Critical Path Calculator
Calculate project critical path and identify task dependencies
ES = Early Start, EF = Early Finish, LS = Late Start, LF = Late Finish. Critical tasks (zero slack) are highlighted.
What is Critical Path Calculator?
The Critical Path Calculator is a free project management tool that applies the Critical Path Method (CPM) to find the longest chain of dependent tasks through your project — the sequence that determines the shortest possible completion time. You add each task with its duration and the tasks it depends on (its predecessors), and the tool identifies which tasks are critical, calculates the total project duration, and shows the slack on every non-critical task. For each task it computes the four core CPM figures — Early Start (ES), Early Finish (EF), Late Start (LS) and Late Finish (LF) — and the resulting float, presenting them in a full schedule table. The ordered critical path is highlighted as a chain, and built-in starter templates for software, construction, and event projects let you explore a realistic network in one click. Everything is calculated instantly in your browser, with no signup and no data leaving your machine.
How to use Critical Path Calculator?
Finding your project's critical path takes only a few minutes:
- 1 Start from scratch by adding tasks, or load a starter template — software, construction, or event planning — to see a complete dependency network instantly. Give each task a name, an estimated duration in days, and its dependencies (the task numbers that must finish before it can start). Accurate dependencies are essential for a correct result.
- 2 Let the tool calculate the critical path using the CPM algorithm. It topologically orders the network, then performs a forward and backward pass to find the Early Start, Early Finish, Late Start, and Late Finish for every task and the longest path through the network.
- 3 Review the results: the critical tasks are highlighted, the total project duration is shown in days, the ordered critical path is drawn as a chain, and a schedule table lists ES, EF, LS, LF, and slack for every task — the time each one can slip without delaying the project.
- 4 Focus your management attention on the critical tasks, because they have zero float and directly drive the end date. Keep the model updated as durations and dependencies change throughout the project. If you create a loop by mistake, the tool warns you about the circular dependency.
Why use this tool?
On any project of meaningful size, not all tasks matter equally to the deadline. The critical path reveals exactly which ones do, so managers can concentrate monitoring, resources, and contingency on the tasks that truly control the finish date instead of spreading attention thinly. It also exposes slack on non-critical work, showing where schedules have flexibility and where they do not. This makes trade-offs explicit when something slips: a delay on a task with float may be harmless, while a delay on a critical task demands immediate action. Because the calculator runs locally in your browser, your project structure stays private, and the method scales from small plans to complex dependency networks.
Examples
Design (5 days) → Develop (10 days) → Test (3 days) runs in sequence for an 18-day critical path. Every task is critical because each must finish before the next can start, so all three show zero slack in the schedule table.
A documentation task runs in parallel with a 10-day development task but needs only 4 days. The table shows ES 0, EF 4, LS 6, LF 10 and 6 days of slack, so it can start later without affecting the project end date.
Load the software project template to get seven linked tasks — from Requirements through Deployment — already wired with predecessors, then tweak durations to model your own plan and watch the critical path update live.
Frequently Asked Questions
What exactly is the critical path?
It is the longest sequence of dependent tasks through the project. Its total duration equals the shortest time in which the project can finish, so any delay along it delays the whole project.
What do ES, EF, LS, and LF mean?
Early Start and Early Finish are the soonest a task can begin and end given its predecessors. Late Start and Late Finish are the latest it can begin and end without delaying the project. The gap between them is the slack, and the tool lists all four for every task.
What does slack or float mean?
Slack is the amount of time a task can be delayed without pushing the project end date later. Critical tasks have zero slack, while non-critical tasks have some flexibility shown in the schedule table.
How do I enter dependencies correctly?
For each task, list the numbers of the tasks that must be fully complete before it can begin, separated by commas. Getting dependencies right is essential, because the critical path is determined entirely by how tasks connect. If you accidentally create a loop, the tool flags the circular dependency.
Can a project have more than one critical path?
Yes. When two or more chains share the same longest duration, they are all critical. In that case every task on each of those chains needs close monitoring.
Is my project data stored anywhere?
No. The CPM calculation runs entirely in your browser, so your task list, durations, and dependencies are never uploaded to or saved on a server.
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