Critical Path (CPM) Calculator
Use this free Critical Path Method calculator to identify the longest sequence of dependent tasks, estimate the shortest possible project duration, and see how much scheduling flexibility each task has.
Critical Path Calculator
Enter each task's ID, name, duration in days, and immediate predecessor task IDs. Separate multiple predecessors with commas (for example, B,C). Leave predecessors blank when a task can start immediately. The example includes parallel work.
How the Critical Path Is Determined
The critical path is the longest connected sequence of dependent activities that determines a project's minimum duration. Different branches can run at the same time. CPM calculates early and late task start and finish times, then identifies tasks with zero total float.
Example with parallel tasks
Task A takes 5 days. After A, Task B takes 6 days while Task C takes 4 days in parallel. Task D takes 7 days and must wait for both B and C. The critical path is A → B → D, lasting 18 days; Task C has 2 days of total float.
What about eight tasks taking five days each?
If all eight tasks must happen one after another, the path takes 8 × 5 = 40 days. If some tasks overlap, the project could finish sooner. Simply multiplying a task duration by the number of tasks is not a full CPM calculation.
What this estimate includes
This calculator assumes finish-to-start task dependencies with zero lag and a common unit of days. It does not account for weekends, holidays, limited staffing, resource leveling, or fixed-date constraints. Tasks and dependencies must be realistic for the estimate to be useful.