CPM/PERT and Gantt Planner
The critical path method (CPM) schedules a project from its tasks, their durations and the order they must follow. A forward pass gives each task its earliest start and finish, a backward pass gives its latest start and finish, and the difference is its slack. Tasks with zero slack form the critical path: delay any of them and the whole project finishes late. PERT adds uncertainty by asking for 3 duration estimates per task.
The tool opens on cpm-task-data.csv, the 8 tasks of a conference plan, and loads gantt-data.csv to check the published Gantt chart against the schedule it computes. Switch between most likely durations and PERT expected times, set a deadline to see the chance of meeting it, or open Edit tasks to change the plan or build your own.
How it works
Predecessors are given by task name. In the sample file, Staff_Briefing waits for 4 tasks, listed together inside quotes.
Here a, m and b are the optimistic, most likely and pessimistic durations. On the sample file the critical path runs Venue_Booking, Catering_Arrangement, AV_and_Equipment_Setup, Staff_Briefing, Final_Rehearsal, for 16 days on most likely durations and 16.0 days on te.
The passes count days from 0. The Gantt file counts from day 1, so its Start_Day is ES + 1 and its End_Day is EF: Catering_Arrangement has ES 5 and EF 9, and the file shows it on days 6 to 9. The chance of finishing by a deadline T uses the normal approximation z = (T − sum of te) / √(sum of variances) along the critical path. With tied critical paths the tool uses the one with the larger variance.
Frequently Asked Questions
What is the critical path?
The critical path is the longest chain of dependent tasks through a project. Its length is the shortest time the project can take, and every task on it has zero slack, so any delay to one of them delays the finish.
How do you calculate PERT expected time?
PERT expected time is (a + 4m + b) / 6, where a is the optimistic, m the most likely and b the pessimistic duration. Its variance is ((b − a) / 6) squared. Adding the variances along the critical path gives the variance of the project's duration.
What is slack or float?
Slack, also called float, is how long a task can slip before it delays the project. It equals the latest start minus the earliest start. Tasks on the critical path have zero slack.
How does a Gantt chart relate to CPM?
A Gantt chart draws each task as a bar from its start to its finish on a timeline. CPM supplies those start and finish days. This tool draws the bars from the CPM schedule, colours the critical tasks and shows slack as a line after each bar.
Is the CPM/PERT planner free?
Yes. It is free, runs in your browser and keeps your plan on this device. Export the schedule as CSV, PNG or PDF.