Float (Total Float)

How it is computed

Total float = latest start (LS) - earliest start (ES); the same value falls out of LF-EF. A task with ES on day 6 and LS on day 9 has three days of float: it can start up to three days late without touching the project finish. Zero float means the task sits on the critical path. Where deadlines or fixed start dates collide with the logic, float can drop below zero — negative float is not a record of late execution — it is a warning that the constraint date cannot be met with the current logic and durations. Float is most useful read at the leaf-task level, where the work actually happens — summary-level float flattens the situations of all descendants into an illusion.

Why it matters

Float is the evidence behind resource decisions. Pulling a person off a high-float task to reinforce the critical path is only safe when the float number says so. When the schedule starts slipping, the float distribution is the answer to "what can we touch, and what must we not." It sharpens reporting too: "two days of float left" sets both the size and the urgency of the response in a way "we are late" never does. The trend matters too: a path whose float shrank from five days last week to two this week is a problem in the making, even before it turns critical.

Common misconceptions

Treating float as the task's private property is the misconception. Float is shared along a path: when an upstream task consumes it, downstream tasks lose exactly that much. The habit of delaying starts "because there is float" — student syndrome — is the quiet way to burn a whole path's cushion. Remember, too, that float is counted in working days: three days of float is not the same as three calendar days.