Both Total Float and Free Float are very important values in Primavera. The planning engineer should keep an eye on both Float types, so that decision making becomes quicker and easier if anything needs to be changed in the plan.
Let's learn what Total Float and Free Float are in Primavera.
By definition Total Float is ""number of days an activity can be delayed without delaying project finish date"". Let's understand Total Float more with an example:
Activity A Finish Date: 10 March. Project Must Finish Date (Deadline) is 20 March. Activity A can be delayed until 20 March, hence delay of 10 days. So, Total Float for Activity A is 10 days.
Activity B Finish Date is 15 April. Project Must Finish Date is 15 April. We can see that Activity B can not be moved forward as it is already finishing on last day of project. So, Total Float of Activity B is 0 days.
Total Float of an activity can be dependent on Total Float of another activity, if both are linked with each other. For example:
Activity A --> Activity B (Linked with Relationship)
Total Float of Activity B is 0 days. So, Total Float of Activity A is also 0 because if it moves forward, it will move Activity B forward, hence Activity A can't be moved. Put another way, the activities are linked, the Total Float of an Activity is the same of the last linked activity.
It is number of days an activity can be delayed without delaying the successor activity. An activity, when linked with another activity always has 0 Free Float because if it moves, it will also move its success activity. An activity can have more than 0 Free float if it is not linked with any successor activity, so its Free Float will by number of days this activity can be delayed until project finish date. An activity can have more than 0 Free Float also in case when the activity has more than one successor and lag between of the successor activities is longer than the other. In this case, where there is less lag between the activities, the activity will have more than 0 Free Float.
Remember that Float is also called Slack. If you use Microsoft Project, there is no word Float in there, instead the word Slack is used.