Free float
Free float is the number of days a task can slip without delaying the earliest start of any task that depends on it. It is never more than total float, which measures the slip the project's finish date can absorb.
The difference matters when float is shared along a chain. A task can have plenty of total float and no free float at all: it cannot slip without pushing the next task, even though the chain as a whole has room before the finish date.
Free float is the safe amount to let a task slip without telling anyone downstream; total float is the most it can slip before the project is late.
Worked example
| Task | Duration | Depends on | Scheduled | Total float |
|---|---|---|---|---|
| 1. Plan | 3 days | None | Days 1 to 3 | 0 days |
| 2. Build | 6 days | 1 | Days 4 to 9 | 0 days |
| 3. Draft docs | 2 days | 1 | Days 4 to 5 | 2 days |
| 4. Review docs | 2 days | 3 | Days 6 to 7 | 2 days |
| 5. Release | 1 day | 2, 4 | Day 10 | 0 days |
Draft docs has 2 days of total float but 0 days of free float: Review docs starts the day after it finishes. Review docs has 2 days of free float, because Release also waits for Build.
Open this example in the free delay simulator to change the durations, the links or the delay and watch the schedule move.