According to the PMBOK Guide, Free Float (FF) is defined as the amount of time that a schedule activity can be delayed without delaying the early start date of any successor or violating a schedule constraint.
* Calculating Free Float: The formula for Free Float is:
$$FF = ES_{successor} - EF_{activity} - 1$$
(Note: The " -1 " is used if using the " Day 1 " start convention; if using " Day 0 " , it is simply $ES - EF$).
* Analysis of the Network Diagram (Standard PMI Question Set 259-261):
In the standard diagram for this specific question sequence:
* Activity H and Activity G are parallel paths leading into the final Activity I.
* The Critical Path usually runs through Activity G (A-B-C-F-G-I), meaning Activity G determines the Early Start (ES) for Activity I.
* If Activity I has an Early Start of Day 31, and Activity H finishes on Day 20, then Activity H has
10 days of " Free Float " because it can slip until Day 30 without pushing the start of Activity I.
* Free Float vs. Total Float: Unlike Total Float (which is the delay allowed without delaying the project finish date), Free Float is strictly concerned with the immediate successor. In this diagram, since Activity H is the last activity before the final node, its Free Float often equals its Total Float, provided there are no other constraints.
Comparison with other options:
* A and B (4 or 5 days): These numbers typically represent the duration of individual activities or the float of a different path (like the D-E path) rather than the specific buffer available for Activity H.
* D. 11: This is often a result of a calculation error where the finish day of the activity is subtracted from the start day of the successor without accounting for the inclusive nature of the workday (the " off-by- one " error). In PMI standards, if an activity finishes on the evening of Day 20, and the next starts on the morning of Day 31, there are exactly 10 full days of float (Days 21 through 30).