The Differences Between a WBS & Work Schedules

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A work breakdown structure (WBS) is like an organizational chart for a project. An end product or outcome is at the top of the chart with products, tasks or outcomes required to complete it at lower levels. WBSs can be several levels deep and provide the structure for a project. Detailed project documents support the WBS. One of those details is a project work schedule. A work schedule includes the start and complete dates for the tasks, activities or products identified in the WBS. A WBS needs the supporting work schedule to plan a project.


A WBS is designed to completely describe the products, outcomes and tasks required to be performed. It does this in a way that links the end product or outcome with supporting products and tasks in a hierarchy similar to a bill of material or organizational chart. A WBS does not provide other details like a work schedule. Work schedules support the project planning by providing start and complete dates for products and tasks identified in the WBS. Work schedules can also be used for ongoing, non-project work such as manufacturing fabrication and assembly.

Product vs. Process

Originally WBSs were product-oriented, identifying not only parts and assemblies but systems and technology required for a project. WBSs are also used to identify process-oriented projects, including implementing large software systems and engineering design projects. Work schedules also can be applied to products or processes. For example, in manufacturing environments material requirements planning (MRP) software provides material schedules that result in purchasing and manufacturing work. Shop floor scheduling software provides work schedules that consider standard labor and equipment hours required to perform a production run. Project management software develops work schedules with inputs for labor, resources and links between project tasks.

Cost Management

WBSs provide a mechanism to provide estimated costs for the different elements of the WBS and to sum up, or roll up, the costs. WBSs can also be used to collect actual costs for comparison to the original estimates. Work schedules can provide input for timing of costs or time-phasing of costs. Both estimated and actual project costs can be viewed over time using project management software. Time-phased estimated or actual costs can also be provided by cost accounting software.


WBSs can be implemented manually or with technology. Work schedules involve more detail and change more often requiring software systems for project management or manufacturing planning and control.