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Free Tool · Updated March 2026

Free Critical Path Calculator
Find Your Longest Path

I used the critical path method on every major project I managed in the UAE, including EGA Head Office and The Constellation. Enter your project tasks, durations and dependencies and get instant forward pass, backward pass, Early Start, Early Finish, Late Start, Late Finish dates, total float, free float and critical path identification. No signup, no download.

✓Full CPM engine. Forward and backward pass.
✓Updated March 2026
✓Float, ES, EF, LS, LF all calculated
✓Free. No login needed.

Critical Path Calculator

Enter tasks below, then click Calculate to find your critical path

CPM Engine 2026
Project Tasks
#
Task Name
Duration
Predecessors (comma-separated IDs)
Duration unit = days (or any consistent unit)
0
Project Duration
(days)
0
Total Tasks
0
Critical Path
Tasks
0
Tasks with
Float
Critical Path
TaskDurationESEFLSLFTotal FloatFree FloatCritical?
Network Diagram
How to Use This Calculator
Critical path calculator steps: activities, dependencies, forward and backward pass
How the critical path calculator works.
Quick answer

A critical path calculator is a free tool that finds the longest sequence of dependent activities in a project, which sets the shortest possible finish date. Enter each activity, its duration and its predecessors, and it calculates early and late dates, total float and the critical path.

How to Calculate the Critical Path

Step 1: Add your tasks. Click "+ Add Task" for each activity in your project. Give each task a name and its duration in days, or any consistent unit such as hours or weeks, as long as you stay consistent.

Step 2: Set dependencies. In the Predecessors column, enter the ID numbers shown in the blue badge for any tasks that must finish before this task can start. Use commas to separate multiple predecessors. For example, "1,3" means both Task 1 and Task 3 must finish before this task starts. Leave the field blank for tasks with no predecessors, which are your start tasks.

Step 3: Click Calculate. The calculator performs the forward pass, calculating ES and EF for every task, and the backward pass, calculating LS and LF. Then it identifies all tasks with Total Float of zero as your critical path.

✦
Quick tip: Click "Load Example" to see a pre-built 8-task project with multiple paths. It demonstrates how the calculator handles parallel paths, merging dependencies and float calculation across a realistic schedule network.
CPM Formulas

What are the critical path formulas?

The Critical Path Method uses two passes through the network to calculate all scheduling values. I used these exact formulas on every schedule I built in the UAE, sometimes by hand before software made it easy.

Forward Pass: Early Start
ES = max(EF of all predecessors)
For start tasks with no predecessors, ES equals 0. For all other tasks, ES is the latest Earliest Finish of all its predecessor tasks. This ensures all predecessor work is complete before the task begins.
Forward Pass: Early Finish
EF = ES + Duration
The earliest a task can complete, assuming it starts at its Early Start. The project's total duration equals the maximum EF across all end tasks, meaning tasks with no successors.
Backward Pass: Late Finish
LF = min(LS of all successors)
For end tasks, LF equals the Project Duration. For all other tasks, LF is the earliest Late Start of all its successor tasks. This is the latest this task can finish without delaying anything downstream.
Backward Pass: Late Start
LS = LF − Duration
The latest a task can begin without delaying the project. When LS equals ES, the task is on the critical path. It has no scheduling flexibility.
Total Float
TF = LS − ES = LF − EF
The maximum amount of time a task can be delayed without delaying the project end date. Tasks on the critical path have TF of zero. Using total float of one task reduces the float of all tasks that share the same path.
Free Float
FF = min(ES of successors) → EF
The amount of time a task can be delayed without delaying any of its immediate successors. Free float is always less than or equal to total float. Unlike total float, using free float does not affect other tasks on the path.

How do you identify the critical path?

A task is on the critical path when Total Float equals zero. The critical path is the continuous chain of zero-float tasks from the project's first task to the last. It represents the longest path through the network and determines the minimum project duration.

There can be multiple critical paths if two or more paths through the network are equally long. In that case, all tasks on all equally long paths have zero float and are critical.

✦
Near-critical paths matter too. Tasks with very low total float, for example 1 to 2 days on a 3-month project, are near-critical. A small delay or risk event could push them onto the critical path. I always monitored near-critical paths as closely as the critical path itself on my construction projects.
FAQ

Worked example: a 37-day project

ActivityDuration (days)PredecessorEarly start to finishTotal float
A10NoneDays 1 to 100
B12ADays 11 to 220
C8ADays 11 to 184
D15B, CDays 23 to 370

Critical path: A, B, D = 37 days. Activity C can slip by up to 4 days without delaying the project.

Critical Path: 4 Common Questions

The Critical Path Method, or CPM, is a project scheduling technique that identifies the longest sequence of dependent tasks. This sequence is the critical path and it determines the minimum project duration. Any delay to a task on the critical path directly delays the project end date. Tasks not on the critical path have float, which is the amount of time they can slip without affecting the project end date. CPM was developed by DuPont in the late 1950s and remains a core technique in PMP, PRINCE2 and most PM methodologies. I taught this to every PMP student I have trained.
Float, also called slack, is the amount of time a task can be delayed without delaying the overall project completion date. Total Float is the maximum delay a task can absorb without affecting the project end. Free Float is how much a task can slip without delaying any of its immediate successors. Tasks on the critical path have zero total float. Any delay there directly extends the project. Understanding float helps PMs make resource allocation decisions and identify scheduling flexibility during execution.
ES, or Early Start, is the earliest a task can begin. EF, or Early Finish, equals ES plus Duration, the earliest it can complete. LS, or Late Start, is the latest a task can start without delaying the project. LF, or Late Finish, equals LS plus Duration. Total Float equals LS minus ES. These four values are calculated through the forward pass for ES and EF, and the backward pass for LS and LF, of the CPM algorithm. On the PMP exam, these values appear in node diagrams where each task box shows all four corner values.
The critical path is identified by calculating Total Float for every task. Any task with Total Float of zero is on the critical path. The critical path is the continuous chain of zero-float tasks from the project start to the project finish. It is the longest path through the network. If two or more paths are equally long, all of them are critical paths. In the calculator above, critical path tasks are highlighted in violet with a "Critical" badge in the results table.
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