MATH

Project Critical Path Calculator

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Find project duration, early and late task times, and zero-slack tasks in a dependency graph.

Your result

MATH

Enter your values and select calculate.

On this page How it works & practical examples

How to use the Project Critical Path Calculator

Use one duration unit for all tasks. IDs must be unique and dependencies must refer to other listed tasks. The calculator validates cycles, computes a forward pass for earliest times and a backward pass for latest times, and provides a downloadable task table.

The calculation

Earliest start = max(predecessor finishes); late finish = min(successor late starts); slack = late start − early start

Worked example

A takes 3 units, then B takes 2 and C takes 4 in parallel. D takes 1 after both finish. Project duration is 8 units; A, C and D have zero slack.

Assumptions and limits

Assumes finish-to-start dependencies with zero lag and unlimited parallel resources. Resource leveling, working-day calendars, uncertainty and special dependency types are not modeled. Multiple critical paths may exist.

Common questions

Does zero slack always identify one path?

No. Several parallel routes can be critical. The result lists zero-slack tasks rather than inventing a single path.

Can two tasks share a limited team?

This model does not constrain resources. Such a constraint can lengthen the actual project schedule.