Total float is the amount of time an activity can slip without delaying the project finish (or a date imposed on the schedule, such as a constraint or must-finish-by date). In a simple network on one calendar, Late Start − Early Start gives the same answer as Late Finish − Early Finish. With multiple calendars, constraints or in-progress work the two can differ, which is why P6 lets you choose which to use. Drag the slider below to see it happen live.
Total float vs free float
Total float is measured against the whole project finish — how much X can slip before the project finish date moves. Free float is narrower: how much X can slip before it delays its own immediate successor, ignoring the rest of the network. An activity can have zero free float (its very next successor is tight against it) while still carrying total float, if float reappears further down the chain.
Float belongs to the path, not the activity
Float isn't really a property of one activity — it's shared across every activity on that non-critical path. If one activity on a float path uses up float (runs long), activities sharing that path lose float too; where paths branch and merge the amounts can differ.
Negative float
When an activity's Late Start comes before its Early Start, total float goes negative. That only happens when a date is imposed on the network — a constraint or a project must-finish-by date. The visualiser holds End at day 10, so dragging the slider past 10 shows negative float; without an imposed date, P6 would simply move the project finish later. Negative float means the network, as logically linked, cannot meet the imposed date: work needs to be resequenced or compressed, or the target date needs to move.
High float as a warning sign
The DCMA 14-point assessment includes a high-float check: it counts incomplete activities with more than 44 working days of total float, with a commonly cited target that no more than 5% of incomplete activities exceed it. High float is not wrong in itself, but it is worth reviewing because it can point to missing or incorrect successor logic rather than genuine flexibility.
Why the float type setting matters
P6's schedule options let you compute total float as start float (LS − ES), finish float (LF − EF) or the smaller of the two, and other options (such as how progressed activities are scheduled and whether float is calculated against each project's own finish) also affect the result. That is why two schedulers can schedule the same XER with different options and get different float for the same activities. When comparing a contractor's schedule against your own recompute — or comparing float across two organisations' schedules — mismatched float settings are a common, easy-to-miss source of "wrong" numbers that are actually just computed differently.
An unexplained jump in an activity's total float between two updates is worth investigating before it becomes a dispute. Compare logic, durations, constraints, calendars, progress and scheduling options on the activity and on the paths around it. The schedule data shows that float moved and which inputs changed; it cannot by itself tell you why.
DCMA float checks → dcma.html