine slip on the driving chain produces the same number for a completely different reason. The DCMA check for hard constraints exists mainly to make this distinction possible.
Suspiciously high float
Total float above the profile limit — 44 working days under DCMA, 60 under AACE and USACE, or whatever you set for your project type — is usually missing successor logic rather than real slack. The activity is not tied into anything downstream, so the backward pass gives it an implausibly late date.
The practical consequence is that the critical path is understated: work that will in fact drive completion is sitting off the path because the network never connected it. Fixing open ends typically shortens float across the schedule and reveals a longer, more honest critical path.
Who owns the float?
Contractually this varies. Many standard forms and the SCL Protocol take the position that float is a project resource available to whichever party needs it first, rather than something owned by the contractor or the employer. Some contracts allocate it expressly, and some require float to be shown and maintained.
The analytical point is separate from the contractual one: track float trend across updates. A path whose total float erodes from thirty days to five over four months is the early warning that the eventual delay claim will be about.
Tracking float in TideLine
The Schedule module shows total float, negative float and the driving chain in the Gantt, with near-critical paths distinguished from the critical one so you can see which chains are one slip away from driving completion.
The Quality module tests float against the limits you set rather than a single fixed rule: high-float and negative-float thresholds come from the active profile — DCMA 14-Point, GAO, AACE RP-90R-19, NDIA PASEG or USACE/NAVFAC — and each metric's weight and warn/fail limits can be tuned to the project type, so a two-year fit-out and a ten-year infrastructure programme are not judged against the same numbers.
For float erosion over time, compare two schedules and open the result in the Delay module. Each window shows how dates and the critical path moved between the snapshots, and the root-cause view follows a late activity back up its dependency chain to where the float was actually consumed — early warning while there is still time to act, and evidence later if there is not.