What is the difference between free float and total float?

Total float is the amount of time an activity can be delayed without delaying the project end date. Free float is the amount of time an activity can be delayed without delaying the early start of any successor activity. An activity can have total float but zero free float if delaying it would delay a successor even though it would not delay the project. Critical path activities have zero total float by definition. Free float is always less than or equal to total float. The PMP exam tests both concepts and expects candidates to distinguish between them in scheduling scenarios.