Critical Path Analysis Calculator
Enter your project activities below. Use a unique Activity ID (like A, B, Design, QA), a duration, and predecessor IDs separated by commas.
Tip: IDs cannot contain spaces. Example predecessor list: A, C
What is critical path analysis?
Critical Path Analysis (CPA), often called the Critical Path Method (CPM), is a planning technique used to find the longest chain of dependent tasks in a project. That longest chain is the critical path, and it determines the earliest possible completion date.
If any activity on the critical path is delayed, your whole project is delayed by the same amount (unless you recover time later). That is why critical path analysis is essential for project managers, operations teams, construction planners, and product teams.
How this calculator works
1) Forward pass
The calculator computes each activity's earliest start (ES) and earliest finish (EF) by moving from the start of the network to the end. This tells you the soonest each task can happen based on dependencies.
2) Backward pass
Then it computes latest finish (LF) and latest start (LS) by moving backward from project completion. This tells you how late each activity can occur without delaying the project.
3) Slack and critical activities
Slack (or float) is calculated as LS − ES. Activities with zero slack are critical. The calculator highlights those rows and lists critical path sequences.
How to enter data correctly
- Activity ID: unique text label (A, B, Task1, BuildAPI).
- Duration: positive number (days, weeks, hours—just stay consistent).
- Predecessors: IDs that must finish before this task starts.
- Leave predecessors blank if an activity can begin at project start.
- Avoid circular dependencies (for example, A depends on B while B depends on A).
Interpreting the output
After calculation, you'll see the total project duration and a detailed table:
- ES/EF: earliest schedule.
- LS/LF: latest schedule without delaying the project.
- Slack: scheduling flexibility.
- Critical: Yes/No marker for zero-slack activities.
Use this information to focus attention where it matters most: critical tasks, resource bottlenecks, and schedule risks.
Best practices for real projects
Keep activity definitions clear
Each activity should represent a meaningful chunk of work with one owner and one completion condition.
Use realistic durations
Overly optimistic estimates make critical paths look shorter than reality and increase late delivery risk.
Recalculate frequently
As progress changes, rerun the analysis. The critical path can shift during execution.
Track near-critical tasks
Tasks with very low slack can become critical quickly if anything slips.
Quick example
Try the built-in example data to see how the model behaves. You’ll notice one chain of activities controls total duration, while others have slack. That slack can be used for resource leveling or risk buffering.