Critical Path Calculator
Enter tasks with durations and dependencies to get the critical path, project duration, early and late start dates and the float available on every non critical task.
Last reviewed by the Radiatus Cloud team
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The longest path sets the date
A project finishes when its longest chain of dependent tasks finishes. That chain is the critical path, and every task on it has zero float: delay any of them by a day and the project slips by a day. Tasks off the critical path have float, meaning they can slip by some amount before they affect anything. Knowing which tasks are which is the difference between managing a project and reacting to it, because it tells you exactly where attention is worth spending.
Float is the number people want
Total float is how long a task can be delayed without moving the project end date. Free float is how long it can be delayed without affecting any successor task, which is usually smaller. A task with fifteen days of total float and two days of free float will not delay the project, but delaying it more than two days will push a dependent task, which matters if that task needs a specific resource. The calculator reports both, since managing to total float alone is how a project accumulates a queue of newly critical tasks.
Near critical paths are the real risk
A path one day shorter than the critical path is not safe; it is one bad day from becoming critical. Projects rarely fail because the critical path slipped in a way anyone could have predicted, they fail because three near critical paths all slipped slightly and one overtook. This tool highlights paths within a configurable threshold of critical, because those are the ones worth watching and the ones a single critical path view hides.
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Frequently Asked Questions
What is total float versus free float?
Total float is how long a task can slip without delaying the project. Free float is how long it can slip without delaying any immediate successor. Free float is always less than or equal to total float, and it is the one that matters for resource scheduling.
What makes a task critical?
Zero total float. Its early start equals its late start, so any delay propagates straight through to the project end date. There is always at least one critical path, and there can be several of equal length.
Why does my project have more than one critical path?
Because two or more chains happen to be the same length. This is common and it makes the project more fragile, since a delay on either chain moves the end date. Parallel critical paths deserve more attention, not less.
What is a near critical path?
A path whose length is close to the critical one. A path with two days of float on a six month project is effectively critical, because two days of slippage is routine. Watching only the strictly critical path is how projects are surprised.
Does this account for resources?
No. The critical path method assumes unlimited resources and calculates the logical minimum duration. If two parallel tasks need the same person, the real schedule is longer. That is resource levelling, which is a separate and harder problem.
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How to Use
Add tasks with a duration and the tasks they depend on, then read the critical path and float.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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