Float

Float, or slack, is the amount of time an activity can be delayed without delaying something else. It is computed by the critical path method. A forward pass through the network gives each activity's earliest start (ES) and earliest finish (EF); a backward pass from the project end gives latest finish (LF) and latest start (LS).

Total float is LS − ES (or LF − EF): how long an activity can slip without delaying project completion. Activities with zero total float form the critical path, the longest path through the network, which sets the project duration. Free float is how long an activity can slip without delaying the earliest start of any successor; it is never more than total float. Independent float, rarely used, assumes predecessors finish late and successors start early. Negative float appears when a constraint date cannot be met with the current logic, showing how far behind the plan is.

Float is a shared resource along a path: if one activity uses it, later activities on the same path lose it. Who owns float is a common contract question; many contracts treat it as belonging to the project, available to whoever needs it first, while some reserve it. Near-critical paths with small float deserve as much attention as the critical path, because a small delay can make them critical. In delay analysis, float determines whether an event actually delayed completion.