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How Critical Path is Calculated

Open Workbench calculates a project's critical path using a two step process. The following rules govern how this two-step process is conducted:

• Tasks that are part of the longest duration chain are on the critical path.
• Fixed duration tasks are always on the critical path
• Project finish date is the sole reference date used to calculate both the early and late schedules.
• Float can be zero or greater than zero; it cannot be negative.
• Task status has no bearing on dependency violations or the critical path calculation.
• A task that is not on the dependency network cannot have an early schedule or late schedule; hence, it cannot be on the critical path.
• Resource constraints do not affect the critical path calculation.

To arrive at the critical path, Open Workbench performs two passes through the dependency network.

The First Pass

The first pass works forward through the network to determine the early start and early end dates for each task in the network, and calculates the longest duration path through the network. The project's reference end date is the project's defined finish date. If you did not define this date, the end date is the early end date of the last task in the network or, if there is more than one branch, the latest of the early end dates of the last task in each branch.

To calculate the early start date for the task's successor(s), Open Workbench starts with the first task in the network and adds the task's duration to the start date. Adjustments are made for gaps or overlaps by adding or subtracting from the duration. The early end date is calculated by adding the task's duration to the early start date. Open Workbench repeats this process for each task in the network.

Note: The successor of a Start-Start dependency has the same early start date as the predecessor. The successor of a Finish-Finish dependency has the same early end date as the predecessor.

The Second Pass

The second pass works backward through the network starting from the project finish date to determine each task's late start and late end date. The last task of each branch of the network has a late end date equal to the project finish date. To calculate the late end date for a task's predecessor(s), Open Workbench subtracts the task's duration from the project finish date. Adjustments are made for gaps or overlaps by adding or subtracting from the duration. The late start date is calculated by subtracting the task's duration from the late end date. Open Workbench repeats this process for each task in the network.

Note: The predecessor of a Start-Start dependency has the same late start date as the successor. The predecessor of a Finish-Finish dependency has the same late end date as the successor.

Calculate Float

Open Workbench calculates the float for each task by subtracting the early start date from the late start date. Float is the number of days that a task's initiation or completion can be delayed without adversely affecting the project finish date. Float is calculated using the following formula: Late Start - Early Start. Tasks with a float of zero (0) appear on the critical path.

More information:

Manually Schedule Projects

About Dependency Relationships