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The Gantt Chart is a project schedule tool that shows summary and detail tasks represented by horizontal bars on a schedule timeline.
When to use
The Gantt Chart should be used on predictive projects. It is helpful for organizing schedule planning information because of its graphical display. However, its best use is in schedule tracking.
The Gantt Chart is the most commonly used project schedule chart – although it probably shouldn’t be. It is easy to create and to read. However, its major flaw is that it is based upon the assumption that all estimates of task duration are accurate. This assumption is often false, either because of the inherent uncertainty in the work, the vagueness of the requirements, or the unpredictable availability of resources. However, when the estimates are accurate the Gantt chart format provides great schedule perspective for the project. It is easy to see what tasks the project team should be working on each day, and it is easy to see if adequate progress has been made by changing the color of completed tasks. When being used for tracking progress, I always add a “time now” line on the current date of the project to indicate how much progress should have been made.
- List the project phases (Gantt Charts are often created one phase at a time).
- Within each phase list the summary level tasks and their associated detail tasks. The summary tasks are often associated with a major project deliverable.
- For each task set the estimated task duration (use the units of the Gantt Chart timeline).
- Link the tasks that must occur in the project in a sequential manner.
- Starting with the project start date and the first task, go forward in time plotting all the tasks on the timeline based upon their linkages; or
- Starting with the project end date and the last task, go backward in time plotting all the tasks on the timeline based upon their linkages.
- Record the placement of tasks, the start date, end date, and duration on the timeline.
- Insert any risk mitigation changes, such as adding buffers between high risk tasks.
- As the project progresses, change the color of completed task bars to show they are finished.
Hints & tips
- The Gantt Chart is the easiest project schedule chart to read and understand.
- Start with a summary level Gantt Chart and create detailed Gantt Charts for each phase.
- Draw a vertical line on the timeline showing “time now” and move the line along the timeline as the project progresses. It will show what work the project team should be doing and you can easily track whether you are ahead or behind schedule.
- Different color bars can be used to show additional information about a task, such as critical path, behind schedule, or task is complete.
- The Gantt Chart relies on accurate and precise estimates for each activity. Using inaccurate estimates sets false expectations because team members try to meet the estimates, even though they quickly realize that some are wrong; and stakeholders begin to doubt the credibility of the project team when the actual durations are often different from the estimates.
- The Gantt Chart cannot be created with variable estimates. If you have that situation either use a Network Diagram or start with the “most likely” estimate and build in a risk buffer.
- Gantt Chart: “A bar chart of schedule information where activities are listed on the vertical axis, dates are shown on the horizontal axis, and activity durations are shown as horizontal bars placed according to start and finish dates.” PMBOK® Guide
This definition is taken from the Glossary of the Project Management Institute, A Guide to the Project Management Body of Knowledge, (PMBOK® Guide) – Sixth Edition, Project Management Institute, Inc., 2017.
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PMI, PMP and PMBOK are registered marks of the Project Management Institute, Inc.