Project Scheduling

Good Project Scheduling Practice

Project managers typically learn to use project scheduling software by the seat of their pants (or skirt), in other words, self-learning. They don’t have the time to attend a course so they battle through on their own or ask for help from a colleague whose seat of their pants is already worn through. Therefore, many people preparing schedules do not understand basic scheduling concepts and utilize incorrect techniques.

To prepare a correct schedule the Work Breakdown Structure and Critical Path Method (CPM) must be understood.

Schedule network analysis uses the logic relationship between project tasks and the duration of each task to determine how long the project will take. If resources, (with their availability), and the effort (hours of work) are identified for the project tasks, the network analysis will use this additional information to determine how long the project will take.

CPM consists of a forward and backward pass. The forward pass determines the earliest times that each task can start and finish, and the overall project duration. The backward pass determines the latest start and finish for each task. The critical path are the tasks whose early and late dates are equal (they have no float) which is also the sequence of tasks that adds up to the overall longest duration.

Total float is the amount of time a task can be delayed without delaying the overall project completion date. Free float is the amount of time a task can be delayed without delaying the early start of any other task in the schedule.


Here are some suggestions on good practice when preparing a project schedule:

  • Appropriate logic. A common logic mistake is using a start-to-start relationship with a lag, when a finish-to-finish with a lag is more appropriate. If Task B can’t finish until Task A is complete, then finish-to-finish is the correct relationship.
  • Using a start-to-start means that Task B can start once A starts and the lag period is reached, and that Task B can go on to completion. However, it assumes Task A will be completed as planned – which may not be valid.

  • Contingency. Most people include a contingency when preparing the project budget. They recognize that “things happen,” and extra funds are needed to handle unknowns. It is just as important for schedulers to include a schedule contingency. Add it just before the project complete milestone.
     
  • Insert project start and end milestones. The first “task” in your schedule should be a project start milestone, and the last task should be a project end milestone. This provides an easy way to link project tasks to a predecessor or successor when there are no other obvious ties to other project tasks.
     
  • Use fixed duration task type. Scheduling software typically allows you to select which task type – fixed duration, fixed work and fixed units – you want to use for schedule calculations. The fixed duration task type should be used in almost all cases. Fixed work can be used if you resource load a schedule, and provided you want the duration to change based on work and availability.
     
  • Include the header, footer and legend. It’s frustrating to view a schedule that doesn’t list the project name and/or the status date. Use header, footer and legend and include the project title, the date of the update, page number, total pages, the name of the person who did the update, the revision number, file location and file name.

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