Total Float vs Free Float, With the Math

Total float vs free float comes down to what each number measures slack against. Total float is how many days a task can slip without delaying the project. Free float is how many days a task can slip without delaying the very next task. They come from the same schedule, use overlapping inputs, and are frequently confused because most PMs learn "float" as one number instead of two.

The direct answer: total float = Late Start minus Early Start (LS − ES), and it measures slack against the project end date. Free float = the successor's earliest start minus the task's own earliest finish (ES of successor − EF of task), and it measures slack against the very next task only. A task can carry real total float and still have zero free float, because the project end date is not the only thing a delay can threaten; the next task's start date is threatened first.

What Total Float Actually Answers

Total float answers "can this task slip without pushing out the project finish date?" It is the number every critical path calculation produces as a side effect: run a forward pass and a backward pass across the network, and total float falls out as LS minus ES for every task. A task with zero total float is, by definition, on the critical path. A task with 5 days of total float can run 5 days late and the project still finishes on time.

Total float is a project-level number. It does not care what happens to the tasks in between; it only cares whether the finish line moves.

What Free Float Actually Answers

Free float answers a narrower question: "can this task slip without delaying the task right after it?" The formula is the earliest start of the successor minus the earliest finish of the task itself. If a task has more than one successor, free float is the smallest of those values, because the tightest successor is the one that actually constrains the task.

Free float is local. It ignores the project end date entirely and only looks one step ahead. That makes it the earlier warning: a task can lose all of its free float and still not be on the critical path, but the moment it does, its successor's own schedule starts absorbing the delay instead.

The Worked Example: Where the Two Numbers Split

Take two non-critical tasks running in series, X then Y, that rejoin a critical task afterward. X starts on day 5 and takes 3 days (finishing day 8). Y starts right after X finishes, on day 8, and also takes 3 days (finishing day 11). The task they both feed into cannot start until day 14, which is where the 3 days of slack in this little chain actually lives.

Run the backward pass and both X and Y come back with 3 days of total float: neither one threatens the downstream task's day-14 start if the whole chain slips by up to 3 days. Free float is where they split. X's free float is the earliest start of its own successor, Y, minus X's earliest finish: day 8 minus day 8, which is zero. X cannot slip at all without immediately pushing Y's start later, even though the project itself would not notice for another 3 days. Y, sitting right before the merge, keeps the full 3 days as free float, because nothing sits between Y and the point where that slack is measured. The full network diagram and forward/backward pass for a complete schedule live in the CPM guide, for a worked example that carries all the way through a critical path calculation.

Total Float vs Free Float at a Glance

	Total Float	Free Float
Answers	Can this slip without delaying the project?	Can this slip without delaying the next task?
Formula	LS − ES (or LF − EF)	ES of successor − EF of task
Reference point	Project finish date	The task's own immediate successor
Zero means	Task is on the critical path	Task's slip touches its successor right away
Can differ within a chain	Shared across a chain of non-critical tasks	Belongs to each task individually
Which is larger	Always greater than or equal to free float	Always less than or equal to total float
Best used for	Identifying the critical path	Spotting the earliest local warning sign

Which One Should You Track Week to Week

Total float tells you whether a task is critical. Free float tells you whether a task is about to start causing trouble for its neighbor, before that trouble has any chance of reaching the project end date. A PM who only watches total float will miss the moment a non-critical task starts squeezing the task after it; a PM who only watches free float will miss slower, chain-wide erosion that eventually removes all the slack from a whole sequence of tasks at once. Track both by hand on a small schedule, or run the free Schedule Health Check against an .mpp file to get both numbers computed directly from the real dependency graph instead of a manual pass. Schedule buffer management covers how to size the reserve that absorbs this erosion before it reaches zero, and dependency types covers how the wrong dependency type can shrink both numbers without anyone changing a single duration. Both posts sit alongside this one in the wider scheduling fundamentals library.

Check your schedule's real float numbers Upload an .mpp or MSPDI XML to the free Schedule Health Check and get total float, free float, and the actual critical path computed from your dependency graph, not a rough manual estimate. No signup, no credit card. → Run the Schedule Health Check