Calculator
CPM project management calculator — critical path, Malaysia
Enter your tasks, how long each takes and what it waits on. It runs the forward and backward pass, works out the float on every task, and shows which ones actually set your finish date.
| ID | Task | Days | Depends on | ES | EF | LS | LF | Float |
|---|---|---|---|---|---|---|---|---|
| 0 | 5 | 0 | 5 | critical | ||||
| 5 | 13 | 5 | 13 | critical | ||||
| 5 | 20 | 8 | 23 | 3 | ||||
| 13 | 23 | 13 | 23 | critical | ||||
| 23 | 27 | 23 | 27 | critical | ||||
| 27 | 33 | 27 | 33 | critical |
33 days
Shortest possible duration. The highlighted rows have zero float and form the critical path — delay any of them and the finish date moves by the same amount.
What the numbers mean
ES and EF — earliest start and earliest finish. The forward pass: a task can start as soon as everything it depends on has finished, so ES is the latest EF among its predecessors, and EF is ES plus the duration.
LS and LF — latest start and latest finish without pushing the project out. The backward pass works from the end date back, so LF is the earliest LS among the tasks that follow, and LS is LF minus the duration.
Float — LS minus ES. It is how long a task can slip before it costs you the finish date. A task with zero float is on the critical path, and a day lost on it is a day lost on the project.
The practical use is not the diagram, it is the conversation it ends. When someone asks for two more weeks on a task with eleven days of float, the answer is different from the same request on a critical task — and without the float figure, both requests sound the same.
Where the critical path stops helping
It assumes your durations are right. Most schedule overruns in practice are not a network problem — they are an estimating problem, where effort was recorded as duration and nobody accounted for the fact that the people doing the work have other jobs.
It also ignores resource constraints. Two tasks with plenty of float can still collide if the same person has to do both, and the network will not tell you that.
And it says nothing about the decisions ahead of the work. On most real projects the item that sets the finish date is an approval or a long-lead order that nobody put on the network at all, because it did not look like a task.
Questions
›What is the critical path?
The longest chain of dependent tasks through a project. It sets the shortest time the project can possibly take, and every task on it has zero float.
A project can have more than one critical path, and the critical path can move during delivery as actual durations change.
›What is float, and how is it different from buffer?
Float is calculated — it falls out of the network as the difference between when a task can start and when it must start. Buffer is added deliberately, as contingency.
Confusing the two is common and expensive: teams consume float believing it was reserved for them, when it was simply an artefact of the sequence and belonged to whoever needed it first.
›Why does the calculator say some tasks could not be scheduled?
Usually a circular dependency — two tasks each waiting on the other — or a predecessor ID that does not match any task.
Check the "Depends on" column against the IDs in the first column. IDs are matched case-insensitively and can be separated by commas or spaces.
›Does this replace scheduling software?
No. It is a fast way to see the shape of a dependency network and find the tasks that actually govern the date, which is useful in a planning session or when sanity-checking a plan someone hands you.
For a live project with resources, calendars and baselines you want proper scheduling software.
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