Lessons · Project management · float
Float: how much an activity can slip before the end date moves
Total float is late start minus early start (equally, late finish minus early finish); it is the slack an activity has before it delays the project.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
The Friday the date slipped, the question was which activity had used up its float. An activity with 2 days of float that slips 3 has moved the end date by 1, and it did so quietly, because nobody was watching a number they had not calculated.
How to think about it
After both passes, subtract for each activity: float = LS − ES. Zero means no room. Write the float next to the activity and re-check it whenever something slips; float is spent, and what is spent is gone.
Worked example
C: ES 3, LS 5, float = 5 − 3 = 2 daysC can start up to two days late and the project still finishes at day 12.
B: ES 3, LS 3, float = 0No room. A day late on B is a day late on the project.
C slips 3 daysTwo days were float; the third moves the end date to day 13.
Your turn
An activity has ES 4 and LS 9. Write its total float.
float = 9 − = 5 days
Solve one, graded on the server
The trap
Treating float as belonging to one activity. Activities on the same path share it: if C uses its two days, the activity after C has none left.