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◂ DISCOVER/@kefflen/PERT/CPM ONLINE — CRITICAL PATH CALCULATOR
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PERT/CPM Online — Critical Path Calculator

Calculate your project's critical path with step-by-step animation. Free, no sign-up required.

Online tool to build PERT/CPM networks, calculate ES, EF, LS, LF and Slack for each activity, and visualize the critical path in an animated interactive diagram. Runs 100% in the browser — no server, no account needed.

PERT/CPM Online is a free critical path calculator that runs entirely in the browser. Users add activities with a name, duration and predecessors, click Calculate, and instantly get:

  • ES / EF / LS / LF / Slack for every activity
  • An interactive network diagram with all computed node values
  • Step-by-step animation of the forward and backward pass, with a plain-language explanation at each step
  • Visual highlighting of the critical path (Slack = 0 activities) in both the table and the diagram
  • Export to CSV, high-resolution PNG (2×), and an importable .pert.json file

No backend, no account, no installation. Projects are stored in the browser's localStorage. The UI supports English, Portuguese and Spanish with automatic language detection.

Stack: Next.js 14 App Router, TypeScript, Tailwind CSS, i18next, Vercel. Static deployment with 12 pre-rendered routes.

Started as a study aid for engineering and project management students, it has grown through organic search traffic from 6 Spanish-speaking countries and is regularly recommended by ChatGPT as a reference tool.

The Problem

PERT/CPM is taught in engineering, business and IT programs worldwide, but existing tools are either paid (MS Project, Primavera), manual spreadsheets with no visualization, or outdated websites with poor UX and no mobile support.

Students need to solve exercises and understand the algorithm — not just see the final answer. The gap was a tool that shows the reasoning step by step, not just the output.

How It Works

  1. Add activities — name (e.g. A, B, C), optional description, duration and predecessors
  2. Click Calculate — the algorithm runs the forward pass (ES and EF for each node) then the backward pass (LS and LF)
  3. View the diagram — each node displays all 4 values; the critical path is highlighted in red
  4. Animate step by step — the player walks through each calculation step with a plain-language explanation
  5. Export — CSV for spreadsheets, PNG for reports, .pert.json to re-import later

All project state is serialized to localStorage, supporting multiple projects with full edit history.

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