Total float
Total float, also called slack, is the number of days a task can slip without moving the project's finish date. Tasks on the critical path have zero total float.
It is calculated as the latest a task can start minus the earliest it can start (or the same for finish dates), from a forward and a backward pass through the network.
Total float belongs to a chain, not only a task: tasks in a row share it, so if the first uses some, there is less left for the rest.
Worked example
| Task | Duration | Depends on | Scheduled | Total float | After the delay |
|---|---|---|---|---|---|
| 1. Plan | 3 days | None | Days 1 to 3 | 0 days | Unchanged |
| 2. Build | 5 days | 1 | Days 4 to 8 | 0 days | Unchanged |
| 3. Write docs | 2 days | 1 | Days 4 to 5 | 3 days | Days 4 to 9 |
| 4. Release | 2 days | 2, 3 | Days 9 to 10 | 0 days | Days 10 to 11 |
The delay: Write docs takes 4 days longer.
Write docs has 3 days of total float. A delay of 4 days uses all of it and passes the remaining 1 day on: Release now finishes on day 11 instead of day 10.
Open this example in the free delay simulator to change the durations, the links or the delay and watch the schedule move.