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Understand when and how to use a Gantt chart on a project.  Learn how to create a Gantt chart.

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Quick reference

Gantt Chart 

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.

Instructions

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.

  1. List the project phases (Gantt Charts are often created one phase at a time).
  2. Within each phase list the summary level tasks and their associated detail tasks.  The summary tasks are often associated with a major project deliverable.
  3. For each task set the estimated task duration (use the units of the Gantt Chart timeline).
  4. Link the tasks that must occur in the project in a sequential manner.
  5. Either:         
    • 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.
  6. Record the placement of tasks, the start date, end date, and duration on the timeline.
  7. Insert any risk mitigation changes, such as adding buffers between high risk tasks.
  8. 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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  • 00:05 Hi, I'm Ray Sheen.
  • 00:06 Let's talk about schedule planning again, and this time we'll use the Gantt chart or
  • 00:10 as its proper name, the bar chart.
  • 00:14 The Gantt chart is the most commonly used chart for
  • 00:17 scheduling purposes in project management.
  • 00:19 It can be used for project planning, but it is best suited for
  • 00:22 tracking progress on the project.
  • 00:24 It's actually rather clunky for planning.
  • 00:26 The project management body of knowledge, the PMBOK Guide, defines a Gantt
  • 00:31 chart as a bar chart of schedule information where activities are listed on
  • 00:36 the vertical axis, dates are shown on the horizontal axis, and activity durations
  • 00:41 are shown as horizontal bars placed according to start and finish dates.
  • 00:45 Now that's quite a mouthful, but it just means that we show activities on
  • 00:49 the calendar based upon when they're scheduled to occur.
  • 00:53 The Gantt chart can be used either summary level information or detailed tasks.
  • 00:59 I often use the summary level information in my Gantt chart
  • 01:02 at the beginning of a project and detailed tasks are added later one phase at a time.
  • 01:08 The Gantt chart is ideally suited for tracking project because it focuses on
  • 01:12 which activities should be started and finished on any given day.
  • 01:16 The best use of the Gantt chart is daily or
  • 01:18 weekly tracking of progress provided the estimates are accurate.
  • 01:23 This is an example of a Gantt chart.
  • 01:25 You can see the summary task which encompass several detail tasks.
  • 01:29 The edges of the summary task are at the earliest start time
  • 01:32 of the earliest detail task that is being summarized and the latest finish time for
  • 01:37 the last detail task within the summary.
  • 01:40 The detail task bar represents the length of time planned for that detailed task.
  • 01:45 The edges of the bar show the task's start and finish date.
  • 01:49 Now let me take you through the steps for creating a Gantt or bar chart.
  • 01:53 First, list all your project phases in order.
  • 01:56 This will be your highest level of summary tasks.
  • 02:00 Next, list the summary level activities and
  • 02:02 any known detail tasks within each phase.
  • 02:05 Note that we haven't yet started to put down any dates,
  • 02:07 just listing all the tasks activities or deliverables that are known at this time.
  • 02:12 Your work breakdown structure is very helpful for doing this.
  • 02:15 Third, estimate a duration for each task.
  • 02:17 Now this estimate cannot be a range.
  • 02:19 It must be a finite value of calendar time.
  • 02:23 Fourth, link any of the tasks that must occur in a sequential manner.
  • 02:27 Link the end of the first task to the beginning of the second task in
  • 02:31 the sequence.
  • 02:31 After a multiple task in the sequence, continue on through that linking process.
  • 02:37 Now we can finally set dates.
  • 02:39 You can either start from the beginning date and go forward in time, or
  • 02:42 you can start from the end date of the last task and go backward in time.
  • 02:46 If starting from the beginning of a project, set the start date for
  • 02:49 all the tasks that can begin immediately on the start date of the project or phase.
  • 02:53 Each of these tasks will end based upon their plan of duration.
  • 02:57 For those that are linked, start them as soon as the predecessor task is completed.
  • 03:01 Continue until you have planned all the tasks.
  • 03:03 The latest end date for the last task is when the project will end.
  • 03:08 If working from the end date back, set the finish date for all tasks that are at
  • 03:13 the end of a sequence creating a final deliverable on the project or phase.
  • 03:18 Set the start date then by subtracting the duration from that finish date.
  • 03:21 This start date is now the end date for all the predecessor tasks.
  • 03:26 Continue with all of the tasks and
  • 03:28 sequences until you've planned all the tasks.
  • 03:31 The earliest start date for the first task is when the project or phase must start.
  • 03:35 This step can get very ugly in a large project if doing it manually,
  • 03:39 which is why I often break things into phases.
  • 03:42 Many project management software applications will do this for
  • 03:45 you automatically, once you provide the links between the tasks and
  • 03:48 the task duration estimates.
  • 03:51 Finally, plot the calculated start and end dates for
  • 03:53 each of these tasks on the calendar.
  • 03:55 Step 7 isn't really a planning step, it's a tracking step.
  • 03:59 Once all activities have been placed on the Gantt chart,
  • 04:02 the project schedule status can be easily be tracked.
  • 04:04 For any date, the Gantt chart will show what task should be finished, what task
  • 04:08 should be underway, and how much progress should have been made on those tasks.
  • 04:13 Some hints and tips with respect to Gantt charts.
  • 04:16 The Gantt chart is the easiest project schedule chart to read and understand,
  • 04:20 which is one of the reasons why it's so popular.
  • 04:23 You can use different colors on the bars to show additional information
  • 04:26 such as a critical path, behind schedule condition, or who's responsible for
  • 04:31 the task.
  • 04:31 But now for the huge weakness of the Gantt chart with respect to doing projects,
  • 04:36 the Gantt chart relies on accurate and precise duration estimates for
  • 04:40 each activity.
  • 04:41 And if the estimates are wrong, the entire Gantt chart will be wrong.
  • 04:44 This leads to problems with team members and
  • 04:46 stakeholders who make plans to do other project or business activities
  • 04:50 based upon the expectation that the Gantt chart schedule was accurate.
  • 04:54 But on almost all projects some task estimates are uncertain.
  • 04:57 That's the nature of project work as compared to process work.
  • 05:01 Process are usually stable and
  • 05:02 well-defined work streams that can be precisely estimated.
  • 05:06 Projects often contain a unique or different tasks that are highly variable.
  • 05:11 So in working with projects that contain many variable tasks or
  • 05:14 activities, I recommend using the network diagram chart or
  • 05:17 Kanban chart, which will be covered in other lessons.
  • 05:20 Final tip is to start with a summary level Gantt chart.
  • 05:23 It often will be accurate because the uncertainties in detailed tasks can cancel
  • 05:28 each other out.
  • 05:30 As a phase starts, I then create the detailed Gantt chart for just that phase.
  • 05:35 Hopefully, some of the uncertainty is now resolved.
  • 05:40 As I said at the beginning of this lesson,
  • 05:42 the Gantt chart is the most commonly used project scheduling tool.
  • 05:45 While often used for planning, we'll see its real power when we discuss this tool
  • 05:50 during our project tracking and control lessons.

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