Float (Total Float and Free Float)

Float — sometimes called slack — is the scheduling concept that tells you how much flexibility exists around an activity. Total float is the amount of time an activity can slip before it delays the project end date (or a key contractual milestone). Free float is the smaller number: how much the activity can slip before it delays its immediate successor. An activity on the critical path has zero total float — any delay to it directly delays the project. Activities with plenty of float are the ones you can deprioritise when resources are scarce.

Float is a key input to resource management, risk assessment, and schedule compression decisions. When reviewing a schedule, negative float (where activities would need to start in the past to meet the end date) is a clear sign that the programme is unrealistic and needs either compression or a revised end date. Near-critical paths — those with small positive float — are important to monitor because they can easily become critical as the project progresses. In a risk-modelled schedule, the criticality index (the proportion of Monte Carlo iterations in which an activity appears on the critical path) is more informative than deterministic float alone.

Float ownership can be a source of commercial tension on contracts, particularly where the contractor and client both believe they have a right to use available float. NEC and other standard form contracts have specific provisions on this. A practical rule of thumb: total float belongs to the project, not to any individual activity owner. Managing float as a shared resource — and being transparent about how near-critical paths are trending — is part of good programme governance. Be wary of schedules where all activities show the same float: this is usually a sign that constraints have been applied to force dates rather than that the logic actually supports them.