project management glossary

free float

 The maximum amount by which an activity can be delayed beyond its early dates without delaying any successor activity beyond its early dates.

 The amount of time (in work units) an activity may be delayed without affecting the early start of the activity immediately following.

 The excess time available before the start of the following activity, assuming that both activities start on their early start date. Free float is calculated in the following way: Free Float = Earliest Start of Following Activity - Earliest Start of Present Activity - Duration of Present Activity. On the activity's calendar, free float is the length of time from the end of the activity to the earliest early start date from among all of its successors. If the activity has no successors, the project finish date is used. Since free float is meaningless for hammocks, it is set to zero. For the common case where all lags are finish-to-start lags of zero, the free float represents the number of work days that an activity can be delayed before it affects any other activity in the project.

 The delay possible for an activity if all preceding activities start as early as possible whilst all subsequent activities also start at their earliest time - an equivalent (and easier) definition is the delay possible in an activity if it starts at its earliest time and all subsequent activities start at their earliest time. The effect of this free float is to push the total float associated with a chain of successive non-critical activities onto the last activity in the chain.

 See also Float.