Critical Path Calculator
Not Every Task on the List Actually Controls the Deadline
On any project with parallel workstreams, some tasks can slip a few days without moving the finish date at all — and others can't slip by even a single day without delaying everything downstream. The chain of tasks with zero slack is the critical path, and it's the only chain that matters when someone asks "can we hit the deadline?" This calculator compares multiple task-duration paths and identifies which one actually drives the project length.
The Formula
Each line you enter represents one path through the project — a chain of dependent tasks. The calculator sums the durations on each path and reports whichever path totals the highest; that total is the minimum possible project duration.
Where This Is Useful
- Identifying schedule risk — tasks on the critical path deserve the closest monitoring, since any delay there delays the whole project.
- Deciding where to add resources — shortening a non-critical path does nothing for the deadline; shortening the critical path does.
- Explaining "why can't we go faster" — a side-by-side path comparison makes it concrete which sequence of tasks is actually the bottleneck.
Worked Example
Three parallel paths through the same project, entered one per line:
| Path | Task durations (days) | Total |
|---|---|---|
| Path 1 | 5, 3, 8, 2 | 18 |
| Path 2 | 4, 6, 7 | 17 |
| Path 3 | 6, 6, 6, 6 | 24 |
Path 3 is the critical path at 24 days — even though Paths 1 and 2 finish sooner, the project as a whole cannot finish before Path 3 does.
How to Use This Calculator
- In the paths box, enter one path per line.
- For each path, list the task durations as comma-separated numbers (for example,
5,3,8,2). - Select Calculate to see the total for every path and which one is the critical path.
Related Calculations
Once you know the critical path length, check overall project length with the Project Timeline Calculator, or lay it out day by day with the Gantt Chart Duration Calculator.