Critical Path Method Calculator
Enter your tasks, durations, and dependencies to compute the critical path, total project duration, earliest/latest start & finish, and float. Supports PERT three-point estimates. Runs entirely in your browser.
About this tool
The Critical Path Method (CPM) turns a list of tasks — each with a duration and a set of predecessors that must finish first — into a full project schedule. This calculator runs the standard forward and backward passes to find:
- the total project duration (the length of the longest dependency chain),
- the critical path — the sequence of tasks with zero slack, where any delay pushes out the whole project,
- and, for every task, its earliest start / finish, latest start / finish, total float (slack) and free float.
Everything runs locally in your browser — no accounts, no uploads.
Input format
Enter one task per line as name, duration, predecessor, predecessor, ...:
A, 3
B, 4, A
C, 2, A
D, 5, B, C
E, 1, D
duration is a plain number, or a PERT three-point estimate
optimistic/most-likely/pessimistic such as 2/4/9, which is reduced to the
expected time (o + 4·m + p) / 6. Blank lines and lines starting with # are
ignored.
Worked example
For the five tasks above, the tool reports a project duration of 13 and a
critical path of A -> B -> D -> E. Task C is the only non-critical task:
it has a duration of 2 but sits on a branch with 2 units of slack (total float),
so it can slip up to 2 time units without delaying the project. The per-task table
shows, for example, that C has earliest start 3, earliest finish 5, latest start
5, latest finish 7 — confirming its float of 2.
FAQ
What is the critical path?
The critical path is the longest chain of dependent tasks through your project. Its length equals the shortest possible project duration, and every task on it has zero float — delaying any of them delays the entire project. There can be more than one critical path; this tool marks every zero-float task as critical and shows one representative path.
What is the difference between total float and free float?
Total float (or slack) is how long a task can be delayed without pushing out the project finish. Free float is how long it can be delayed without delaying its own successors' earliest start. Free float is always less than or equal to total float, and both are zero for critical tasks.
How do earliest and latest start/finish get calculated?
A forward pass sets each task's earliest start to the maximum earliest finish of its predecessors (0 if it has none), and earliest finish = earliest start + duration. A backward pass then sets each task's latest finish to the minimum latest start of its successors (the project duration if it has none), and latest start = latest finish − duration. Total float is latest start − earliest start.
Can I use PERT three-point estimates?
Yes. Write a duration as optimistic/most-likely/pessimistic, e.g. 2/4/9. The
tool uses the PERT expected time (o + 4·m + p) / 6 as the task duration. You can
mix plain numbers and three-point estimates in the same task list.
What happens if my dependencies contain a loop?
A project schedule must be acyclic, so if the tasks reference each other in a cycle
(for example A depends on C, C depends on B, B depends on A) the tool
reports an error listing the tasks involved instead of producing a schedule. It also
errors if a task lists a predecessor that isn't defined.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool critical-path-calculator "A, 3
B, 4, A
C, 2, A
D, 5, B, C
E, 1, D"New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/critical-path-calculator/?tasks=A%2C%203%0AB%2C%204%2C%20A%0AC%2C%202%2C%20A%0AD%2C%205%2C%20B%2C%20C%0AE%2C%201%2C%20D&format=reportMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.