Total Float

Total float — sometimes called total slack — is calculated from the difference between the latest allowable finish date (from the backward pass through the network) and the earliest possible finish date (from the forward pass). An activity with zero total float is on the critical path; delay it and the project end date moves. An activity with, say, 15 days of total float can slip up to 15 days before it starts affecting the project completion date. Total float is a property of a chain of activities, not of a single task in isolation — using float on one activity in a chain reduces the float available to every downstream activity on the same path.

Total float is one of the most important indicators a planner or project controls engineer works with. It tells you where the real risks to the programme are, where you can afford to deprioritise resources when they are under pressure, and where a delay is consequential. On a busy project with multiple competing demands, float is a resource that needs managing just like labour or equipment. If you allow float to drain away on near-critical paths without noticing, you wake up one day with several paths simultaneously critical and no good options left.

Two practical cautions. First, total float belongs to the project, not to any individual activity or subcontractor. A contractor who treats the float on their activities as private scheduling headroom is consuming a project resource they do not own. NEC contracts address this explicitly through the float allocation provisions and the Accepted Programme process. Second, schedules where most activities show the same float value — for example, every task shows exactly 10 days — are usually constrained rather than logic-driven: someone has applied a target date and allowed the tool to back-calculate the appearance of float rather than letting the logic run. Treat that kind of uniformity with suspicion.