Total float and independent float

Total float

Total float (TF) is the maximum time by which an activity can be delayed without delaying the completion of the project. It is shared with the other activities on the same path.

$$TF = LST - EST = LFT - EFT$$

Independent float

Independent float (IndF) is the time available for an activity when its predecessors finish at their latest time and its successors start at their earliest time. Using it affects no other activity, so it is the safest float.

$$IndF = \max\left(0,\ \min(EST_{succ}) - \max(LFT_{pred}) - D\right)$$

Example

Example network (days): A = 4 and B = 3 are start activities; C = 5 and D = 2 follow A; E = 3 follows C and D; F = 4 follows B. Project duration = 12 days.

Activity D: $TF = 9 - 6 = 3$ days. Its predecessor A is critical (LFT = 4) and its successor E starts at 9, so $IndF = 9 - 4 - 2 = 3$ days: D can move 3 days without affecting any other activity. Activity B: $TF = 8 - 3 = 5$ days but $IndF = 3 - 0 - 3 = 0$, since F starts as soon as B finishes; the float is shared with F.