Float (slack)
Float is the room a task has. It is the number of working days a task can start late, or take longer, before it pushes back the end of the whole plan. Tasks with no float at all form the critical path: if any of them slips, the finish date slips with it.
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Two tasks start together after a kick-off: "Write the content" takes 10 days and "Design the layout" takes 6. Both must finish before "Build the site" starts. The writing sets the pace, so it has no float. The design could start up to 4 days late, or take up to 4 days longer, and the build would still start on time: it has 4 days of float.
Total float and free float
- Total float: how far a task can slip before the end of the project moves
- Free float: how far a task can slip before the very next task has to move
- Zero float: the task is on the critical path
Why it matters
Float tells you where a delay is harmless and where it is not. When something has to give, take the time from a task with float. When a task with no float looks at risk, that is the one to watch, because nothing absorbs its delay. GanttCharts.app can highlight the critical path, the chain of tasks with no float, so the tasks that cannot slip stand out.
Frequently asked questions
What is float in a Gantt chart?
The number of working days a task can slip before it delays the end of the project. A task with zero float is on the critical path.
Is slack the same as float?
Yes. Slack and float are two names for the same idea. Some tools and courses use one, some the other.
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