Total Float vs Free Float: What’s the Difference?

Every network diagram question on the PMP exam eventually comes down to one thing: can you tell total float and free float apart under time pressure? They sound similar, the formulas look similar, and that’s exactly why PMI likes testing them. Get the definitions locked in, and the rest — critical path, schedule compression, near-critical paths — gets a lot easier.

This falls under the Process domain, which still carries the largest share of the exam even after the 2026 ECO update, so schedule float isn’t a topic you can afford to be shaky on.

Total Float

Total float (also called just “float” or “slack”) is how long you can delay an activity without pushing back the project’s finish date.

Formula:

Total Float = Late Start – Early Start

or equivalently:

Total Float = Late Finish – Early Finish

Every activity on the critical path has a total float of zero — that’s actually the definition of “critical.” Any activity with float above zero has some breathing room before it starts affecting the overall project deadline.

Free Float

Free float is narrower: it’s how long you can delay an activity without delaying the early start of the very next activity.

Formula:

Free Float = Early Start (next activity) – Early Finish (current activity)

Free float only comes into play when two or more activities converge into the same successor. If just one activity feeds into the next, its free float and total float will usually be identical. When multiple activities merge into one successor, only the non-critical one(s) among them will typically show a free float — the critical predecessor won’t.

A Worked Example

Say you have four activities:

Both B and C start right after A, and D can’t start until both B and C finish. Running the forward and backward pass:

The critical path here is A → B → D, and each activity on it has zero float, exactly as expected. Activity C, though, isn’t on the critical path — it finishes on day 6, but D can’t start until day 8 anyway (waiting on B). So C has one day of both total float and free float: you could delay it by a day and it wouldn’t push D’s early start or the project’s finish date.

A Note on Day-One Convention

You’ll see network diagrams number the first day as either “Day 0” or “Day 1.” Both are mathematically valid, but PMI’s own materials — and most PMP prep resources — use “Day 1” as the project start, since it reads more naturally (“today is day one,” not “today is day zero”). The formulas work out the same either way; just stay consistent within a single diagram so your Early Start and Late Start numbers don’t drift.

Total Float vs Free Float: Quick Comparison

Can Float Be Negative?

Worth knowing for the exam: if a project is already behind schedule or a hard deadline has been imposed earlier than the calculated finish date, total float can go negative. Negative float signals that the current plan can’t meet the deadline without compression (fast-tracking or crashing) — it’s a red flag PMI likes to test in scenario questions about schedule recovery.

Summary

Total float tells you how much slack an activity has relative to the whole project’s end date. Free float tells you how much slack it has relative to just the next activity. Every activity on the critical path has zero of both. When PMI asks you to calculate “the float” without specifying which type, default to total float — that’s the one they mean unless free float is explicitly named.

Keep advancing in your PMP journey — explore our other in-depth guides:

• Agile vs Waterfall: Which Methodology is Right for Your Project?
• The 5 Scrum Events Explained: Purpose, Attendees, and Effective Execution
• Why PMP Aspirants Fail? — And How to Avoid Them
• Confused Between Agile, Hybrid, and Predictive? Here’s a Clear Comparison
• Why You Should Track Your Errors — and How to Do It Right

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